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Shallow water seagrass fish communities of Intermittently Closed and Open Lakes and Lagoons (ICOLLs) of south-eastern Australia Martine V. Jones University of Wollongong
Jones, Martine V., Shallow water seagrass fish communities of Intermittently Closed and Open Lakes and Lagoons (ICOLLs) of south-eastern Australia, Doctor of Philosophy thesis, Faculty of Science, University of Wollongong, 2003. http://ro.uow.edu.au/theses/1869
This paper is posted at Research Online.
Shallow water seagrass fish communities of
Intermittently Closed and Open Lakes and Lagoons
(ICOLLs) of south-eastern Australia.
By Martine V. Jones
A thesis submitted in partial fulfilment of the requirements for the award of the degree of
DOCTOR OF PHILOSOPHY
ENVIRONMENTAL SCIENCE FACULTY OF SCIENCE THE UNIVERSITY OF WOLLONGONG
2003 u
DECLARATION OF ORIGINALITY
I, Martine V. Jones, declare that this thesis, submitted in fulfilment of the requirements for the award of Doctor of Philosophy, Environmental Science, Faculty of Science, University of
Wollongong, is wholly my own work unless otherwise references or acknowledged. This thesis has not been submitted for qualifications at any other academic institution.
Martine V. Jo HI
Acknowledgements
My deepest and sincere gratitude firstly goes to Professor Ron West for giving me a wonderful opportunity in my career. I will always be grateful for being able to do fish research, and to delve into marine conservation issues. The staff of the Environmental
Science Unit also deserves thanks, especially Sandra Quin, who is amazing in her seemingly unlimited capacity to help people. Also thanks goes to Dr Tony Miskievicz for discussions on fish ecology and great advice; Alex Meehan for his patient help in teaching me to use technology for doing maps, Kerryn Stephens for conversations on estuary management, and
Tim Haeusler for much appreciated help on the Lake Illawarra map.
I was also lucky enough to have fantastic people to come sampling with me and enjoy the splendour of the beautiful south coast of NSW. Weeks of sampling were always fun, even in the cold waters of winter, particularly due to the company of Carla, Terry, Cameron and
Vince.
To the group of friends in my life that helped me get through this and have always had encouragement and kept me sane - thank-you! Most notably, a special thanks goes to Carla,
Luke, Melinda, Charlotte, Kerryn, Alexandra, and Dom. And a special thanks goes to Rob, who met me near the end of all this, but whose patience and support proved invaluable. Also, my sincere gratitude to my parents, Jacquelene and Gareth, my sister Amanda and husband
Justin, and my grandparents, Una and Roy, who have always gave encouragement to my endeavours.
And last but not at all least, I will be forever in debt to the little fishes whose lives were sacrificed in the name of science.
This research was fimdedb y Fisheries Research and Development Corporation (FRDC). IV
ABSTRACT
The structure and dynamics of fish communities associated with shallow water seagrass
habitats were investigated in estuaries along the south-eastem coast of Australia. The
majority of estuarine systems in this region of southeast Australia are intermittently closed
and open lakes and lagoons (ICOLLs). The fish communities within these coastal lakes have
not been previously studied in detail. The sampling method employed in this study was
aimed at the capture of new recmits, mainly small juveniles of marine and estuarine fish
species using the seagrass beds as a nursery habitat, as well as species that were permanent
residents of the seagrass meadows. Research was conducted over a three-year period in eight
estuaries spanning approximately 500km of southem New South Wales (NSW). These
estuaries are Lake Illawarra, St Georges Basin, Lake Conjola, Burrill Lake, Durras Lake,
Coila Lake, Wallaga Lake and Merimbula Lake. Within seven of these estuaries, three
locations representative of the entrance, central and upper locations were sampled quarterly
for three years. Fish sampling was undertaken using a seine net (6mm stretch mesh, 25m
long), primarily in Zostera capricomi seagrass beds. Environmental data was also recorded
during each sampling event, and included salinity, conductivity, temperature, pH and turbidity.
Overall, 101 fish species were found within the region. Within individual estuaries species diversity ranged from 41 to 61 species. The most specious families were the Gobiidae,
Syngnathidae and Monacanthidae. The catch was dominated by large abundances of a few
species, particularly from the Ambassidae, Atherinidae and Gobiidae families. There were
significant spatial and temporal differences in the species diversity of seagrass fish fauna for
each individual estuary. With the exception with Merimbula Lake, spatial and temporal
differences in tiie abundance of fish were also evident. However, there was little consistency to these pattems, either within estuaries or between them. The location factor had little influence on fish diversity and abundance pattems, and there were no decline in species diversity and abundance with increasing distance from the estuary mouth. The largest percentage of variation was due to either lower species diversity or abundance found during the winter months, or large single catches of schooling fish species.
Fish community dynamics were investigated by multivariate analyses. The results indicated that the fish species compositions within each estuary were highly similar on a spatial scale.
There was little compositional change in the fish assemblages with increasing distance from the estuary mouth. Yearly changes in fish community composition were more noticeable than seasonal changes. It was found that the south coast fish fauna was composed of a "core" group of species that were caught consistently throughout time and were found at all locations. There were no 'restricted' species that had sfrong or distinct location-associations within these estuaries. Rather, some species may have had preferences for certain regions but were not restricted to them.
Commercial fish species diversity and abundance pattems were investigated for six of the estuaries, and the recmitment dynamics of five major species were also examined for seven of the estuaries. The major findings were that there was a substantial increase in the strength of recruitment in 1998, and this was evident across all of the selected species and across all estuaries. This indicated that for these commercially important species, processes responsible for widespread and substantial increase in recruitment must be large-scale, and not restrictive processes confined to an individual species life-history characteristics or to a particular local area. Rainfall data from the south coast of NSW, and data relating to El Nino phenomena were discussed as the probable tiigger for the high recmitinent that occurred in the spring/summer of 1998. Overall, there were no consistent sites of recmitinent in these VI
ICOLLs, and pattems of settlement for all species at the three locations within each estuary were not consistent through time. However, there were small regional differences in the timing and magnitude of recmitment in the seven estuaries along a latitudinal scale.
The results from the large-scale sampling program indicated that local processes within individual ICOLLs may be a much more important factor in the stmcturing of these fish communities than differences in geomorphology or biogeography for these ICOLLs. To investigate these local processes in detail, a sampling program was undertaken in two estuaries. Lake Illawarra and Durras Lake. These two estuaries were chosen, as they are very different systems in terms of shape and size, entrance conditions and degree of catchment and lake usage. Sampling of the shallow water seagrass fish communities was conducted at thirty-two sites within each estuary every six weeks for one year. The high degree of similarity in the shallow water fish community around each estuary that was found in the larger sampling program was still evident at a finer scale of sampling, and there were still inconsistent pattems of settlement through time within each estuary. This intensive sampling program provided a clearer understanding of the effects of individual lake morphology and hydrology on fish community pattems.
Consideration of the information and conclusions from the two sampling programs have led to a number of hypotheses. It is proposed that lake morphology, individual hydrological characteristics and the local climatic regime are important determinants in the stracturing of
ICOLL fish assemblages in southeast Ausfralia. The pattems in fish diversity and abundance, and in community dynamics were contrary to traditional concepts of estuarine fish pattems, which have been largely developed from research carried out in large riverine and permanently open estuaries, or in intermittently open estuaries where there are distinct seasonal rainfall pattems that influence the salinity gradients within the estuary. It would Vll appear that the small size of ICOLLs in southem NSW, lack of seasonal rainfall pattems, the dominance of wind-induced fransport rather than tidal-induced water transport, and the relatively stable salinity around the perimeter of the ICOLLs allows the widespread distribution of marine spawning species within these systems.
This research has direct implications for the sustainable management and conservation of
ICOLL environments and their fish communities. These coastal lakes were found to be important fish habitats, particularly in terms of their role as recmitment and nursery areas for a wide range of marine and estuarine species. However there were few, if any, consistent pattems in species recmitment, diversity and abundance, either between locations within estuaries, between estuaries within the region, or between seasons and years. Local hydrology, morphology and climate affecting individual ICOLLs are the most important factors stmcturing fish communities. Currently these ICOLLs are managed using a generic
approach, based on the assumption that different ICOLLs have similar ecological characteristics. Based on the results from this research, the most suitable approach for management purposes is to consider each estuary as a unique situation requiring a detailed
and localised approach. VIU
Publications related to this research
West, R.J., and Jones, M.V. (2001). Shallow water fish communities of New South Wales south coast estuaries. FRDC Project 97/204. University of Wollongong. Ocean and Coastal
Research Cenfre. Report Series Nos.2001/11. 135pp IX
TABLE OF CONTENTS
Titie Declaration of Originality ii Acknowledgments iii: Abstract iv Publication related to this research viii Table of Contents ix: List of Figures xv List of Tables xxviii
Chapter One Introduction 1.1 General infroducti on ,,, 1 1.2 Statement of the problem 3 1.3 Present gaps in knowledge 4 1.4 Thesis objectives 6 1.5 Thesis stmcture 7 1.6 Characteristics of study region 9 1.6.1 Climatic conditions 9 1.6.2 Coastal environments 11 1.7 Study sites 11 Lake Illawarra 11 St Georges Basin 13 Lake Conjola 14 Burrill Lake 15 Coila Lake 17 Wa llaga Lake 18 Merimbula Lake 19 Chapter Two Literature Review 2.1 General Infroduction 20 2.2 The estuarine environment of NSW 21 2.3 Factors influencing fish community stmcture 24 2.3.1 Biological factors 24 2.3.2 Physical and chemical factors 26 2.4 Life history categorisation of fishes in estuaries 30 2.5 Intermittently Closed and Open Lakes and Lagoons (ICOLLs) 31 2.6 Recmitment of marine fish species 34 2.7 Recmitment of temperate fish to estuarine seagrass meadows 36 2.8 Sampling of estuarine fish communities in shallow water seagrass habitats 38 2.9 Management and conservation of estuaries 40 2.9.1 Conservation status of estuarine species and issues of rarity 41 2.9.2 Marine protected areas 42 2.9.3 Monitoring of estuarine health 44
Chapter Three Large-scale spatial and temporal variability in species diversity and abundance of fish communities from south-eastern Australian estuaries 3.1 Infroduction 46 3.2 Pilot stiidy 49 3.2.1 Inti-oduction 49 3.2.2 Method 50 3.2.3 Results 51 3.3 Method 52 3.3.1 Site location 52 3.3.2 Water quality 54 3.3.3 Fish sampling 54 3.3.4 Data analysis 55 3.4 Results 64 3.4.1 Environmental Data 64 XI
3.4.2 General overview offish communities 69 3.4.3 Overall pattems in mean species diversity and abundance 74 3.4.3.1 The influence of environmental variables on diversity and abundance pattems 76 3.4.4 Spatial and temporal variabihty in fish species diversity and abundance witiiin ICOLLs 78 3.4.4.1 Lake Illawarra 79 3.4.4.2 St Georges Basin 84 3.4.4.3 Lake Conjola 87 3.4.4.4 Burrill Lake 90 3.4.4.5 Coila Lake 93 3.4.4.6 Wallaga Lake 96 3.4.4.7 Merimbula Lake 99 3.5 Discussion 102 3.5.1 ICOLL fish species diversity mid abundance.... 102 3.5.2 Within-estuary variability in fish species diversity and abundance 104 3.5.3 Variability in pattems of species diversity and abundance 108
Chapter Four Community changes in the fish assemblages of six intermittently closed and open estuaries of SE Australia 4.1 Infroduction 112 4.2 Methods 115 4.2.1 Field sampling 115 4.2.2 Data analysis 116 4.3 Results 117 4.3.1 Pattems in fish communities within and between estuaries 117 4.3.2 Species-site associations 122 4.3.2.1 General overview 122 4.3.2.2 Core group of species 129 4.3.2.3 Pattems of species-association within individual ICOLLs 137 4.3.3 Similarity of fish community stmcture in a regional scale 140 4.3.4 Evaluation of rare species 144 Xll
4.4 Discussion 149 4.4.1 Fish assemblages of SE Ausfa-alian ICOLLs 150 4.4.2 Seasonal and yearly variability in fish assemblages 152 4.4.3 Influence of ICOLL morphology and hydrology on fish community stmcture... 154 4.4.4 Evaluation of conservation status 157 4.4.5 Geographic pattems 160 4.4.6 Effects of opening and closing 162 4.4.7 Conservation and management impHcations 164
Chapter Five Spatio-temporal variation in the recruitment of major commercial fish species to SE Australian ICOLLs 5.1 Introduction 168 5.2 Methods 172 5.2.1 Field sampling 172 5.2.2 Data analysis 172 5.3 Results 173 5.3.1 General summary 173 5.3.2. Acanthopagrus australis (Gunther 1859) 176 5.3.2.1 Discussion of Results 178 5.3.3 Girella tricuspidata (Quoy and Gaimard 184) 189 5.3.3.1 Discussion of Results 190 5.3.4 Meuschenia trachylepis (Gunther 1870) 198 5.3.4.1 Discussion of Results 199 5.3.5 Monacanthus chinensis (Osbeck 1765) 207 5.3.5.1 Discussion of Results 207 5.3.6 Gerres subfasciatus (Gunther 1859) 213 5.3.6.1 Discussion of Results 213 5.4 Conclusion 220 5.4.1 Major findings 220 5.4.2 Summary of spatio-temporal pattems in recmitment events , 220 5.4.3 Temporal pattems in recmitment 222 5.4.4 Spatial pattems of settlement within estuaries 227 XIU
5.4.5 Regional differences in recmitment 229 5.4.6 Recommendations 232
Chapter Six Small-scale spatial differences in the shallow water fish communities of two intermittently closed and open lakes 6.1 Introduction 234 6.2 Methods 236 6.2.1 Study sites 236 6.2.2 Site selection 236 6.2.3 Fish sampling 237 6.2.4 Data analysis 237 6.3 Results 241 6.3.1 Entrance conditions 241 6.3.2 Salinity and temperature 241 6.3.3 Fish communities 244 6.3.3.1 Lake Illawarra 244 6.3.3.2 Durras Lake 254 6.3.4 Spatial and temporal pattems of commercial fish species 264 6.3.4.1 Acanthopagrus australis 266 6.3.4.2 Girella tricuspidata 271 6.3.4.3 Gerres subfasiatus 273 6.3.4.4 Rhabdosargus sarba 273 6.4 Discussion 277 6.4.1 Stmcturing offish communities within estuaries 277 6.4.2 Influence of physical factors on small-scale spatial and temporal pattems 279 6.4.3 Comparisons with large-scale sampling program 282 6.4.4 Conservation and management implications 286
Chapter Seven Conclusions and Recommendations 7.1 Introduction 291 XIV
7.2 Large-scale and small-scale spatial and temporal variability in diversity 291 and abundance of fish in seagrass beds 7.3 Seagrass fish communities in SE AusfraHa, and pattems in the species assemblages within and between estuaries 292 7.4 Recmitment pattems of commercially and recreationally exploited fish species within ICOLLs along the south-east Ausfralian coastline 293 7.5 Major conclusions 294 7.6 Management and conservation implications 295
References 3 06 Appendix 1 340 XV
LIST OF FIGURES
Figure 1.1: Map of study region in southeast New South Wales, showing the eight estuaries included in the research program. 10
Figure 3.1: Relationship between the number of replicates and minimum detectable effect size (A), statistical power (B) and benefit cost-ration (C). Figure 3,1(A) shows data for numbers of individual fish and number offish species whereas Figure 3,1(B) and 3,1(C) show data for numbers of individuals only 52
Figure 3.2: Entrance, Central and Upper sampling locations in Lake Illawarra, NSW. See Figure 1.1 for map of region 57
Figure 3.3: Entrance, Central and Upper sampling locations in St Georges Basin, NSW. See Figure 1.1 for map of region 58
Figure 3.4: Entrance, Central and Upper sampling locations in Lake Conjola, NSW. See Figure 1.1 for map of region 59
Figure 3.5: Entrance, Central and Upper sampling locations in Burrill Lake, NSW, See Figure 1.1 for map of region 60
Figure 3.6: Entrance, Central and Upper sampling locations in Coila Lake, NSW. See Figure 1.1 for map of region 61
Figure 3.7: Entrance, Central and Upper sampling locations in Wallaga Lake, NSW. See Figure 1.1 for map of region 62
Figure 3.8: Entrance, Central and Upper sampling locations in Merimbula Lake, NSW. See Figure 1.1 for map of region 63 XVI
Figure 3.9: Temperature (°C) values taken at each sampling event over the three year period at the entrance, central and upper locations within each of the seven estuaries. Note Merimbula Lake samples for two years only 65
Figure 3.10: Salinity values (parts per thousand) at the entrance, central and upper location within each estuary over the three year sampling period. Note Merimbula Lake sampled for two years only. 66
Figure 3.11: pH values at the entrance, central and upper location within each estuary over the three year period. (Merimbula Lakesampled for two years only). 67
Figure 3.12: Turbidity values (NTU) at the entrance, central and upper location within the seven estuaries over the three year period. Note Merimbula Lake sampled for two years only. 68
Figure 3.13: Mean number offish species caught at the entrance, central and upper locations within each estuary. Lines denote standard error. 75
Figure 3.14: Mean log abundance offish caught at the entrance, central and upper locations within each estuary. Lines denote standard error. 76
Figure 3.15: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Lake Illawarra over the three year sampling period. Lines denote standard error. 82
Figure 3.16: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of St Georges Basin over the three year sampling period. Lines denote standard error. 86 XVll
Figure 3.17: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Lake Conjola over the three year sampling period. Lines denote standard error. 89
Figure 3.18: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Burrill Lake over the three year sampling period. Lines denote standard error. 92
Figure 3.19: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Coila Lake over the three year sampling period. Lines denote standard error. 95
Figure 3.20: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Wallaga Lake over the three year sampling period. Lines denote standard error. 98
Figure 3.21: (A) Mean abundance (log (x+1)), (B) Mean number offish species, (C) Mean abundance of commercial fish, and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Merimbula Lake over the three year sampling period. Lines denote standard error. 101
Figure 4.1: Plots of multi-dimensional scaling based on fish communities caught during each sampling event at the entrance, central and upper locations within the six estuaries 119 XVIU
Figure 4.2: Two-dimensional plots of multi-dimensional scaling offish commimity Data for six estuaries, showing effects of seasons and years. Locations have been pooled. Sp=spring, su=summer, au=autumn, wi=winter. Numbers refer to each year of sampling. 121
Figure 4.3: Shade matrix for 56 species and 36 samples (separated on basis of location and sampling event) from Lake Illawarra. Abundance of species (double square root transformation from Bray-curtis similarity) has been categorised and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Increasing density shown by symbols • 0 O O • • 123
Figure 4.4: Shade matrix for 60 species and 36 samples (separated on basis of location and sampling event) from St Georges Basin. Abundance of species (double square root transformation from Bray-curtis similarity) has been categorised and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Increasing density shown by symbols • 0 O O • • 124
Figure 4.5: Shade matrix for 56 species and 36 samples (separated on basis of Location and sampling event) from Lake Conjola. Abundance of species (double square root transformation from Bray-curtis similarity) has been categorised and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Increasing density shown by symbols • © O O • • 125
Figure 4.6: Shade matrix for 53 species and 36 samples (separated on basis of Location and sampling event) from Burrill Lake. Abundance of species (double square root transformation from Bray-curtis similarity) has been categorised and represented by symbols of increasing density, and ordered XIX
on the basis of cluster analysis of species. Increasing density shown by symbols • 0 O O • • 126
Figure 4.7: Shade matrix for 41 species and 36 samples (separated on basis of Location and sampling event) from Coila Lake. Abtmdance of species (double square root transformation from Bray-curtis similarity) has been categorised and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Increasing density shown by symbols • 0 O O • • 127
Figure 4.8: Shade matrix for 52 species and 36 samples (separated on basis of Location and sampling event) from Wallaga Lake, Abundance of species (double square root transformation from Bray-curtis similarity) has been categorised and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Increasing density shown by symbols • 0 O O • • 128
Figure 4.9: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Lake Illawarra, Data was 4 root transformed. Stress = 0.17 131
Figure 4.10: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in St Georges Basin. Data was 4 root transformed. Stress = 0.17 132
Figure 4.11: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Lake Conjola. Data was 4*^ root transformed. Stress = 0.17 133 XX
Figure 4.12: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Burrill Lake. Data was 4*^ root transformed. Stress = 0.16 134
Figure 4.13: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Coila Lake. Data was 4* root transformed. Stress = 0.14 135
Figure 4.14: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Wallaga Lake. Data was 4*^* root transformed. Stress = 0.17 136
Figure 4.15: Two-dimensional plots offish assemblage data from the six estuaries. Separated into locations and seasonal samples. Blue represents entrance samples, orange the central samples and green the upper samples. 141
Figure 4.16: The number offish species found with increasing number of sites. Sites include the entrance, central and upper locations of the seven estuaries 148
Figure 5.1: Total number of individuals considered important to commercial and /or recreational fisheries, caught at each sampling event within the seven estuaries. Locations have been pooled, Merimbula sampled for two years only 174
Figure 5.2: Mean niunbers of juvenile Acanthopagrus australis captured at the entrance,central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled for two years. Data was log (x+1) transformed. Bars denote standard error. 179 XXI
Figure 5.3: (A) Size composition of Acanthopagrus australis caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Illawarra have been shown . 184
Figure 5.4: (A) Size composition of Acanthopagrus australis bream caught in Lake Conjola over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Conjola have been shown, 185
Figure 5.5: The number of Acanthopagrus australis bream at each 10mm length interval for the peak recmitment times in Coila Lake. 187
Figure 5.6: (A) Size composition of Acanthopagrus australis caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Wallaga Lake have been shown. 188
Figure 5.7: Mean numbers of juvenile Girella tricuspidata captured at the entrance, central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled for two years. Data was log (x+1) transformed. Bars denote standard error. 191
Figure 5.8: (A) Size composition of Girella tricuspidata caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Illawarra have been shown. 193
Figure 5.9: (A) Size composition of Girella tricuspidata caught in St Georges Basin over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within xxn
St Georges Basin have been shown. 194
Figure 5.10: (A) Size composition of Girella tricuspidata caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Wallaga Lake have been shown. 196
Figure 5.11: (A) Size composition of Girella tricuspidata caught in Merimbula Lake over the two-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Merimbula Lake have been shown. 197
Figure 5.12: Mean numbers of juvemle Meuschenia trachylepis captured at the entrance, central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled for two years. Data was log (x+1) transformed. Bars denote standard error. 200
Figure 5.13: (A) Size composition of Meuschenia trachylepis caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Illawarra have been shown. 202
Figure 5.14: (A) Size composition of Meuschenia trachylepis caught in St Georges Basin over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within St Georges Basin have been shown. 203
Figure 5.15: (A) Size composition of Meuschenia trachylepis caught in Lake Conjola over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Conjola have been shown. 205 XXlll
Figure 5.16: (A) Size composition of Meuschenia trachylepis caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Wallaga Lake have been shown. 206
Figure 5.17: Mean numbers of juvenile Monacanthus chinensis captured at the entrance, central and upper locations of the seven estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled for two years. Data was log (x+1) transformed. Bars denote standard error. 209
Figure 5.18: (A) Size composition of Monacanthus chinensis caught in St Georges Basin over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within St Georges Basin have been shown. 211
Figure 5.19: (A) Size composition of Monacanthus chinensis caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Wallaga Lake have been shown. 212
Figure 5.20: Mean numbers of juvenile Gerres subfasciatus captured at the entrance. Central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled for two years. Data was log (x+1) transformed. Bars denote standard error, 215
Figure 5.21: (A) Size composition of Gerres subfasciatus caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Illawarra have been shown. 216 XXIV
Figure 5.22: (A) Size composition of Gerres subfasciatus caught in Lake Conjola over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Conj ola have been shown. 218
Figure 5.23: (A) Size composition of Gerres subfasciatus caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Wallaga Lake have been shown. 219
Figure 6.1: Lake Illawarra, showing the 32 sampling sites within the eight zones (see Figure 1.1 for further information on location) 239
Figure 6.2: Durras Lake, showing the 32 sampling sites within the eight zones (see Figure 1.1 for further information on location). 240
Figure 6.3: The range of salinity values (parts per thousand) recorded at each of the thirty sites within (A) Lake Illawarra, and (B) Durras lake, from May 1999 to May 2000. Sites are labelled as in Figure 6.1 and 6.2. 242
Figure 6.4: Maximum and minimum temperatures (°C) at sites within (A) Lake Illawarra, and (B) Durras Lake, based on data during each sampling event from May 1999 to May 2000. Sites are labelled as in Figure 6.1 and 6.2. 243
Figure 6.5: Total nimiber of species caught at each site within (A) Lake Illawarra and (B) Durras Lake. Sampling events have been pooled. 249
Figure 6.6: Three-dimensional plots from the multi-dimensional (MDS) scaling analysis of the fish commimity data from Lake Illawarra showing the thirty-two sites sampled (as labelled in Figure 6.1). Sampling events have been combined and data has undergone (A) 4* root transformation (stress =0.15) and (B) XXV
presence/absence transformation (stress = 0.17). 251
Figure 6.7: Dendogram showing results of MDS classification, using abundance data For fish species caught in Lake Illawarra, between May 1999 and May 2000. Zones are shown with site numbers in brackets. Data has undergone a 4*^ root transformation, and sampling events have been pooled. 252
Figure 6.8: Dendogram showing results of MDS classification, using abundance data For fish species caught in Lake Illawarra, between May 1999 and May 2000. Zones are shown with site numbers in brackets. Data has undergone a presence/ absence transformation, and sampling events have been pooled. 253
Figure 6.9: Three-dimensional plots from the multi-dimensional (MDS) scaling analysis of the fish community data from Durras Lake showing the thirty-two sites sampled (as labelled in Figure 6.1), Sampling events have been combined and data has undergone (A) 4* root transformation (stress =0.15) and (B) presence/absence transformation (stress = 0.17). 261
Figure 6.10: Dendogram showing results of MDS classification, using abundance data For fish species caught in Durras Lake, between May 1999 and May 2000. Zones are shown with site nvunbers in brackets. Data has undergone a 4*'* root transformation, and sampling events have been pooled. 262
Figure 6.11: Dendogram showing results of MDS classification, using abundance data For fish species caught in Durras Lake, between May 1999 and May 2000. Zones are shown with site numbers in brackets. Data has undergone a presence/ absence transformation, and sampling events have been pooled. 263
Figure 6.12: Total number of commercial fish species caught at each site in (A) Lake Illawarra and, (B) Durras Lake, from May 1999 to May 2000. Sampling events have been pooled. Sites are labelled as in Figure 6.1 and 6.2. 265 XXVI
Figure 6.13: Total abundance of Acanthopagrus australis caught in Lake Illawarra during May, August and December 1999; and (B) corresponding mean fork length (mm) of individuals. Lines denote standard error, 269
Figure 6.14: Total abundance of Acanthopagrus australis caught in Durras Lake during December 1999; and (B) corresponding mean fork length (mm) of individuals. Lines denote standard error. 270
Figure 6.15: Total abundance of Girella tricuspidata caught in Lake Illawarra during October and December 1999; and (B) corresponding mean fork length (nmi) of individuals. Lines denote standard error. 272
Figure 6.16: (A) Total abvmdance of Girella tricuspidata caught within Durras Lake During December 1999 and Febmary 2000; and (B) corresponding mean fork Length (mm) of individuals during those periods. Lines denote standard error 274
Figure 6.17: Mean fork length (mm) of Rhabdosargus sarba caught at sites within Lake Illawarra during October 1999, December 1999 and May 2000. Lines denote standard error. 275
Figure 6.18: Mean fork length (mm) of Rhabdosargus sarba caught at sites within Durras Lake during December 1999. Lines denote standard error. 276
Figure 6.19: Monthly summaries of wind speed and direction for Lake Illawarra from May 1999 and May 2000. Data courtesy of Bureau of Meteorology, station no. 068228, Insufficient data was available for December 1999, 283
Figure 6.20: Simulated circulation pattems for common prevailing winds at Lake Illawarra (from Sherman et al. 2000), 284 xxvu
Figure 6.21: Monthly summaries of wind speed and direction for Dmras Lake from May 1999 and May 2000, Data courtesy of Bureau of Meteorology, station no. 069134. Only AM data available. 285 XXVlll
LIST OF TABLES
Table 3.1: Description of estuaries sampled in the three-year study offish commimities in shallow water seagrass habitats along the south-east coast of New South Wales. Data from West et al 1985, DLWC 2000) 53
Table 3.2: Fish species and overall total abundance offish captures from the seven estuaries sampled from October 1997 to July 2000. Locations and sampling events have been pooled. *indicates species considered to be commercially and/or recreationally important 70
Table 3.3: Results from multiple regression analysis offish species richness and abundance against environmental variables. For abundance log transformed values were used. The sign in brackets indicates the direction of the relationship. P<0.05*, P<0.01 **, P<0.001 ***. na indicates no variables significant 78
Table 3.4: Summary of analyses of variance for mean numbers of species for each individual estuary. Mean square vales are shown. L, location within estuary, SE, sampling event, d.f, degrees of freedom. P<0.01 *, i'<0.001 **. 81
Table 3.5: Summary of analyses of variance for mean numbers of individuals for each individual estuary. Mean square vales are shown. L, location within estuary, SE, sampling event, d.f, degrees of freedom. P<0.01 *, P<0.001 81
Table 3.6: Summary of analysis of variance for mean numbers of commercial and/or recreational fish species for each individual estuary. Mean square vales are Shown. L, location within estuary, SE, sampling event, d.f, degrees of freedom. P<0.01*,P<0.001**. 83
Table 3.7: Summary of analysis of variance for mean abundance of commercial and/or recreational fish species for each individual estuary. Mean square vales are XXIX
Shown. L, location within estuary, SE, sampling event, d.f, degrees of freedom. P<0.01*,P<0.001**. 84
Table 4.1: Dominant, typical and discriminating species in communities defined by similarities of shallow water fish samples from NSW south coast estuaries. Dominant species ranked by total abundance with cut-off at ~80% of total untransformed (raw) abimdance. Typical and discriminating species based on arbitrary cut-off values of percentage similarity (>6% and 5% respectively) in SIMPER analysis 143
Table 4.2: List of estuarine species considered rare, on the criteria of distribution and area of occupancy (<10% of all sites), from sampling of the estuaries studied 146
Table 5.1: The eight most abundant fish species (ranked), considered important to commercial and/or recreational fisheries, caught in the seven estuaries over the three-year sampling period 175
Table 5.2: Analysis of variance of the abundance of the five commercial fish species. Data has been log transformed. Mean square values are shown. Significance of the test is represented by P<0.01 *, P<0.001 **. 180
Table 5.3: Percentage variation in abundance of the five commercial fish species, explained by each term in the ANOVA model for each individual estuary 181
Table 5.4: Principal recmitment periods for five fish species caught in six estuaries of southeast Australia, over a three-year period, and for Merimbula Lake which was sampled for two years. 221
Table 6.1: List of fish species and number caught in Lake Illawarra, separated into the eight zones, during the sampling period from May 1999 to May 2000. Sampling events have been pooled. *indicates species of commercial and/or recreational significance 245 XXX
Table 6.2: List offish species and number caught in Durras Lake, separated into the eight zones, during the sampling period from May 1999 to May 2000. Sampling events have been pooled. *indicates species of commercial and/or recreational significance 257
Table 6.3: Total abundance of small juveniles and large juveniles of dominant commercial species caught in Lake Illawarra by zones, with site numbers given for each zone. Small juveniles are defined as those less than or equal to 40mm FL, Large juveniles are defined as greater than 40mm FL. Ocean spawners are denoted as (O). Lagoon spawners are denoted as (L), 267
Table 6.4: Total abundance of small juveniles and large juveniles of dominant commercial species caught in Durras Lake by zones, with site numbers given for each zone. Small juveniles are defined as those less than or equal to 40mm FL. Large juveniles are defmed as greater than 40mm FL. Ocean spawners are denoted as (O). Lagoon spawners are denoted as (L). 268 Chapter 1
Introduction
1.1 General Background
There are over 4200 fish species within the ocean, coastal shelf and estuarine environments of Ausfralia. Approximately 80% of these species are considered endemic to Australia waters (Pogonoski et al. 2002). Many hundreds of these species are associated with the estuaries and estuarine habitats of south-eastem Australia (Pollard et al. 1998).
Estuaries are highly productive areas that provide an important range of habitats and play an essential role in the life history of many freshwater, brackish and marine species of fish
(Haedrich 1983). Seagrass beds within estuaries are a particularly significant habitat for many species of fish, cmstaceans and invertebrates (Young 1981; Bell & Pollard 1989;
Szedlmayer & Able 1996). The relatively complex stmcture of seagrass canopies offer fishes protection from predation (Heck & Orth 1980) and shelter from strong tidal currents and water movements (Bell & Pollard 1989). Seagrass beds also offer a diverse supply of food resources, for example, a rich array small invertebrate species, preyed upon by many fish species (Pollard 1984). It is these factors that make seagrass beds a vital habitat in estuaries, particularly as a nursery area for juveniles of many marine and estuarine fish species (Blaber
1980; Potter et al. 1983; Bell et al 1984; Lenanton & Potter 1987; Whitfield et al 1989;
Potter et al. 1990; Ferrell & Bell 1991; Warburton & Blaber 1992; Blaber et al. 1995). Fish species in estuaries can be separated into three main groups based on their ability to breed within the estuarine environment. Firstly, there are those species that spawn in the ocean but whose larvae and juveniles enter estuaries primarily as a nursery area, and the second group consists of fish species which spawn within tiie estuary, and are often permanent residents of the estuarine habitat, and lastly there are the freshwaterspecie s that utilise the upper brackish and freshwaterreache s of estuaries (Whitfield 1998).
The relationship between the composition and abundance of fish communities and seagrasses has been investigated in many parts of the world (Bell «& Pollard 1989; Bennett 1989;
Whitfield et al 1989; Lubbers et al. 1990; Potter et al. 1990; Ayvazian et al. 1992; AH et al.
1996). For several estuaries in New South Wales (NSW), south-eastem (SE) Australia, studies have demonsfrated that larvae and juveniles of many species of fish settle from the water column into Zostera capricomi and Posidonia australis seagrass meadows (Pollard
1984; Bell et al 1987; Steffe 1991; Ferrell et al 1993). These seagrass beds are also home to a range of permanent residents, often small cryptic species such as hardyheads, gobies, perchlets and pipefishes (Pollard 1984). Generally, the species richness offish commimities and the abundance of particular fish species have been found to be high in seagrass beds, when compared to other nearby habitats, such as unvegetated sand habitats (Gray et al. 1996;
West & King 1996). While information is available concerning fish assemblages in seagrass meadows at some locations, almost no information is available for estuaries along much of the SE Ausfralian coast. Scientific sampling programs of estuarine fish communities in SE
Ausfralia have generally been restricted to a few localities and short time frames, usually for one or two years (Ferrell et al 1993; McNeill & Fairweather 1993; Pollard 1994a). Yet most of the estuaries in the region are harvested commercially (Gibbs 1997; NSW Fisheries 1997) and/or recreationally (West & Gordon 1994). The present study has examined the composition, abundance and distribution of fish communities found within eight estuaries along a 500km sttetch of coastiine, from Wollongong to Merimbula in SE Ausfralia (Figure
1.1). These estuaries were Lake Illawarra, St Georges Basin, Lake Conjola, Burrill Lake,
Durras Lake, Coila Lake, Wallaga Lake and Merimbula Lake. 1.2 Statement of the problem
Estuaries form an integral part of coastal environments, acting as interface between terrestrial, freshwater and marine ecosystems (Ketchum 1983). The estuaries, coastal lakes and lagoons of SE Ausfralia are widely recognised for thefr environmental qualities, heritage values, vulnerability and in some cases, their pristine aquatic communities (DEST 1996).
They are also a resource of significant value to both commercial and recreational fisheries
(Pollard 1981; NSW Fisheries 1997). The estuaries along the SE Australian coastline, south of Wollongong (34° 33'S, 150° 52'E), are particularly interesting in terms of fish communities as there are over 40 Intermittently Closed and Open Lakes and Lagoons
(ICOLLs) (West et al 1985; Williams et al 1998). However, in this region, as in other parts of the world, estuarine environments are increasingly under pressure. Environmental degradation is occurring due to housing developments, increased tourism and from the effects of damaged catchments (Meehan 2001). Conflicts are emerging over fishery resources, declining natural resources and threatened biodiversity (Healthy Rivers Commission of New
South Wales 2002). More importantiy, the nature of the estuaries in the SE Ausfralian region make them particularly vulnerable to degradation and environmental damage, as the majority of the estuaries are relatively small systems which close off to the sea for varying periods of time (West et al 1985). Despite these existing threats there is little information presentiy available to assist in the sustainable management of the fisheries, fishes and fish habitats in these estuaries (Healthy Rivers Commission of New South Wales 2002). For example, for most estuaries of SE Ausfralia there is no information pertaining to biodiversity of fish species. This study aims to improve our understanding of estuarine fish communities in SE
Ausfralia and to provide information essential for sustainable management. Specifically, the following questions were addressed: • What are the major species and families of fishes making up the estuarine fish
assemblages in shallow water seagrass beds in intermittently closed and open
estuarine systems along the SE Australian coastline?
• What large-scale and small-scale spatial and temporal variability occurs in the fish
diversity and abundance, and community compositions in this region?
• What are the major factors influencing these spatial and temporal pattems in fish
species diversity, abundance and community compositions?
• How should fish biodiversity information be used for the management of estuarine
environments?
In addressing these questions, the following gaps in present knowledge were identified.
1.3 Present gaps in knowledge
There is a distinct lack of information on fish species that inhabit SE Ausfralian waterways, and this is particularly tme for the majority of estuaries situated south of the Sydney region, and those in the far south of NSW. While there have been some studies on these fish communities, these have been very limited in terms of spatial and temporal scales. For the majority of estuaries in this region, the shallow water fish communities have never been sampled. Baseline information, even as basic as a list of fish species present in the estuaries, is essential in determining the importance of these estuaries to biodiversity conservation and sustainable management of fisheries. Up to the present time, any management decision conceming fish biodiversity has been based on best guesses (e.g., NSW Fisheries Office of
Conservation 2000). Thus, the first aim of this study is to gather biodiversity information on shallow water seagrass fish communities in as many estuaries as possible in the region south of Wollongong to the NSW/Victorian border.
Without baseline data, there is also no knowledge of spatial and temporal changes in the fish communities, for example, on a regional and local scale, and over a long period of time.
There is a lack of information conceming changes in community composition on a large spatial scale (regional differences among estuaries) and small scale (local differences within estuaries). Such information is essential for understanding how fish species utilise the estuarine environment along the southem NSW coastline, and particularly in intermittently closed and open lakes. Estuarine environments are driven by major processes, such as hydrological and morphological characteristics, and physical and chemical variables, such as salinity, temperature and turbidity, and fishes respond to these abiotic and biotic gradients that will vary between estuaries (Blaber & Blaber 1980; Loneragan et al. 1986a; Cyms &
Blaber 1987). There is little to no understanding of abundance and distribution pattems of fish species in intermittently closed and open estuaries of south-eastem NSW in response to such processes. For these ICOLLs with such little information, decisions for regional matters such as choosing estuaries for biodiversity purposes, are increasingly difficult and somewhat dubious (NSW Fisheries Office of Conservation 2000). Similarly, management decisions conceming local areas, such as zoning within estuaries (Healthy Rivers Commission of New
South Wales 2002) becomes arbifrary and based on the assumption that better studied locations are 'typical'.
The NSW coastline has been commercially harvested for fish resources for over 200 years, and today supports a viable commercial and recreational fishery (Gibbs 1997; NSW Fisheries
2002). Despite this, there is very little information on the recmitinent pattems of many important commercial species in this region. Moreover, there has been no attempt to quantify the use of seagrass habitats within intermittently closed and open lakes as sites for settlement and early development of many fish species.
Lastly, there has been an increasing interest in characterisation of fish communities and habitats, mainly due to the need to identify representative areas in order to implement marine reserves and conservation sfrategies. To date though, fish conservation has been concemed primarily with freshwater species, and there has been no application of the fundamental
concepts of conservation theories, such as rarity, diversity and commonness, to estuarine fish
communities in NSW. Moreover, as the basis of conservation theory has its roots in terrestrial research, investigations of whether they are applicable to the estuarine and marine
environment is needed.
Thus, from these gaps in knowledge the following objectives were developed.
1.4 Thesis Objectives
The primary objectives of this research were therefore:
1. To compare the large-scale and small-scale spatial and temporal variability on the
diversity and abundance of fish in seagrass beds, and where possible assess
environmental and physical factors that may be influential on variability pattems.
2. To assess the fish species compositions of seagrass habitats in ICOLLs of SE
Austtalia, and analyse large-scale and small-scale pattems in the assemblages within
and between estuaries.
3. To examine the frequency and timing of recmitment for a selection of economically
important fish species, and compare differences in recmitinent across several spatial and temporal scales; latitudinally, witiiin and between ICOLLs, and between seasons
and years.
4. To relate these findings to the conservation of biodiversity and the sustainable
management of the fisheries, fishes and fish habitats of the region.
This research is primarily based on two sampling programs carried out in the SE Austtalian region. The first involved sampling three locations within seven estuaries along a 500 kilomefre (km) stretch of the SE Australian coastline, every quarter for three years. These data were used to investigate spatial and temporal variability and fish community stmcturing over large spatial scales. It also provided new information on the timing and sfrength of recmitment of many fish species, including some of economic importance. The second sampling program involved intensively sampling 32 sites within two estuaries, every few weeks over 12 months. These data provided detailed information, at a local scale, on variability and abundance, and community stmcturing, particularly in relation to changes in the local environment.
1.5 Thesis Structure
This thesis is composed of seven chapters.
In Chapter One, a general background to the estuarine environment and fish communities in south-eastem NSW has been given. The remainder of this Chapter will provide details of the study region and the estuaries sampled.
Chapter Two is a preliminary review of relevant literature and research. It is concemed with such aspects as the influence of environmental and physical parameters on pattems of estuarine community fish stmcture and the recmitment dynamics of marine and estuarine fish species. Additional literature has been discussed in each chapter where requfred.
Chapter Three presents pattems of distribution and abundance of shallow water seagrass fish communities in seven estuaries. These estuaries were sampled quarterly for three years. This chapter is mainly concemed with large-scale pattems of diversity and abundance, within the estuaries and among them. The estuaries sampled in this research program were Lake
Illawarra, St Georges Basin, Lake Conjola, Burrill Lake, Coila Lake, Wallaga Lake and
Merimbula Lake, This chapter meets Objective 1,
In Chapter Four, the stmcture of the fish communities in these seven estuaries has been investigated. This chapter will examine changes in the fish assemblages within the estuaries and among them, and how the stmcture of the fish community changes between seasons and years. Such information is important not only to understand the dynamics of the fish communities in these estuaries, but also to understand what the south coast fish fauna is comprised of, in order to investigate natural fluctuations in fish community change and assess the impact of anthropogenic change in the future. This chapter meets Objective 2.
In Chapter Five, the recmitment pattems of major commercial fish species are investigated from the seven estuaries. Localised and regional variability in the strength and timing of recmitment are discussed, as are mechanisms that could be responsible for recmitment variability offish species along the south coast of NSW. This Chapter meets Objective 3.
Chapter Six presents results from an intensive spatial and temporal study of the fish communities of two ICOLLs; Lake Illawarra and Durras Lake. This chapter investigates further how fish species use seagrass beds around the whole perimeter of these estuaries, in particular as nursery areas. This Chapter contributes to Objective 1 and 2. Chapter Seven presents the major conclusions from this research, and how they relate to current and future management of the estuaries in SE Australia, and, more generally, tiie conservation planning for the region. Recommendations for future research are also discussed. This Chapter meets Objective 4.
1.6 Characteristics of Study Region
In this section some general characteristics of the region and the estuaries sampled have been presented (Figure 1.1)
1.6.1 Climatic conditions
In these studies, fish communities in estuaries along the coastline between Wollongong to
Merimbula, NSW have been investigated (Figure 1.1), The climate of the Wollongong region is characterised by warm summers, with average summer (Febmary) maxima and minima temperatures 27°C and 17°C respectively, and mild winters (July) with average maxima temperature of 17°C and minima of 8°C, Further south, near Merimbula, the temperatures are milder, with a reported summer (Febmary) average maxima of 25°C and minima of 15°C. Average winter temperatures are also cooler with a winter (July) maxima and minima of 16°C and 4°C respectively (Bureau of Meteorology 2002),
Sea surface temperatures change latitudinally along the NSW south coast. Near Sydney the average ocean temperatures range from a minima of 17,7 °C to a maximum of 23.5 °C, while further south (Batemans Bay) the average sea surface minima temperature is 16.3 °C and the maxima 19,5 °C, Within the estuaries, though, water temperatures often extend outside this range, witii reported summer water temperatures reaching 25°C and in winter falling to approximately 10°C (Directorate of Oceanography and Meteorology 2002), Rainfall is evenly 10
100 km I Lake N Illawarra
NEW SOUTH 1 WALES 35'00' St Georges Basin Lake Conjola T.r.opic.qf.Capricorn.. Burrill Lake Durras Lake Batemans Bay Coila Lake
Wallaga Lake
Pacific Merimbula Lake Ocean
Figure 1.1: Map of study region in southeast New South Wales, showing the eight estuaries included m the research program. 11 distributed throughout the year along the southem coastline of NSW. Annual precipitation near Merimbula is about 820mm per year and near Sydney it is slightiy higher with approximately 1000-1200mm per year, based on long-term averages (Bureau of Meteorology
2002).
1.6.2 Coastal environment
The coastline of SE Australia is primarily an embayed bedrock coastline characterised by a narrow discontinuous plain (Roy 1984). The estuaries in NSW were excavated into bedrock by rivers during a period of lower sea level. In southem NSW, the estuaries are located landward of sand barriers deposited during the post-glacial marine fransgression, approximately 6000-7000 years ago (Thom & Roy 1983), and the majority of these estuaries are permanently or intermittently open and closed to the ocean (West et al. 1985). Tidal inlets have formed as a consequence of sand accumulation and are described as systems with dynamic entrances (Roy 1984), Along the NSW coastline there are also open embayments, which are seaward of these sand barriers, and these systems have permanently marine conditions (e,g,, Jervis Bay). The coastline is subject to approximately 2m tides and has a wave-dominated climate (Roy 1984).
1.6.3 Study Sites
Research was carried out in eight ICOLLs in southem NSW. A brief description of these study sites is included below.
Lake Illawarra
Lake Illawarra is a shallow coastal lagoon located approximately 8 kms south of Wollongong
City (34° 33'S, 150° 52'E). The lake drains a catchment of approximately 270 km^ with a
3 0009 03317226 8 12 surface water area of 36.3 km^ (DLWC 2000), The lake is a large shallow depression, with an average depth estimated at 1,9 m and a maximum depth of 3,7m (Harris et al 1980). It is estimated that a quarter of the lake is less than 1,2m deep (Yassini & Clarke 1986),
Lake Illawarra is classified as a barrier lagoon that is intermittently open (Roy 1984). The entrance closed at least twenty times in the period from 1920 to 1973, but has remained open from that time on. A permanent enfrance was constmcted at the opening of Lake Illawarra in
2000, (after the end of this study), with the aim of increasing tidal exchange of the lake and improving water quality (ERM Mitchell McCotter and Associates Pty Ltd 1994). Lake
Illawarra is a poorly flushed system with small tidal exchange. On average there is a discharge of approximately one million cubic meties, which results in a tidal range of 0.03m
(DLWC 2000). Wind is regarded as the main mechanism for mass water movement within the lake, but wind, tides, stieam discharges and currents caused by large floods also contribute to water circulation. The lake surface often becomes turbulent with wave heights of up to 0.5m, due to the north-south orientation of the lake exposing it to stiong southerly and south-westerly winds. Studies of Lake Illawarra have given estimates of the efficiency of the enfrance exchange of 30%. That is, 30% of the tidal inflow remains in the lake, while
70%) is unmixed and flows back to the ocean on the ebb tide (Eurobodalla Shire Council
2001). Lake salinity is mainly governed by the influx of freshwater through rainwater, mnoff and via creeks. Previous studies have found that salinity varies from about 13 to 31 parts per thousand (ppt), and due to the vertical mixing caused by wave action, there is generally no salinity sfratification (Ellis et al 1977).
The principal creeks that feed into the lake are Macquarie Rivulet, Mullet Creek, Duck Creek and Hooka Creek. All are situated in the westem side of the lake. The catchment of Lake
Illawarra is dominated by urban and industrial land uses, disturbed freehold and leasehold
(non-urban) land. The shoreHne is highly developed, with less than 25% in a natural 13 condition (Bell & Edwards 1980). Land-use pattem around the perimeter of the lake has a direct impact on water quality, including an increased amount of urban runoff carrying significant amounts of nifrogen and phosphoms, suspended solids and other pollutants
(Yassini & Clarke 1986). High turbidity levels are a common feature in Lake Illawarra, due to the shallowness of the lake and the effects of wind and wave action (DLWC 2000).
The lake has approximately 5,1 km'^ of seagrass beds, comprising of Zostera capricomi,
Ruppia megacarpa and Halophila spp. (decipiens and ovalis) (West et al 1985). The annual commercial fisheries production in Lake Illawarra, based on statistics from the Estuary
General Fishery during the 1999/00 period was 138, 223 kg. The main finfish species caught were Mugil cephalus, Platycephalus fuscus, Gerres subfasciatus and Hyporhamphus melanchor (NSW Fisheries 2001a).
St Georges Basin
St Georges Basin (35° 12'S, 150° 35'E) is located approximately 200 kms south of Sydney.
The lake has a catchment area of 390 km^ and water area of 42 km^ (DLWC 2000). It is classified as a barrier lagoon that remains open to the sea. The inlet into this lake is known as
Sussex Inlet, and is 6.4km in length and on average 150m wide for its entire length (Sinclair
n
Knight and Partners 1981). The estuary contains approximately 8.5 km of seagrass area that contains Zostera capricomi, Posidonia australis, Halophila spp. and Ruppia spp. (West et al.
1985).
St Georges Basin has low to moderate catchment use and disturbance, with approximately
50-70%) of continuous shoreline in natural condition (Bell & Edwards 1980). Land uses surrounding the basin include; freehold land. Crown land, urban and industiial, and national park/nature reserve exists on one small section of the lake. Extensive clearing of freehold 14 land is of concem and may impact on the lake's water quality in the future (Bell & Edwards
1980), Sussex Inlet at the lake's entrance has developed into a tourist and amateur fishing
centre and the lake is known for excellent recreational boating, thus puttmg substantial pressure on the lake in peak summer times (Bell & Edwards 1980),
During the period 1999/00 the commercial fisheries catch from the Estuary General Fishery
was 112,048 kg, with the major finfish species caught being bream {Acanthopagrus australis
and Acanthopagrus butcheri), Gerres subfasciatus, Myxus elongatus and Girella tricuspidata
(NSW Fisheries 2001a),
Lake Conjola
Lake Conjola (35° 16's, 150° 30'E) is located lOkms north of the township of Ulladulla. It is
classified as a barrier lagoon, which has little infilling and is intermittently open/closed. Its
catchment area is 145 km^, with the area of water being 5,9 km^. The lake has approximately
0.5 km of seagrass area, which is dominated by Zostera capricomi and Halophila spp. (West
et al 1985). The commercial fisheries production for the period 1999/00 was 14,138kg, with
the major species caught from the Estuary General Fishery being, Mugil cephalus, Sillago
ciliata, Gerres subfasciatus and bream {Acanthopagrus australis and Acanthopagrus
butcheri) (NSW Fisheries 2001a).
Lake Conjola is a popular tourist and holiday destination, with caravan parks, urban and industrial land uses situated at the enfrance and middle reaches of the lagoon. These activities have resulted in deterioration of the water quality in the lake, mainly due to septic overflows.
On the eastern side of the lake, there is a large fract of natural bushland situated on Crown
Land (Bell & Edwards 1980), and the upper catchment is contained within the McDonald
State Forest (DLWC 2000). 15
Burrill Lake
Burrill Lake (35°24'S, 150°27'E) is situated approximately 4kms southwest of tiie township
of Ulladulla. It is a barrier estuary connected to the ocean by a narrow, shallow inlet channel
of approximately two kilomefres in length. The area of water is 4.206 km and the catchment
area is 78 km^. The lake basin is reasonably deep and the maximum tidal range in the area is
reported to be 1,8m. The entrance to Burrill Lake is predominantly open, and has become
fully closed only once in the last 25 years. There is often great community pressure to dredge
the channel area as the enfrance does become choked with marine sands. The last dredging
activity was undertaken in 1996 (DLWC 2000).
n Burrill Lake has a seagrass area of approximately 0.5 km and contains Zostera capricomi
and Halophila spp. (West et al 1985). The total commercial fisheries catch from Burrill
Lake was 11,726 kg during the period 1999/00, The major components of the finfish catch
were Girella tricuspidata, Hyporhamphus regularis, Gerres subfasiatus and Mugil cephalus
(NSW Fisheries 2001a),
The enttance of Burrill Lake is surrounded by urban and industrial land uses, predominantly
coastal holiday development on the coastal fiinges. Land use around the lake is
predominantly farming in the Milton area. Forestry operations occur in the Woodbum State
Forest, which surrounds the southem and westem shores of the lake. According to Bell &
Edwards (1980), 50 to 75% of the catchment has been cleared, and the shoreline has been
developed in the range of 25 to 50%, 16
Durras Lake
Durras Lake (150 °19'E, 35 °38'S) is a shallow branching lake, with a waterway area of 35 km^ draining a catchment area of 55 km^ (DLWC 2000), It is located to the north of
Batemans Bay, and has two townships, Durras Lake and North Durras located south and north of its enfrance respectively. The enfrance is intermittently closed and open, and is
located shoreward of a nearshore reef, which offers protection from ocean waves and beach building processes (DLWC 2000),
Durras Lake has been recognised for its conservation attributes, largely as a result of its
catchment and shoreline still being in a high natural state. Approximately 78%) of the
catchment is State Forest, 1% Murramarang National Park, 5% Crown Land and the
remaining freehold. Three major creeks and several minor sfreams fed into the lake.
Benandarah Creek and Bridge Creek flow in from the Sate Forest to the south, and
Ryans/Cumbralaway Creek enters the lake at its north-west comer (DLWC 2000).
Durras Lake has a distinct slow rate of exchange between lake and ocean waters, with the
freshwater input into the lake considered low. The salinity levels at the mouths of the
tributary creeks are typically 18 to 25 ppt (DLWC 2000). While this is regarded to have a
significant effect on the estuarine fauna, there has been little study on the fish communities
inhabiting the lake. A preliminary aquatic fauna survey of Durras Lake and its catchment by
the Austialian/New Guinea Fishes Association revealed what may be a new species of
Rainbow Fish (Ausfralian/New Guinea Fishes Association 2001).
Durras Lake has 0.5 km of seagrass habitat, mainly Zostera capricomi with some Halophila ovalis. The lake also has significant saltmarsh and wetland areas (West et al 1985).
Commercial fisheries production for Durras Lake was 9,214 kg during 1999/00, with the 17 major finfish species being Mugil cephalus, Girella tricuspidata and Platycephalus fuscus
(NSW Fisheries 2001a).
Coila Lake
Coila Lake (36°02'S, 150°08'E) is sittiated 325 kms south of Sydney. It is classified as a coastal lagoon with little infilling, Coila Lake is unusual in that the lake size is large compared to its catchment. The waterway is approximately 7km^ compared to a catchment area of 48 km . The small catchment means freshwater flows are generally unable to maintain an open entrance for any period of time. Ocean swell condition is the other main factor that initiates entrance closure. Moderate swells over a period of greater than four days can result in a spit formation across the entrance (DLWC 2000). Under natural conditions the enttance would probably remain closed for lengthy periods but it is usually mechanically opened when the water level rises and floods a caravan park at its head. From the period
March 1975 to November 1999, seventeen recorded opening events have occurred, of which only four of those were natural. At times when the enfrance is opened and the only substantial creek feeding the lake, Coila Creek, is not in flood, the salinity of the water is similar to the ocean over the entire lake. The lake is large in size, but overall it is a shallow waterway with depths not exceeding 3m (Eurobodalla Shire Council 2001).
The lake has a water area of 9 km and a seagrass area of 1.862 km , which is comprised of
Zostera capricomi and Halophila spp. The commercial fisheries production of Coila Lake for the 1999/00 period was 41,888 kg, Rhabdosargus sarba was the major species caught
(15, 643 kg), with bream {Acanthopagrus australis ducA Acanthopagrus butcheri) and Girella tricuspidata also being caught (NSW Fisheries 2001a), 18
The hoHday resort of Tuross Heads is close to the enttance of Coila Lake, which is a popular recreational area in the summer months. The land use surrounding the rest of the lake is dominated by disturbed freehold and leasehold land (Bell & Edwards 1980), Bell & Edwards
(1980) classified the lake as having moderate to high disturbance and use, with only 25 to
50%) of the shoreline in natural condition,
Wallaga Lake
Wallaga Lake (36°22'S, 150°05'E) is sittiated 375 kms south of Sydney, It is classified as a coastal barrier lagoon with little infilling. The lake is intermittently open/closed and is also mechanically opened at times. Closures recorded since 1957 have been during 1972, 1982 and 2000, Some areas in the upper reaches are apparently affected by poor flushing, but the majority of Wallaga Lake has good horizontal and vertical water exchange due to persistent
2 low speed winds and tidal exchange (DLWC 2000). It has a catchment area of 285 km and a water area of 7,805 km (West et al. 1985). The seagrass beds comprise an area of 1.343 2 km , and contains species of Zostera, Halophila and Ruppia. For the 1999/00 period, commercial fisheries production was 32, 787 kg, with bream {Acanthopagrus australis and
Acanthopagrus butcheri), Girella tricuspidata, Platycephalus fuscus, Mugil cephalus and
Gerres subfasciatus being the major finfish species caught (NSW Fisheries 2001a).
Wallaga Lake has a depth of between 3 and 6 m, with a maximum depth of 8m at the centre of the lake. The tidal limit is approximately at 10 km from the entrance. The lake has small inputs of fresh water from a number of creeks, mainly Narira and Dignams Creek. Some degree of vertical salinity sttatification occurs within the lake, with salinity varying from 25 ppt at the surface to over 30 ppt at the bed (DLWC 2000). 19
Wallaga Lake has a shoreline of more than a 100 kms, of which Wallaga Lake National Park occupies the westem and southem shoreline. Agriculture and grazing account for over half
of the area of the lake's catchment, and it is estimated that 6\% of the catchment has been
cleared for agricultural and urban purposes since European settlement Water quality has
been perceived as good but there are concems as a result of development, septic tank
overflows, tourism and overfishing. Analysis has shown that the majority of the nutrient load
on Wallaga Lake comes from agricultural areas (DLWC 2000).
Merimbula Lake
The most southem lake in this study is Merimbula Lake (36°54'S, 149°55'E), which is
situated 455 kms south of Sydney. It is a barrier estuary with a permanently open enttance to
the sea, by the presence of constmcted training walls. It has a catchment area of 48km and a
water area of 4.6km . A 250m long causeway and bridge is present across the inlet, and offer
considerable resistance to tidal penefration. Mean lake level is superelevated 0.25m above
mean sea level (DLWC 2000). The lake contains extensive areas of seagrass, covering an
area of approximately 2.3 km . Posidonia australis is the dominant seagrass species;
however, other species recorded include Zostera capricomi, Zostera mulleri, Ruppia spp. and
Halophila ovalis (West et al. 1985).
Merimbula is a seasonal holiday destination with urban and industrial land-uses located at the
enttance of the lake. Bell & Edwards (1980) estimated that 50-70%o of the catchment has
been cleared with shoreline development in the range of 75-100%. Merimbula Lake supports
substantial oyster production as well as finfish. No fisheries statistics are available for the
period 1999/00, but tiie commercial fisheries production for the 1995/6 period was 141
054kg/yr (NSW Fisheries 1997), 20
Chapter 2
Literature Review
2.1 General Introduction
This chapter presents an overview of general literature relevant to the research objectives.
More specific literature related to each topic has been presented in subsequent chapters.
The high biological productivity of estuaries worldwide and the value of different habitats to fishes and fisheries resources is well documented (Lenanton & Potter 1987; Ayvazian et al
1992; Wantiez et al 1996; Brazner & Beals 1997). There have been many studies investigating the estuarine fish community of Austtalia and these have included descriptions of different species and assemblages offish that are typical of different habitats or areas of an estuary. For example, research has been conducted on fish associated with seagrass (Scott
1981; Middleton et al 1984; Bell & Pollard 1989), mangroves (Bell et al 1984; Laegdsgaard
& Johnson 1995), bare sand areas (Ferrell & Bell 1991; Connolly 1994; Gray et al 1996) and deeper water areas (Loneragan et al 1986b; Bell et al. 1992). In Australia, ecological research of fishes has focused on temperate estuaries in Westem Australia (Lenanton &
Potter 1987; Potter & Hyndes 1999), Victoria (Connolly 1994; Edgar & Shaw 1995a; Edgar
& Shaw 1995b), and the ttopical estuaries in Queensland (Blaber et al 1989; Warburton &
Blaber 1992; Sheaves 1996). In NSW, the majority of estuarine fish research has been confined to the large permanently open estuaries, such as the coastal rivers of the northern area of the state (Gray et al 1996; West & King 1996; West & Walford 2000), and embayments in the Sydney Basin region (Bell et al 1984; Ferrell & Bell 1991; McNeill et al
1992b; Worthington et al 1992b). Detailed studies of fish populations have also been undertaken in some southem NSW locations, such as Jervis Bay, and several estuaries along 21 tiie NSW south coast (Ferrell et al 1993; McNeill & Fafrweather 1993), and Botany Bay
(Belle? a/. 1984; Worthington e? a/. 1992b), Several ofthese major studies have been carried out in response to the assessment of potential environmental impacts of major developments in coastal regions, such as extensions to Sydney Airport adjacent to Botany Bay (Bell et al
1984; Worthington et al 1992b), and development of naval port facilities in Jervis Bay
(Ferrell et al 1993; McNeill & Fairweather 1993),
Thus, although the composition of fish assemblages in estuarine environments at many specific locations around Ausfralia has been relatively well researched, little data is available conceming fish diversity, abundance and community pattems for the south coast and far south coast of New South Wales, The south coast of NSW consists of approximately sixty coastal waterbodies, the majority of which are small Intermittently Closed and Open Lakes and Lagoons (ICOLLs). Apart from the commercial fishing statistics, which are available for many of these lakes, there is little data available for a significant portion of the estuarine environment along the NSW coastline, and the importance of ICOLLs to marine and coastal fishes, particularly in terms of recmitment, remains poorly understood.
2.2 The estuarine environment of NSW
Along the coastline of NSW, there are approximately nine hundred waterbodies, ranging from large coastal lagoons that are permanently or periodically open to the ocean, to small ephemeral creeks (Williams et al 1998). In the present study, the definition of an estuary by
Day (1981a) is adopted, namely that an estuary is "a partially enclosed coastal body of water which is eitiier permanentiy or periodically open to the sea and within which there is a measurable variation of salinity due to a mixture of sea water with fresh water derived from land drainage". Existing classification schemes dealing with estuaries of NSW have relied on two processes, namely the basic geological type and the stage that the estuary has reached in 22
terms of its evolutionary development (Roy 1984). On this basis, Roy (1984) has classified
estuaries into four distinct types:
Type 1: Drowned river valley - having full tidal exchange
Type 2: Barrier estuary - having attenuated tides
Type 3: Saline coastal lagoon - having ephemeral enttances and usually no tides
Type 4: Open embayment
Estuary types can further be described in terms of their evolutionary development (after (Roy
1984)):
A = little infilling { youthful } to D = very infilled { mature }
The NSW coastline has been divided into three very broad regional units on the basis of such
factors as estuary type (Roy 1984) and commercial fishing statistics (Pease 1999), influence
of the East Ausfralian Current (Oritz 1994; Pollard et al 1998) and oceanographic data for
areas adjacent to the coast (CSIRO Division of Fisheries and Oceanography 1997). The
estuaries of NSW fall into three main latitudinal regions, the northem, centtal and southem
groups, with the principal determinants being estuary size, enttance depth and width,
catchment area and geomorphologic type (Pease 1999).
In the northem region of NSW, the majority of the estuaries are drowned river valleys and
riverine barrier estuaries. The cenfral region is characterised by drowned river valleys that
have permanentiy open enttance channels, a full tidal range and sub-aqueous tidal deltas.
(Roy 1984). The centtal and southem regions also have large barrier lagoon estuaries.
Barrier estuaries along the NSW coast occur behind sand barriers and vary greatiy in size. 23 from less than lOkm^ to more than lOOkm^. These barrier estuaries typically have narrow entrance channels within extensive tidal and backbarrier sand flats. The tidal range is attenuated to a degree determined by the channel morphology and the size of the enttance relative to the estuary (Roy 1984), Thus, those barrier estuaries with long, narrow enttance channels and large mud basins, such as St Georges Basin have a low tidal range, while others such as Merimbula Lake, have a large tidal range due to a wide enttance channel and small mud basin (Bega Valley Shire Council 1997),
The southem region is also characterised by ICOLLs, These saline coastal lakes can at times be separated from the sea by a sand barrier making them non-tidal (Roy 1984), Heavy rains or storm waves may be sufficient to breach the bar, returning the lakes to tidal estuaries.
The barrier estuaries of southem NSW have several characteristics that make them typically different to estuaries situated in the northem and centtal regions. The south coast barrier estuaries are commonly small (40km to less than 10km ), have narrow enttance channels, are only weakly tidal, and have limited freshwaterinput . The salinity regime of the north and central coast estuaries is primarily influenced by tidal circulation, and high river flow discharge, often resulting in salinity gradients both horizontally and vertically. Those along the south coast have wind induced currents and are often well-mixed water bodies (Roy
1984). The intermittent open and closed nature ofthese estuaries is a natural process, and this regime of opening and closing to the ocean can be on a cycle of a few months to several years, depending on climatic conditions.
Within the estuaries of NSW, there are seven species of seagrass; Posidonia australis,
Zostera capricomi, Zostera meulleri, Heterozostera tasmanica, Halophila ovalis, Halophila decipiens and Ruppia spp, (West et al 1985), The most widespread species in NSW are
Zostera spp. and Halophila spp., and they are both distributed in ICOLLs. P. australis is 24 restticted in its distribution in NSW to permanently open estuaries, favouring high salinities and low nutrients (West et al 1985), After settlement from the planktonic larval stage, post- larval fishes typically spend the ffrst few months of their life in Z. capricomi seagrass beds, before migrating to altemative habitats such as deeper water or Posidonia meadows
(Middleton et al 1984; McNeill et al 1992b; Warburton & Blaber 1992; Worthington et al
1992b). As this study is concemed with the role of the estuaries of southem NSW as nursery
areas, sampling was concenttated in Z. capricomi beds, which have previously also be shown
to contain estuarine resident species (Middleton et al 1984; Bell & Pollard 1989).
2.3 Factors influencing fish community structure
Estuaries are characterised as a mixing zone where marine and freshwaterwater s meet, where
there are significant environmental gradients, and often high levels of primary and secondary
production (Ketchum 1983), These characteristics have a pronounced effect on the diversity,
abundance and biomass of fishes that are able to live in these environments (Ketchum 1983;
Whitfield 1998). Fish distribution and abundance in estuarine habitats are determined principally by physical and chemical factors such as salinity, temperature, tidal currents and
winds, and then by biological factors including reproduction, predation, competition and
habitat selection (Blaber & Blaber 1980; Whitfield et al 1989).
2.3.1 Biological factors
The high productivity of estuaries is a clear reason why fish species utilise these
environments as nurseries, with detritus- and phytoplankton-based food webs important to many fish species (Haedrich 1983). Thus, the emphasis is upon feeding and growth, and the habitats within estuaries provide excellent opportunities. The high level of available food sources allows initial rapid growtii of new recmits, which enables them quickly to attain a 25 size that make them less susceptible to predators (Kennish 1990). The fish assemblages in estuaries are also ch^acterised by a low number of large carnivorous fish, compared to tiie open marine environment, and it is believed that predation on small juvenile fish will be lower in estuaries, and thus thee habitats offer a sanctuary from predation for young-of-the year fish (Blaber & Blaber 1980). The higher diversity of abundance of fishes inhabiting seagrass beds, compared to other habitats, such as bare subsfrata, is often related to the physical complexity of seagrass canopies (Orth et al. 1984). Some studies have suggested that variations in seagrass stmcture, such as shoot length and leaf density, will influence the abundance of fish present, through increased protection from predators and reduced predator efficiency (Orth et al. 1984; Bell & Westoby 1986a). However, very few studies have shown correlations between seagrass complexity and the abundance of fishes (Adams 1976; Heck &
Orth 1980; Stoner 1983). Bell & Westoby (1986b) posttilated that there may be correlations between physical complexity of seagrass and the abundance of juvenile fish within individual seagrass beds, but not on a wider scale across a range of seagrass beds. This led to the development of the "stay and settle" model (Bell & Westoby 1986b), where it is argued that fish settling from the plankton do not discriminate between beds of differing physical complexity, but will settle in the first available shelter they encounter. Juveniles are also unlikely to move between seagrass beds or re-enter the plankton to search for more complex habitat, as it involves a greater risk of predation. Worthington et al. (1991) also found evidence to support the hypothesis that fish larvae do not discriminate between differing leaf densities at settlement. An experiment with artificial seagrass units (ASU) testing the effects of seagrass densities on the settlement of fishes, suggested that larvae can discriminate between no shelter (bare subsfrata) and shelter (seagrass), but could not discriminate between high and low densities of seagrass stiiicture (Worthington et al 1991). 26
It has been suggested that the distribution of juvenile fish in estuaries cannot solely be explained by biological factors, such as food resources, predation pressure, and protection due to the complexity of the seagrass canopy (Blaber & Blaber 1980). A number of physical factors must also play an important role in the distribution of juvenile fish in estuaries, such as tidal currents, water movements and salinity, which in tum has an effect on the reproductive behaviour of many fish species that utilise estuaries during part of their life cycle.
2.3.2 Physical and chemical factors
Estuaries are complex and dynamic systems with highly variable environments. Parameters such as salinity, temperature and turbidity can vary greatly through time, and between locations. The effects of environmental variables in stmcturing fish communities has been examined by a number of researchers (Loneragan et al. 1986a; Robinson & Tonn 1989;
Brazner «fe Beals 1997). In permanently open estuaries there are distinct longitudinal gradients in environmental variables, such as salinity and turbidity, which leads to differences in the fauna and flora along the estuarine gradient. Research conducted on tidal dominated estuaries has thus resulted in two important conclusions conceming fish distribution and community stmcture in estuarine environments. Firstly, fish community stmcture differs along an estuarine gradient, as the environment changes from marine dominated conditions to tiie freshwater zone (Loneragan et al 1989; Sheaves 1998; West & Walford 2000).
Secondly, that factors such as salinity, turbidity and temperature are important influences on community sttiicture (Blaber & Blaber 1980; Loneragan et al 1986a; Cyms & Blaber 1987).
Turbidity has been found important in influencing the distiibution and abundance of estuarine fish communities (Cyms & Blaber 1987; Hayes et al 1992). ft has been suggested that juveniles are attracted to shallow ttirbid waters (Blaber & Blaber 1980), possibly due to 27 reduced predator efficiency and increased feedmg success in more turbid waters (Whitfield
1998). Growth rates of juvenile estuarine fish have been positively correlated with water temperature in some estuarine habitats (Wortiiington et al 1992b; Jenkins et al 1996).
Diversity of fish species is reported to decline in an upstteam direction in some permanently open estuaries with salinity gradients (Blaber et al 1989; Loneragan & Potter 1990; Sheaves
1998). Indeed many fish have been categorized into groups on the basis of levels of salinity tolerances and life history strategies (Lenanton & Potter 1987; Loneragan et al 1989; West &
King 1996; Blaber 1997; Sheaves 1998). The influence of salinity on estuarine fish communities has been investigated widely and the distribution of marine and estuarine species has often been related to salmity and distance from the estuary mouth. For example, the range in which stenohaline marine species will proceed into an estuary and their survival is often limited by salinity (Young et al 1997). Some species are able to tolerate large fluctuations in salinity (Blaber 1973) and can therefore capitalize on any opportunity to exploit the protective and productive environment provided by estuaries (Blaber 1987; Potter
& Hyndes 1994; Young et al. 1997). For example, some Mugilidae species are euryhaline
(Blaber 1987) and will remain in an estuary when salinities are low. Species from the
Gobiidae family, such as Psuedogobious olorum and Favonigobius lateralis, can survive in salinities ranging from 1 to 35 ppt, and hence are euryhaline species (Potter & Hyndes 1999).
However, it is reported that long periods of estuary closure and declining salinity is particularly sttessful to marine species (Blaber & Whitfield 1976; Whitfield et al 1981) and osmoregulatory sfress could result in mortality and lower species diversity (Bennett 1985;
Pollard 1994a). Mass mortality of marine species occurred in the Bot River estuary (southem
Afiica), when salinity declined dramatically after a long period of enttance closure (Bennett
1985). Therefore, one reason for longitudinal differences in species richness and biomass are differing species resilience and preferences for salinity levels. 28
Roy (1984) mfroduced the concept of entrance morphology playing a pivotal role in determining the hydrological conditions of NSW estuaries, and hence affecting the stmcture of biological communities that exist in these environments. The physical characteristics of the enttance to an estuary determine the tidal prism, degree of tidal exchange and the salinity regime within an estuary (Roy 1984). Many studies have demonsttated that salinity regime is a principal determining factor in the distribution of estuarine flora and biota, such as saltmarshes and mangroves and fransient fauna, which spend part of their life cycle in estuaries (Loneragan et al. 1986b). In permanently open estuaries, there are distinct longitudinal gradients in envfronmental variables, such as salinity and turbidity, which then leads to differences in the fauna and flora along the estuarine gradient. Also, research conducted on the variation among different habitat zones within an estuary have shown there is often clear spatial pattems of distribution and abundance; where species richness, overall abundance and biomass declines with distance from the estuary mouth (Loneragan et al.
1986a; Loneragan et al 1986b; Robertson & Duke 1990; Sheaves 1998). This pattem has often been related to the effects of the estuarine salinity gradient limiting some fish species distribution within an estuary and/or the lack of ocean-spawned larvae in the fish assemblage.
Ichthyoplankton assemblages in temperate estuaries typically contain species that breed within these systems as well as marine visitors. The seasonal variations in fish species composition and abundance is often due to fish species that breed in the ocean and whose larvae enter estuaries where they remain from a few months to a few years (Blaber & Blaber
1980; McNeill et al 1992a). The lack of ocean-spawned larvae far from the entrance in many estuarine systems is often related to water movements within estuaries. The major water movements will either be tidal currents or wind induced currents. Wind can generate water currents in shallow water and dictate the direction of surface fransport of materials.
Young et al (1997) and Hannan & WilHams (1998) both suggest that declines in fish 29 biodiversity, density and biomass in the shallow water seagrass habitats with increasing
distance from the estuary mouth, is correlated to the fact that the enfrance area is dominated by the larvae and juveniles of species which have entered from the ocean. In intensively
flushed, macro-and mesotidal estuaries, larvae utilise passive or selective tidal ttansport for
movement into the estuary and subsequent ttansport and retention within the system.
However, bar-built and barrier island estuaries, such as ICOLLs, are usually poorly flushed
and micro-tidal (<2m tidal range). Along the southeast coast of Austtalia, the most important
processes influencing the entry of marine larvae to estuaries are the use of flood tides, or the
accumulation of larvae within the frontal regions and tidal water plumes (Steffe 1991;
Kingsford & Suthers 1994; Gray et al 1996). Larvae are retained within the estuary by
rapidly settling along the shallow shoreline or on the bottom where water movements are
reduced (Whitfield 1998).
It has been suggested that limited penefration of recmits into upstteam areas explain reduced
diversity and abundance in these areas. The morphological and hydrological conditions of an
estuary will also determine the extent of larval intmsion into upstteam areas. For example,
Miskiewicz (1987) found water movements within Lake Macquarie (NSW) inadequate to ttansport competent ocean-spawned larvae upstteam. Conversely, West & King (1996) found as many newly recmited Acanthopagrus australis in Zostera capricomi beds approximately 35kms upstteam as they did in similar habitat lOkms from the mouth of the
Clarence River, NSW. This indicated that sttong tidal water movement in coastal rivers can ttansport larvae far distances upstteam to suitable habitats (West & King 1996; Hannan &
Williams 1998). In other estuarine envfronments the distance from the sea coupled with weak intemal currents in will limit tiie recmittnent of marine-spawned individuals far from the enfrance region (Whitfield 1998). 30
2.4 Life history categorisation of fishes in estuaries
The use of estuarine envfronments by fish has been categorized by a number of workers, commonly by the way in which fish species utilize estuaries for parts of their life cycle and the degree of which their survival is dependent on the estuary (Wallace et al 1984; Lenanton
& Potter 1987; Whitfield 1994). On a basic level, fish can be divided into four main ecological groupings; marine species, estuarine species, freshwater species and catadromous species (Whitfield 1998). A further division of these groupings concems primarily marine and estuarine species and relates directly to the concept of dependence on the estuarine environments for at least one stage of their life cycle, usually as a nursery or spawning ground, and for without which a viable population would cease to exist (Lenanton & Potter
1987; Blaber et al. 1989). The most commonly used categorizations are marine stragglers, estuarine opportunist and estuarine dependent (Wallace et al 1984; Lenanton & Potter 1987).
Some researches have further explored these categories.
For example, Whitfield (1994) developed an estuarine classification system for South African fishes with five major categories, which also had two to three divisions within each category.
Generally though, marine sfragglers are marine species, which occur irregularly and in low abundance in estuaries, and hence are not dependent on estuaries for their survival. There has been much debate over the terms estuarine dependent and estuarine opportunist, mainly due to the degree of which a species is actually dependent on an estuary for survival (Lenanton
1982). There are fish species that spend their whole life cycle within estuaries and thus these species would be considered estuarine-dependent. The debate arises from consideration of euryhaline marine species, which usually breed at sea with the juveniles showing various degrees of dependency on habitats within estuaries. Several authors have made the observation that juveniles of the "estuarine-dependent" species are also frequentiy abundant in protected inshore marine environments, and hence should be considered "estuarine- 31 opportunisf species (Hedgpeth 1982; Lenanton 1982; Lenanton & Potter 1987). The ability to categorise fish species relies on detailed studies on the biology of fish species, such as what has occurred in south-western Ausfralian estuaries over the last 20 years (e.g., Chubb et al 1981; Potter et al 1983; Prince & Potter 1983; Loneragan et al 1989; Hyndes et al 1992;
Young et al 1997). The categorisation of marine species as estuarine dependent can also be highly dependent on local situations, such as the availability of altemate protected marine habitats. In south-western Ausfralia, the presence of flinging limestone reefs has provided altemative habitats for many species that also use estuaries (Lenanton 1982), while in SE
Ausfralia, estuaries are considered to provide the principal nursery habitat (Pollard 1981).
Caution also needs to be taken when attempting to ttansfer the life-history of a species in a biogeographical area to a different area. For example, Urocampus carinostris is considered solely estuarine in south-westem Austtalia, but in SE Ausfralia it is also found in coastal marine waters (Howard & Koehn 1985).
The absence of detailed information on the life history of many of the marine and estuarine species in the waters of SE Austtalia (NSW Fisheries 2002; Pogonoski et al. 2002) makes decisions of the contributions of the various life-cycle categories to the estuarine fish communities difficult. Also, there has been no work in SE Austtalia to quantify if estuarine- associated species utilize other inshore marine environments as nursery areas. Hence, the assessment of the relative dependence of these species on estuaries as nursery grounds are a practice of best guesses.
2.5 Intermittently Closed and Open Lake and Lagoons (ICOLLs)
Research conducted on bar-breached and seasonally closed estuaries in Westem Australia and Soutii Africa have shown tiiat fish assemblages are influenced by the opening and closing regime; in particular tiie duration and size of the opening in the estuary mouth (Bennett 1989; 32
Whitfield 1989). The regime of opening and closing of the enttance influences pattems of recmitment for marine species and hence the composition and distributional pattems of the
fish assemblage in tiie esttiary (Potter et al 1990; Whitfield & Kok 1992; Potter & Hyndes
1994). The most obvious result of a closed estuary mouth is that it blocks recmitment of juveniles from marine waters and the emigration of subadults/adults from the estuary. The
composition of the fish fauna may be then dominated by estuarine and freshwater species,
with marine migrants contributing little to the fish community composition (Bennett 1989).
Species diversity has been shown to be lower in ICOLLs compared to permanently open
systems (Potter & Hyndes 1994; Whitfield 1994; Pollard \994a). Lenanton & Hodgkin
(1985) found the number offish species doubled in the Beaufort Estuary (Westem Austtalia),
when the entrance opened and suggested that the state of the enfrance mouth is probably the
single most important factor affecting fish species diversity. Others have suggested that the
variability in physical and chemical parameters of ICOLLs are stressful to biological
communities, and hence a less diverse biota will be present (Bennett 1985; Blaber 1987)
However, Whitfield (1998) has suggested that this presumed link between high fish diversity
and entrance conditions, can lead to an under emphasis of the importance of ICOLLs as
nursery areas, when compared to permanently open systems. Juveniles that enter systems
that subsequently close may have greater protection from predators due to elevated water
levels and lower numbers of large predatory fish. Aquatic plant and invertebrate food
resources also increase when estuaries are closed to the ocean, and as a consequence fish
growth rates may be higher (Whitfield 1980).
The intermittentiy open and closed lagoons of SE Austtalia are characteristic of high-energy
coastlines, similar to many estuaries in Soutiiem Afiica (Day 1981b; Bennett 1985), Mexico
(Yanez-Arancibia 1985) and soutii-westem Ausfralia (Potter et al 1983; Loneragan & Potter
1990; Potter «fe Hyndes 1999). Pattems of salinity, circulation, and flora and fauna are a 33 result of the interaction of past geological forces which have conditioned the shape and size of the estuary basin, and present processes of river discharge, tidal exchange and oceanographic events that bear influence on estuary hydrodynamics and biota (Roy et al.
2001), The conditions of the south coast estuaries are conttolled by enttance morphology that govems tidal exchange, and by the lack of a sttongly developed regional and seasonal pattem in rainfall. This conttasts sharply with estuaries in south-westem Ausfralia where
environmental conditions and the resultant fish community stmcture are influenced heavily by a characteristic seasonal rainfall pattem (Loneragan & Potter 1990; Potter & Hyndes
1999).
The variability of environmental parameters will also be influenced by the relatively small
size of the estuaries in SE Ausfralia. From Wollongong to the Victorian border there are
approximately 44 estuaries that cover a total area of only ISlkm"^ (West et al 1985). There is
also limited freshwater input into these systems, mainly through small creeks, and thus the
salinity regime is greatly influenced by enfrance morphology (Roy 1984). Coupled with a
small tidal range (<2m), the estuaries are therefore more often well-mixed. Little
hydrological information is available for the majority of these estuaries but data for three
estuaries along the NSW south coast (Pollard 1994b) revealed that salinity sfratification was
virtually non-existent within these estuaries. The majority of previous research of estuary
fishes has been conducted in estuaries where there were significant horizontal gradients in
surface salinity. Comparisons between these tidal estuaries and ICOLLs in terms of the effect of parameters, such as distance from the estuary mouth and the influence of the estuary gradient on pattems of juvenile flsh distribution, are difficult to make. Understanding juvenile fish distribution within ICOLLs is essential for placing a relative value on these habitats as nursery areas and tiierefore for the management ofthese environments. 34
Thus, the need for baseline studies in ICOLLs and small barrier estuaries of the south-coast of NSW are required firstly to describe fish species diversity in this region to develop greater understanding of the dynamics ofthese estuaries and thefr fish assemblages. This information is required to determine natural rates of variability in communities to assess changes over time from natural variability to those caused by anthropogenic activities. There is also a need to provide recmitment data for management of fisheries resources and to assess the relative importance of the south coast estuaries to fishery stocks in the region.
2.6 Recruitment of marine fish species
Recmitment in this study is defined as the addition of the young-of-the-year individuals from the pelagic habitat measured at some arbitrary time after larval settlement, adopted from
Connell (1985). Variable recmitment is a well-known phenomenon for populations of marine species that have pelagic, widely dispersed larvae (Houde 1987; Roughgarden et al.
1988; Underwood & Fairweather 1989). Determining the pattems of natural variability in recmitment, and the causes and consequences of this variability has become a centtal problem in fisheries biology (Fairweather 1991). The dynamics of recmitment are affected by physical and biological processes that occur both prior to and after the settlement of larvae
(Jones 1990; Doherty & Fowler 1994). For example, the wide dispersal of larvae can lead to high levels of mortahty (Sano 1998), and shortly after settlement, biological factors such as competition and predation can also greatly affect population size (Houde 1987; Kingsford
1992; Connell 1996). Processes in the pelagic stage of many marine species can lead to a lack of direct relationship between the size of the spawning stocks to the degree of recmitment to a local population (Gaines & Roughgarden 1985; Robertson et al 1993), and contiibute to large spatial and temporal variability in recmitment pattems (Underwood &
Denleyl984). 35
The majority of research on tiie relative contributions of recmitment mortality or growth to the demography and abundance of marine populations has focused on benthic invertebrates
(Caffey 1985; Connell 1985; Gaines & Roughgarden 1985; Underwood & Fairweather 1989).
It has been generally concluded that recmitment-limited populations are a result of a lack of pelagic propagules. However, it has been shown that for some temperate reef fish, egg and
larval abundance mostly show no correlation with juvenile fish density (Sissenwine 1984;
Levin 1996). Research on several fish species in the Caribbean (Robertson 1992) and the
Great Barrier Reef (Williams & Sale 1981) suggest that pattems offish recmitment are good
indicators of earlier pattems of settlement (Levin 1996). However, post-settlement processes
have the ability to uncouple original settlement pattems and recmitment (Ault & Johnson
1998), and thus would lead to spatial variability amongst zones and estuaries. This has been
shown for juvenile coral reef fish. For example, Connell (1996, 1997) found variation among
zones in predator abundance and rates of mortality of juvenile damselfish. Kingsford (1992)
demonsttated significant variation in the distribution, abundance and feeding habits of juvenile coral ttout species in the Great Barrier Reef Thus, while the importance of the
larval life-history stages for temperate fishes is recognised (Gray 1993; Gray & Miskiewicz
2000), studies on juvenile recmitment pattems (i.e,, post settlement) are also critical to the
understanding of factors affecting recmitment and the relationship to adult populations
(Munro & WilHams 1985; Doherty & WilHams 1988; Sale 1990).
An understanding of recmitment pattems in determining the stmcture of fish communities
requires consideration of communities and recmitment over a wide range of spatial and
temporal scales (WilHams & Sale 1981; Gaines & Roughgarden 1985; Doherty & Williams
1988; Underwood & Fairweather 1989). At large spatial scales, mechanisms responsible for variation in tiie delivery of pelagic larvae are related to stochastic oceanographic events, and recmits characteristically arrive in irregular pulses or episodic events (Levin et al 1997). At 36 small spatial scales pattems of recmitment reflect interaction of nearshore oceanic events such as currents and eddies, and biotic processes such as larval behaviour, competition and predation (Kingsford et al 1991; Fowler et al 1992). Hence, multi-scale studies on recmitment are required to investigate natural rates of variability and processes that contribute to natural fluctuations in fish populations.
The number of studies which have provided a comprehensive recmitment information for estuarine fish communities in Austtalia, over numerous spatial scales and across a number of years, is exttemely limited. Few studies have identified large-scale regional variation in recmitment by simultaneously comparing recmitment across a number of estuaries, and incorporating small-scale variations by studying habitat zones within the estuaries.
2.7 Recruitment of temperate fish to estuarine seagrass meadows
The majority of studies focusing on settlement of fishes in temperate Austtalian estuaries have been conducted within seagrass beds. Seagrass beds in the shallow fringes of estuaries are important in their fiinction as nurseries for many species of fish and cmstaceans, and support species valuable to commercial and recreational fisheries (Pollard 1984; Bell &
Pollard 1989; Loneragan et al. 1990; McNeill et al. 1992b). Seagrasses provide shelter from predators due to their relatively complex stmcture, and are an enhanced substrate for food items (Pollard 1984). Larvae of different species will often settle in different parts of an estuary due to factors, such as location of species spawning areas, salinity and temperature tolerances of eggs, and the behaviour of larvae (Bell et al. 1988). It is believed that the distribution pattems resulting from these processes will be maintained as larvae will settle in the first suitable seagrass habitat encountered (Bell et al 1988), and juveniles less than 40mm in lengtii are unlikely to move between seagrass patches (Middleton et al 1984; Bell &
Westoby 1986b). Thus habitat location is often a more important influence than habitat 37 stmcture. In a series of studies, Bell et al. (1988) found that seagrass patches located throughout an Austtalian estuary were all significant collectors of recmiting fish and different species recmited into different parts of the estuary. Other studies have also shown that characteristics of seagrass habitat, such as density of seagrass shoots, does not appear to account for sites having high recmitment (McNeill et al. 1992b), and that larvae will recmit both to natural seagrass areas and to artificial seagrass units (Bell et al 1988).
Despite large variations in recmitment events for many marine species, spatial pattems of consistent settlement have been documented (Jones 1984), and particular sites may receive a large supply of larvae that enables a high level of recmitment. In a study of recmitment in
Botany Bay, McNeill et al (1992) found there was consistently high recmitment of several commercial fish species to seagrass beds at one particular site. Areas that consistently have high recmitment have also been recorded for rocky-reef invertebrates and coral reef fish
(Jones 1984; Doherty & WilHams 1988; Underwood & Fairweather 1989). This finding has implications not only for the management of the fish populations but also for the habitat in question.
For the NSW south coast, there is a scarcity of information conceming recmitment events for many fish species. Despite long established fishing grounds in the estuaries and oceans of this region, natural fluctuations in recmitment are partially understood for only a few of the major commercial species harvested. Information on the pattems of estuarine recmitment by marine fish larvae along eastem Austtalia is available (Miskiewicz 1987; Bell & Pollard
1989; McNeiH et al 1992b; Worthington et al 1992a), but it is particularly scarce south of tiie Sydney region. Research to determine natural rates of fish recmitinent to the south and far south coast estuaries of NSW, and to assess the relative importance ofthese estuaries as nursery habitats has been recommended as an essential component of an ecosystem-based management plan for fisheries resources (Fairweather & McNeill 1993). 38
With the recent inclusion of ecological based management, fisheries management is meant to incorporate an understanding of the entire migration cfrcuit (Fairweather 1991). This involves distinguishing spawning grounds, nursery areas and adult stocks. Seagrass beds in estuaries are known to be essential nursery areas for the maintenance of many commercially harvested species in coastal and estuarine waters in NSW (Pollard 1984). Arrival of recmits may provide one of the best early pictures of the condition of stocks and also give early waming signs of environmental condition (Fairweather 1991). The literature on reef species have indicated that recmitment pattems are one of the principal determinants of spatial and temporal pattems of adult numbers of marine organisms (Gaines & Roughgarden 1985;
Doherty & WilHams 1988; Roughgarden et al 1988; Booth & Brosnan 1994; Doherty «&
Fowler 1994; Caley et al. 1996). How this would apply to temperate estuarine and coastal species in southem Austtalia is relatively unknown. The main difference is that individuals recmiting to coral reef systems often remain in that habitat as adults, whereas the seagrass beds in estuaries are used primarily as a ttansient nursery habitat for many commercially harvested species. Nevertheless, protection of this habitat should increase survival of individuals at a critical stage in their life history and thus have the potential to increase the
5ield of adult fisheries.
2.8 Sampling of estuarine fish communities in shallow water seagrass habitats
Coastal lakes contain a variety of habitats used by fish, including shallow and deep waters, and different species and different size ranges of fish will utilise these different habitats. This study concenttates on shallow water habitats, and in particular the sample regime is focused on seagrass areas.
The most commonly employed techniques for sampling estuarine fish communities is by the use of nets, poisons, baited fish ttaps and visual detection, hi the present sttidy, the adopted 39 method needed to meet certain criteria, such as; being easy to deploy, able to be replicated and relatively non-destmctive. These criteria immediately eliminated the use of poisons, such as rotenone due to high mortality of the fish communities (Bell et al 1978). Poisons are also impractical for sampling ICOLLs, as whilst the enttance is closed, there is a lack of the tidal flow and dilution needed to remove the poison from the site. Rotenone can be a threat to the researcher (Gray & Bell 1986),
Sampling with fish traps is often deployed in areas where there are many submerged obstmctions, such as a mangrove forest (Sheaves 1992). However, ttaps have many selectivity biases. The type of bait used greatly influences the species to be caught (Whitelaw et al. 1991). Factors such as the size of the ttap mesh, size and number of openings to the trap, and soak time all influence the size, number and type of fish species caught (Whitelaw etal 1991).
Visual observation is a quick and cost effective method, but there are several problems associated with the method. The accuracy of species identification is quite variable, especially for small juveniles of similar groups (e.g., tarwhine, bream and snapper), and would most likely depend upon the ability and experience of the researcher. Also as most of the lakes in SE Austtalia often have turbid water conditions, this would hinder the applicability of this method. A recent study investigating the use of video sampling of shallow water seagrass habitats in Lake Illawarra found fewer species could be detected by visual video surveys, compared to netting methods (Hindmarsh 2002).
The use of a seine net was therefore considered one of the best options. The type of nets that have been used include seine nets, beam ttawls, pop nets and gill nets. The type of habitat to be sampled, and the area and depth of water will often determine which net can be employed.
Seine nets have been used in many estuarine fish sampling programs (Pollard 1994a; Gray et 40 al 1996; West & King 1996; Hannan & WilHams 1998), and are especially effective for sampling shallow water habitats. A comparative study of fish sampling methods in Lake
Illawarra found that a large seine net (6mm sttetched mesh, 12m long) was able to detect a higher number of species and individuals when compared to a small seine net (225mm'^ mesh,
5m long) and traps (Antoniou 1997). The main advantages of this type of net are; that it is
easy to deploy, requires only two people, is relatively inexpensive, has low fish mortality,
and, has low impact on seagrass habitats (Clark et al 1994). A fine mesh size (usually 6nim
stretch mesh) will be selective for small juveniles, with sub-adults and adult fish rarely
caught by this method (West & King 1996).
2.9 Management and Conservation of Estuaries
Since the signing of the International Convention on Biological Diversity, Austtalia has had
an obligation to protect and conserve biological diversity (Anon 1996). In respect to the
marine environment, the conservation and management of biological resources has been a
slow and ad hoc process (McNeill & Fairweather 1993). It is increasingly being recognised
that understanding the complex dynamics of marine and coastal ecosystems is essential for
management within an ecologically sustainable framework to be effective (Fairweather &
McNeill 1993). As this awareness grows across all sectors of management, from State
government agencies to resource-based industries, so does the realization that there is a great
lack of ecological knowledge to make informed decisions. An increase in research and
monitoring of coastal ecosystems is urgently required (Ward et al 1998; Fairweather 1999).
The limited understanding of the processes and elements of ecosystem fiinctioning in these
esttiarine environments means that placing a value on these ecosystems is difficult and often based on highly simplistic observations (Ward 2000). 41
2.9.1 Conservation status of estuarine species and issues of rarity
The current status of knowledge conceming the conservation status of estuarine fish in NSW
is relatively poor (Pogonoski et al 2002). The majority of conservation theory has been
developed from terrestrial systems and the applicability of ttansferring the criteria for
assessment of the conservation status of marine taxa may not be appropriate (Allison et al
1998; Chapman 1998; Chapman 1999). There is currently inadequate knowledge of the rarity
of estuarine species and about the measures of rarity that are suitable for marine taxa
(Chapman 1999). There is a general scarcity of studies on rarity in marine organisms, but
recently it has received some attention for coral reef communities (Hawkins et al 2000), and
for individual fish species (Morris et al. 2000). Threats to marine and estuarine habitat,
conservation status of species, issues of rarity, commonness and diversity are all factors that
need to be addressed for effective conservation of marine biological diversity. In freshwater
systems these issues have received much attention and have been investigated through
measures such as the Index of Biological Integrity (Karr 1993). In Austtalia, the freshwater
fish fauna is relatively well documented and studied (Gehrke & Harris 2000) and established
indexes of the conservation status of freshwater fishes exist. In confrast, fish species
inhabiting estuarine environments in temperate Australia have received little attention. It is
only in the last few years that concem has been raised about the vulnerability, population
levels and threatening processes of a few key species (Pogonoski et al 2002). Species placed
on the endangered species list in NSW are the eastem freshwater cod, green sawfish, grey
nurse shark, Murray hardyhead, Oxleyan pygmy perch, river snail and frout cod (NSW
Fisheries 2003a). Of these species, only the green sawfish occurs in estuaries (NSW
Fisheries 2003a). There are several reasons why the conservation status of estuarine fish
species in temperate AusttaHa has received little attention, hi Austtalia, long-term datasets needed for evaluation of rarity are available only for coral reef species, namely in the Great 42
Barrier Reef (e.g., WilHams & Sale 1981; Fowler et al 1992; Auft «fe Johnson 1998), and for fish communities in the estuaries of south-westem Austtalia ( e,g., Chubb et al 1981; Potter et al 1983; Prince & Potter 1983; Loneragan et al 1989; Hyndes et al 1992; Young et al
1997). Lastiy, and most importantly the lack of estuarine species on the threatened species lists could be related to the lack of long-term biological and ecological research that has been conducted on estuaries in NSW.
In other countries, particularly South Afiica, there has been much attention paid to the conservation planning and biodiversity of estuarine environments (Day 1981b; Whitfield
1998; Turpie et al 2000). In Austtalia, such attempts have been largely confined to
Tasmania (Edgar et al 2000). For similar outcomes in temperate Australia a systematic research effort is required to develop the baseline data of marine biodiversity needed to develop comprehensive coastal inventories. These data are urgently needed to form the basis of the estabHshment of marine protected areas (ESAC 1996; DEST 1999).
2.9.2 Marine Protected Areas
Delineation of Austtalia's coastal and marine environment into biogeographic regions was an objective of Ocean Rescue 2000, a marine conservation program by the Commonwealth government (Anon 1998). Ocean Rescue 2000 led to the Interim Marine and Coastal
Regionalisation for Ausfralia (IMCRA) and to the division of the NSW coast into five bioregions, distinguished by biological and physical characteristics (Thackway & Cresswell
1998). The present study encompasses two ofthese bioregions, with Lake Illawarra located in the southem exttemity of the Hawkesbury Shelf bioregion (which extends from Port
Stephens to Shellharbour), and the other estuaries located in the Batemans Shelf bioregion
(which extends from Shellharbour to Tathra). A process of selecting estuarine protected areas in the Batemans Shelf bioregion for inclusion in the National Representative System of 43
Marine Protected Areas (NRSMPA) has been undertaken by NSW Fisheries (NSW Fisheries
2001b). Geomorphological type of the estuary and degree of maturity was used for the determination of "comprehensiveness" and "representativeness", on the basis that the ecology of an estuary is largely dependent upon the geomorphological stage of an estuary (NSW
Fisheries 2001b). Despite the acknowledged importance of biodiversity information, fish communities and other taxa representing biological diversity have yet to be included in frameworks set out to select marine reserves along the NSW coastline.
In Tasmania and northem NSW the reserve selection procedure is heavily dependent on habitat mapping and protecting representative habitats (Barrett et al 2001, Avery in prep.).
The use of habitat types and geomorphology as a surrogate for biological diversity is undoubtedly due to the distinct lack of detailed knowledge of the ecological processes, particularly for estuaries in southem NSW. There is a considerable danger in only using selected physical features for the identification of a set of sites to represent the range of features designated for protection. The non-inclusion of biological diversity and ecological processes in the selection process can lead to the non-representativeness of habitat protection that has highlighted the previous ad-hoc procedure for selection of MP As in Austtalia
(McNeill 1994). It also does not reflect an understanding of the processes stmcturing these systems to ensure long-term ecological viability (Allison et al 1998).
The information gained from this present study, particularly on fish biodiversity, distribution and abundance pattems, and fish community ecology will be a valuable contribution to the knowledge base of estuarine biodiversity in SE Austtalia, and should assist in the sustainable management of the regions fish communities. 44
2.9.3 Monitoring of Estuarine Health
Fish communities have been suggested as one type of envfronmental indicator to describe
major ttends and impacts on estuarine, coastal and marine ecosystems (Ward et al 1998).
Fish populations fulfil some of the extensive properties that Ward et al. (1998) suggest SoE
indicators should display, namely being: capable of providing statistically verifiable and
reproducible data to show frends over time; cost-effective to allow regular monitoring with
ease; applicable to large regions; and able to provide early waming signs. Fish populations
also reflect a highly valued aspect of the environment as they are of economic value to
commercial and recreational fisheries, and have a high public value. Hence the monitoring of
fish communities in seagrass beds has relevance to policy and management needs.
Sampling of fish in seagrass habitats is also advantageous as there is generally higher
diversity and abundance of fishes in seagrass beds compared to unvegetated areas (see Bell
and Pollard 1989 for review). This has been attributed to the stmctural complexity of the
seagrass habitat providing protection from predators, shelter and more food resources
(Summerson «fe Peterson 1984; BeH «& Pollard 1989; McNeiU et al 1992b; Worthington et al
1992a). However, bare habitat can also support large densities offish (Ferrell & Bell 1991;
Gray et al 1996) and the many discrepancies in diversity and abundance of fish between
habitats seems to be due to many species consistency occur in only one habitat (Gray et al
1996). The general association of particular species with either seagrass or sand has been
documented in many estuaries in NSW (Gray et al 1996; West & King 1996). Thus it is
expected that that fish highly associated with sand habitat such as the muglids and sillaginids
would not be caught in this study. Seagrass beds though harbour many economically
important species and a high diversity of non-commercial species including a number of
permanent residents (Pollard 1984; Bell & Pollard 1989). In addition, the seine net used for
sampling shallow water habitats is relatively quick and easy to use, and most notably 45 produces reproducible and representative data. These qualities make this particular method
(see Chapter 3 for details) usefiil in the inclusion of a long-term program for monitoring the health of estuarine environments. The data produced from the present three-year research program will evaluate the usefulness of sampling shallow-water seagrass fish communities for a monitoring program, and make conclusions regarding the conservation status of estuarine fish communities in southeast NSW. 46
Chapter Three
Large-scale spatial and temporal variability in species diversity and
abundance of fish communities from south-eastern Australian estuaries
3.1 Introduction
The temperate south-east coastline of Australia, south of the Sydney Basin to the Victorian border has over sixty coastal waterbodies, and is dominated by barrier estuaries and saline coastal lagoons (West et al 1985). Many of these estuaries are termed Intermittently
Closed and Open Lakes and Lagoons (ICOLLS) due to the nature of the entrance mouth to become closed to the ocean for periods that can last from a few weeks to several years.
The fish fauna of the majority of the more than 40 coastal lakes along the south coast region, has not been documented, except for Lake Conjola, Swan Lake and Wollumboola
Lake for (Pollard 1994a), and Wagonga Inlet (McNeiH «fe Fairweather 1993),
ICOLLs have particular environmental and management issues directly resulting from their geomorphic character and enttance morphology (Roy et al 2001). The south coast estuaries are commonly small (10km to 40km ), have narrow entrance chaimels making them weakly tidal (when open) and small catchments resulting in limited freshwater input
(Roy 1984). These factors contribute to their sensitivity to natural and anthropogenic disturbance. Due to public pressure, these lakes are commonly artificially opened to alleviate flooding, improve water quality or in an attempt to increase prawn and flsh recmitment. Despite these management concems there has been little effort to gather relevant information, such as flsh species diversity and abundance, which might influence decision making (Healtiiy Rivers Commission of New South Wales 2002) An understanding of such ecological factors needs to be developed to supply the baseline data 47 which can be used in estuary management plans, State of the Envfronment reporting, ecosystem-based flshery management plans and to investigate the environmental impacts of fishing (ESAC 1996; DEST 1999).
In many regions of the world, the high biological productivity of estuaries is well documented (Ketchum 1983; Whitfield 1998), as is the value of different habitats to fishes and fisheries resources (PoHard 1984; Lenanton & Potter 1987; Whitfield et al 1989;
Ayvazian et al 1992; West 1993; Blaber 1997). Seagrasses in the shallow fiinges of estuaries are particularly important as they represent nursery areas for a number of marine teleosts and euryhaline fish species that are of significance to commercial and recreational fisheries, and are a habitat for permanent estuarine residents (Pollard 1984; Bell & Pollard
1989; Loneragan et al 1990; McNeill et al 1992). Physiological tolerance to parameters such as salinity, temperature, turbidity plus differing life history sttategies determine how fish species respond to habitat heterogeneity and dynamics (Blaber & Blaber 1980;
Whitfield et al 1981, Yanez-Arancibia 1985, Loneragan & Potter 1990; West & King
1996; Sheaves 1998). Research conducted on the variation among these different habitat zones within an estuary has often shown a clear spatial pattem in distribution and abundance of fishes; where species richness,overal l abundance and biomass often declines with distance from the estuary mouth (Loneragan et al. 1986b; Humphries et al 1992;
West & King 1996; Hannan & WilHams 1998). This has often been related to the effects of the estuarine salinity gradient, the physical impacts of water movements such as currents and tides and/or the decreased prominence of ocean spawned fish in the fish assemblage. Hence, it is likely that the distinct geomorphology and hydrological conditions of the intermittently open estuaries in south-eastem Australia will have important consequences for the structure of fish communities in this region, however little information is presently available 48
One of the objectives of this research was to compare large-scale and small-scale spatial and temporal variability on the diversity and abundance of fish (see pg. 6), and to assess whether species diversify and abundance pattems are similar to other estuarine environments in NSW. To achieve this objective, this chapter describes a sampling program of seven ICOLLs over a three-year period. The extensive data set generated from this sampling program has provided the first comprehensive assessment of estuarine fishes
in the region. This Chapter provides an analysis of intra- and inter-differences in estuary
fish diversity and abundance and quantifies the influence of regions within the selected
estuaries across several spatial and temporal scales. Also, as very few studies have been
conducted over such a large spatial scale of SE Austtalia, I have also investigated
differences in species diversity among estuaries and presented fish biodiversity
information on a biogeographic scale. The sampling sfrategy was specifically designed to
catch new recmits and juveniles in shallow water seagrass habitats, as this habitat is well documented as an important nursery area and a habitat for permanent estuarine resident
species. These baseline data will be essential for the development of long-term monitoring programs, for example as indicators of estuary health, and for the sustainable management of fishery resources. Later chapters will further describe these data, with emphasis on pattems in species assemblages (Chapter 4) and recmitinent pattems of commercially significant fish species (Chapter 5). In any large-scale study, it is important to determine the efficiency and optimum sampling design, particularly in terms of replication. For this reason, a short pilot study has been carried out to consider the statistical power of the proposed sampling program. 49
3.2 Pilot Study
3.2.1 Introduction
Background
A pilot study was undertaken to determine the optimum number of replicates needed to
provide adequate statistical power for the fish sampHng program. Power is defined as the
probability of rejecting the null hypothesis. Previous studies of shallow water fish that
have sampled habitats with similar fine mesh seine nets have either three (Gray et al.
1996) or four (FerreH & Bell 1991; McNeiH et al 1992; West & King 1996) repHcates per
"sample". The importance of optimising the replication and ensuring suitable statistical
power is now recognised as an important step in the planning stages of a sampling program
(Peterman 1990; Taylor & Gerrodette 1993). In many studies, conclusions about the
presence or absence of an environmental impact or change in the abundance of a
population is based only on whether a statistically significant change has been detected.
However, in many instances it is essential to ensure there were specific testable hypotheses
and an appropriate sampling design and replication. The development of an experimental
design should include a power analysis to determine the minimum number of samples that
are required to detect given magnitude changes in the fish population.
For the pilot study, a simple benefit-cost analysis was adopted. Benefit was considered to
be the gain of statistical power in a two sample comparison. Cost was considered to be the
increase in resources required for each additional replicate, using a fixed cost per replicate.
Therefore, the objective of the preliminary sampling was to:
1. Determine the optimum number of replicates; 50
2. Determine the statistical power of the experiment;
3. Undertake cost benefit analysis; and to,
4. Finalize the experimental design of the study and appropriate statistical analysis.
3.2.2 Method
An initial experiment was performed to estimate the optimum number of replicates to be
used in the study of the seven south coast estuaries. Ten replicate hauls using a seine net
(6nim mesh size, 12m long, 2m high) were carried out during September 1997 in the
entrance channel of Lake Illawarra to provide the data for the benefit-cost analysis. All
fish caught were identified to species level and counted. Numbers of species and numbers
of individual fish captured per haul were recorded. These data was arranged to provide a
two sample comparison using Analysis of Variance (ANOVA) (n=20). Prior to analysis,
abundance data were ttansformed using logio(x + 1) to assist in stabilizing variances, as
recommended by Lester et al (1996) and widely used in similar fisheries studies (Gray et
al 1996). Power analysis was then used to calculate the least number of replicates which
provided a significant result {p=0.05) for changes between 10%) and 100%) in the mean
number of individuals and mean number of fish species. This has been termed the least
significant number (LSN) of replicates for each effect size. Since it was considered that
between two and six replicates at each site within an estuary was possible within existing
time and resource consttaints, these options were investigated in more detail in terms of
their power to detect a specified effect. 51
3.2.3 Results
Figure 3.1a shows the estimated least number of replicates required to determine a significant difference {p=0.05) between two samples when the mean of those samples differ by an "effect size" of between 10%o and 100%o. This relationship is shown for both numbers of individual fish and numbers of fish species. Numbers of individual fish in replicates is larger and fluctuates more than numbers of flsh species and is therefore the more important variable in examining the optimum number of replicates. For numbers of individuals, these data indicated that in a two sample test, three replicates allows an effect size of about 40% to be detected, and four replicates allows an effect size of about 30%) to be detected. Increasing the number of replicates above six provides little in additional power (Figure 3.1a).
Figure 3.1b uses only data on numbers of individual fish and demonsttates the increase in statistical power with increasing number of replicates, for specified effect sizes. Statistical power is the probability of detecting the specified effect and generally a power of greater than 0.7 is considered acceptable (Lester et al 1996). Using the pilot study data, only effect sizes of over 30% could be determined with acceptable power and this required more than three replicates. A benefit-cost analysis was carried out using data on numbers of individual fish and a fixed cost of sampling. This indicated that for effect sizes of between 25% and 35%o, the best ratio of statistical power to cost was obtained using four replicates (Figure 3.1c).
On the basis of these available data, four replicates at each site was considered to be the optimum sample size when using the seine net in the larger sampling program. 52
A, 100 80 -
60 - Number of individuals 40 _ Number of species 20 /
0 T 1 1 1 1 1 1 r— —I 1 0 2 4 6 8 10 12 14 16 18 20 Number of replicates
f^ 1.25 B. 1-001 ; ''""•'"•^"s. 0.75 1.00 ^ u 4wyy ^ 0.75 5 0.50 8 35%/\/' Pi i 0.50 . 30%w/j 25yj^ 0.25 s 0,25
0 1 1 1 1— 1 1 0 2 3 4 5 6 7 12 3 4 5 6 7 Number of Replicates Number of Replicates
Figure 3.1: Relationship between number of replicates and minimum detectable effect size (A), statistical power (B) and benefit-cost ratio (C). Figure 3,1 A shows data for numbers of individual fish and nimibers offish species whereas Figure 3, IB and 3.1C show data for numbers of individuals only.
3.3 Method
3.3.1 Site Location
The sttidy was conducted between WoHongong (34°33'S, 150°52'E) and Merimbula
(36°54'S, 149°55'E) on the soutiieast coast of New South Wales, AusttaHa (see Figure
1,1), Six large ICOLLs were sampled every quarter for three years. The estuaries sampled during this study were Lake Illawarra, St Georges Basin, Lake Conjola, Burrill Lake, Coila
Lake, and Wallaga Lake (Figure 3,2-3.8). After the first year Merimbula Lake was added 53 to the research to extend the geographic range of the study. The classification and size of these estuaries is shown in Table 3.1. Extensive recreational fishing and prawning occurs in each ofthese ICOLLs, and at the time of sampling commercial fishing was permitted in
Lake Illawarra, St Georges Basin, Burrill Lake, Lake Conjola, Coila Lake and Wallaga
Lake. No commercial fishing occurs in Merimbula Lake but an intensive oyster farming industry exists. The lakes have varying degrees of entrance opening and closing, ranging from mostly open (Merimbula Lake, St Georges Basin and Lake Illawarra) to intermittently open (Lake Conjola, Burrill Lake and Wallaga Lake), to the mostly closed
(Coila Lake).
Three shallow water locations within each esttiary were chosen. These sampling locations were: at the enttance channel of each lake; adjacent to the shore of the centtal basin of each lake; and adjacent to the westem or back shoreline of each lake. Throughout this thesis these locations will be referred to as the Enttance, Centtal and Upper locations.
Sampling sites were chosen haphazardly in seagrass beds at each of these locations within each estuary (Figures 3.2-3.8).
Table 3.1: Description of estuaries sampled in the three-year study offish commiuiities in shallow water seagrass habitats along the south-east coast of New South Wales, Data fi-om(Wes t et al. 1985; DLWC 2000)
Estuary Name Classification Catchment size Size of estuary Seagrass area (km^) (km^) (km^) Lake Illawarra Barrier lagoon 150.0 36,0 5,1 St Georges Basin Barrier lagoon 390,0 38,9 8,5 Lake Conjola Barrier lagoon 145.0 5,8 0,5 Burrill Lake Barrier lagoon 75.0 4,2 0,5 Coila Lake Coastal lagoon 48.0 9,0 1,9 Wallaga Lake Barrier lagoon 28.5 7,8 1,3 Merimbula Lake Barrier lagoon 48.0 4,6 2,3 54
3.3.2 Water quality
Physiochemical variables that were expected to influence the Httoral fish assemblage were measured concurrently with fish sampling. Water temperature (°C), conductivity (^is/cm) and salinity (parts per thousand) were measured at mid-depth, with an MC-84
Conductivity-Salinity-Temperature handheld meter, A handheld Whitman waterproof pH meter was used to determine pH, A water sample was taken at mid-depth to determine turbidity in nephelometric turbidity units (NTU), using a laboratory based Model 6035
Turbidimeter, Other environmental variables that were noted at each site included water depth, sediment type, seagrass species and the percentage cover of seagrass. Due to problems with equipment no samples for turbidity were taken during the October 1997 sampling event, and there are no pH values for the Febmary 1999 sampling event.
3.3.3 Fish Sampling
Sampling of the fish communities in the selected estuaries was carried out under the conditions of NSW Fisheries Scientific Permit (F96/294) and University of Wollongong
Animal Etiiics Permit (AE 96/18),
Sampling of the juvenile fish assemblages associated with the shallow water seagrass habitat (usually Zostera capricomi) in the six estuaries was conducted on twelve occasions from September 1997 to July 2000, Merimbula Lake was added to the sampling program in July 1998. Samples were collected using a seine net with a 25m headline, 2m drop and
6nim sfretched mesh. This net surrounded an area of approximately 25m^. Plate 1 shows the use of the seine net used in this research. Four replicate samples were collected from each location in the seven estuaries, resulting in 84 samples for each sampling event. All sampling was conducted at mid-tide and during daylight hours. 55
Plate 1: Deployment of the seine net (6nim stretch mesh, 25m long) used for sampling of shallow water seagrass fish communities in this study.
All post-larval fish identification and sorting was carried out in the field to reduce mortality of fish. Fish were identified to species level, a total number recorded and released back to the water. The fork length (FL) was measured to the nearest millimette
(mm) for fish species considered to be of commercial and/or recreational significance (see
Chapter 5), Individual fish requiring further identification or to be collected as a voucher specimen were humanely killed by placing in ice water and then preserved in 70% ethanol.
The reference collection was further identified to species by the Austtalian Museum
(Sydney, Austtalia), Identification of fish in the field was carried out using standard reference texts (Hutchins & Swamston 1986; Kuiter 1993),
3.3.4 Data Analysis
All data were entered into a specially designed database (Claris Filemaker Pro) at the end of each sampling period and manually cross-checked to eliminate errors. 56
Analysis of Variance (ANOVA) was used to test for significant differences in fish species diversity and number of individuals (abundance), between the factors of "location" and
"sampling event" within estuaries. The factor of Sampling Event was considered random.
Location was considered as a fixed factor as they were chosen to be representative of different regions within the ICOLL. The two-factor ANOVA was also performed on total number of commercial fish species and total abundance of commercial fish caught.
Abundance data displayed heterogeneity and were ttansformed using logio(x+l), prior to these analyses. In some cases this transformation did not produce homogeneous variances, but ANOVA was used regardless as it is considered quite robust to departures in homogeneity when sampling sizes are equal (Underwood 1981), To compensate for the
increased likelihood of Type 1 error, a was set to 0.01, Where ANOVA indicated
significant differences among means, the Student-Newman-Keuls test was used for post- hoc comparison of means.
To examine the effects of environmental variables, the number of fish species and abundance of individuals were correlated with salinity, water temperature, turbidity, pH and vegetation cover {% value). Multiple regression analyses were used to determine if there was a significant correlation between the environmental parameters and species diversity and abundance within each estuary, and which environmental variable best explained the variance observed for the overall number of species and individuals. 57
Upper 10 1 Kilometers
Figure 3,2: Entrance, Central and Upper sampling locations in Lake Illawarra, NSW. See Figure 1.1 for map of region. 58
N A
1__? ? kilometres
Figure 3.3: Entrance, Central and Upper sampling locations in St Georges Basin, NSW. See Figure 1.1 for map of region. 59
Figure 3.4: Entrance, Central and Upper sampling locations in Lake Conjola, NSW, See Figure 1.1 for map of region. 60
Figure 3.5: Entrance, Central and Upper sampling locations in Burrill Lake, NSW. See Figure 1.1 for map of region. 61
Figure 3.6: Entrance, Central and Upper sampling locations in Coila Lake, NSW. See Figure 1.1 for map of region. 62
0 e
A
kilometres
Figure 3.7: Entrance, Central and Upper sampling locations in Wallaga Lake, NSW, See Figure 1,1 for map of region. 63
Figure 3.8: Entrance, Central and Upper sampling locations in Merimbula Lake, NSW. See Figure 1,1 for map of region. 64
3.4 Results
3.4.1 Environmental Data
The seven estuaries exhibited similar ranges of temperature, with these minima and maxima temperatures related to seasonal effects (Figure 3.9). The minimum temperature of 8.7°C was found at Wallaga Lake and the maximum temperature of 34.0°C in Lake
Illawarra. This high value was recorded at the upper location of Lake Illawarra in shallow water (0.3m) during high air temperature.
Notably, there was no gradient in salinity with increasing distance from the estuary mouth
(Figure 3.10), Indeed, for some of estuaries such as Coila Lake, Wallaga Lake and
Merimbula Lake, the salinity values were nearly identical at the enfrance, cenfral and upper locations (Figure 3,10), and all lakes displayed a general lack of a progressive decline in salinity away from the enttance. The range of salinity values was similar for
Lake Illawarra, St Georges Basin, Burrill Lake and Wallaga Lake. These ICOLLs had minima in the range between of 20.0-25.Oppt to maximum salinities approximately equal to seawater (36.0ppt) (Figure 3.10). The salinity values for Coila Lake were within the same range for the first year of sampling, but salinity fell during the second year to between 6.2 to 16.6ppt (Figure 3.10). Coila Lake water then became increasingly saline in the third year of sampling, even after a substantial period of enttance closure. The range of salinity values in Lake Conjola ranged from 6.2 to 36.0ppt and this large range in salinity was related to a single freshwater event in October 1997 at the upper location
(Figure 3.10). pH values were quite consistent among the estuaries, with the majority of samples ranging from 7.4 - 9.1, witii no major difference in pH between the three locations (Figure 3.11). pH values outside tiiisrang e were found on two occasions. A value of 6.8 was recorded 65
Lake Illawarra 35- St Georges Basin
30- • 25- VA: •^ • 20- / •^: 15- * 10- A
S- 1 1 1 1— 1 1 1 10/97 2/88 4/98 7/98 10/98 2/99 4/90 7/99 10/00 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00
35-] Lake Conjola 35- Burrill Lake
30- /\ • A 25- -• 25- 1 ^•.. "•\ 20- • / ^ 20- :/•- \ ^^ /\ / 15- • t 16- "• ». 10- 10- v' V s •' i * 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 s. E 35- Coila Lake 35- Wallaga Lake
30- • A • 25. 25- -«x i ^^ A * i \ A -*. X 4/ u- . * 20. 20- \ • ••-:; A' V ••\ ', •. \ L 15. 15- / \ • H / 10. A 10- w
5. —r 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Events
35- Merimbula Lake - entrance central 30J upper
25. A A
20. /^^^^^V \ •*^\ y/ r 15. / « • \ / 10. # ^4
7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Events
Figure 3.9: Temperature (° C) values taken on each sampling event over the three-year period, at the Entrance, Central and Upper locations within each of the seven estuaries. Note Merimbula Lake sampled two years only. 66
• • \ • —• • t • ^\. A \ ft /»:-* • • / A « 1 •/• •
Lake Illawarra St Georges Basin
1 1 1 1 r 1 1 1 1 r 1 1— 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00
M —- • _ /^^ri' X ^./i 4 i I •: 30- 30. 8 a. • V X •' A'' • '' A • / \ /' s' ic ^* 20- A \/ 20.
Sa l • • A
Lake Conjola Burrifl Lake 10- / 10. A
0- 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00
1^ \-\ - ^ • /V ^*-. /A. - I • / \/ \ • \ .^.J / Coila Lake Wallaga Lake \/ 8
r 1 1 1 1 1 1 1 1 1 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Events
/ ^f^ t ^B'^ ^t- « "^* - entrance - central • upper
- Merimbula L2
10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Events
Figure 3.10; Salinity values (parts per thousand) at the Entrance, Central and Upper locations within each estuary over the three-year sampling period. Note Merimbula Lake sampled for two years only. 67
10 10 10 Lskelilauna UkeCtrjda
* it * =-•-* • * * * ir * * * •* *
6-
4-
2-
OH r n 1 1 1 1 1 1 1 1 1— 0-1—r 1QW2I98 498 7/981IM82f99 4S9 TmrmlKD 40) 7100 HWraBB 49B 7(961098298 49B 7/98109920) 400 7ffl0 1037298 498 7)981093298 499 7/9910992103 40D 7/CD
10-, 10 10 BiiriilUke CdlaLake V\iHlagaUke # * * * * * * * t * * t-t * * * ' * f -* *-* •-• i * # pH 6-
4-
2-
—1 1 1 1 1 1 1 1 1 1 1 1— I 1 I I I I I I I I I I I I I I I I I I I I I I 10S72/9B 498 7/961098298 4SB 7>981O9B0GO 400 TnO 1097398 49B THB1098298 499 7/981098200 400 7/00 109/298 49B 7798109B 298 498 7/981098 200 400 7/00 SanrplirigBats 10-, lU^ntiiaLate
-^-ertranoe
—I—I—I—I I I—I I I 1098 298 498 7/96 1098 200 4CD 7700 imping Berts
Figure 3.11: pH values at the Entrance, Central and Upper locations within the seven estuaries over the three year period. Note Merimbula Lake sampled for two years. 68
ENTRANCE CENTRAL UPPER
Lake Illawarra
^ n^n^^n ni^i, , , n^,m_r n^i 10/872/98 4/98 7/9610«82ra9 4/99 7/99 10/992/00 4/00 7/00 10/972/98 4/98 7/S6 10/98 2/99 4/99 o7/9910/992/0 0 4/00 7/00 10*7 2/98 4/98 7/98 10/98 2/99 4/99 7/9910/99 2/00 4/00 7/00
St Georges Basin
m_^„„RiF^nnr^ . n 10/972/98 4/98 7/9810/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/972/08 4/98 7/96 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/972/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00
Lake Conjota n
10/972/8ri^^^rnrri0 4/98 7/9910/982/99 4/99 7/9910/992/0n nn.0 4/00 n7/00 10/972/98 4/08 7/9810/982/99 4/98 7/8010/882/00 4/00 7/00 10/972/98 4/98 7/0810/882/98 4/88 7/9810/882/00 4/00 7/00
I-
3 nn^-. ^^n^nn. n - mn 10/872/98 4/98 7/9810/982/99 4/99 7/9910/992/00 4/00 7/00 10/972/98 4/88 7/9810/882/99 4/89 7/9910/992/00 4/00 7/00 10/972/98 4/98 7/9810/982/99 4/99 7/9910/992/00 4/00 7/00
Coila Lake
ra n[^^_, .^F^ da nn_.nnn n in nni u n 10(972198 4198 719810(982(99 4(99 7l9910f9fl2(&r0 4(0aD 7f00 10/972/98 4/98 7/9810/982/99 4/98 7/9910/992/00 4/00 7/00 10(972/98 4/98 7/9810/982/99 4/99 7/9910/892(00 4(00 7(00
Wallaga Lake
nn^nm^nm^F?]. n = iXL 10/972/98 4/98 7/9810/982/99 4/99 7/9910/992/00 4/00 7/00 10/972/98 4/96 7/9810/962/99 4/99 7/9910/992/00 4/00 7/00 10/972/98 4/98 7/9810/982/9ml 9 Hn4/99 7/9910/992/0i 0 4/00 7/00
Merimbula Lake
iH , n 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2/99 4/99 7/98 10/99 2/00 4/00 7/00 Sampling Events
Figure 3.12: Turbidity values (NTU) recorded at the Entrance, Central and Upper locations within each estuary over the three-year sampling period. Note Merimbula Lake sampled for two years only. 69 for Burrill Lake waters at the entrance and a value of 5.2 at the upper location of Lake
Illawarra, both during April 1999 (Figure 3.11). The upper location of Lake Illawarra had the highest recorded turbidity reading (59.5 NTU) in April 1999 (Figure 3.12). Turbidity values exhibited slight differences between the estuaries and also between locations. The lowest turbidity value recorded was 0.09 NTU for Burrill Lake at the entrance location in
July 1998, with the majority of locations within all the estuaries ranging between 0.1 to 10
NTU (Figure 3.12). Overall the highest turbidity readings were found at the upper
locations and this was particularly true for Lake Illawarra, where values generally
exceeded 30 NTU (Figure 3.12).
3.4.2 General Overview of Fish Communities
A total of 209 366 fish, belonging to 101 species and 48 families were caught in these
seven estuaries over the three-year study period (Table 3.2). Thirty-seven ofthese species
were considered to be of economic significance to commercial and/or recreational
fisheries. Composition of the seagrass fish fauna was dominated by non-commercial
species, and by juveniles of commercially important species (Table 3.2). On the basis of
categorising whether a species was marine, estuarine or freshwater species, it was
considered that approximately 69% were marine species, 25% estuarine species and 5 % of
all species represented freshwater species (based on Pollard 1994a; Kuiter 1993; Gray et
a/. 1996; West & King 1996). Overall, the families with the most species were the
Gobiidae (12 species), Monacanthidae (9 species) and Syngnathidae (8 species). Also well
represented in terms of species diversity were the Mullidae (4 species) and Scorpididae (4
species). In every lake, the Gobiidae, Monacanthidae and Syngnathidae families had the
highest number of species, but the number of species from each family differed among
estuaries. For example, in Lake Conjola 6 species from the Monacanthidae family 70
Table 3.2: Fish species captures and overall total abundance offish captured from the seven estuaries sampled from October 1997 to July 2000, Locations and sampling events have been pooled, * indicate species considered to be commercially and/or recreationally important.
FAMILY Dlawarra St Georges Lake Burrill CoUa Lake Wallaga Merimbula species Basin Conjola Lake Lake Lake Anguillidae Anguilla reinhardtii* - - 1 1 1 1 - Clupeidae Sardinops neopilchardus* - - 1 - - - - Hyperlophus vittatus* 1 3 1 1 - - 1 Spratelloides robustus ------9 Engraulididae Engraulis australis* - - - - - 5 - Gonorynchidae Gonorynchus greyi - - - - 1 - - Plotosidae Cnidoglanis macrocephalus - 2 - - - - - Antennariidae Antennarius striatus - - 1 - - - - Hemiramphidae Hyporhamphus regularis* - - - - 7 - - Hyporhamphus australis* 28 2 12 10 352 1 10 Belonidae Tylosurus gavialoides - 2 - - - - - Strongylura leiura - I - - - - - Atherinidae Atherinosoma microstoma 6084 29 1728 2493 29763 797 1436 Atherinosoma elongata 154 388 340 54 1998 40 92 Poeciliidae Gambusia holbrooki - - - - 169 - . Pseudomugilidae Pseudomugil signifer 3505 - 3318 42 1 3427 5 Fistulariidae Fistularia commersonii 1 - - 3 - - - Syngnathidae Hippocampus breviceps - 2 - - - - - Hippocampus whitei - 1 - - - - - Syngnathoides biaculeatus ------12 Vanacampus poecilolaemus 112 743 36 203 3 19 126 Urocampus carinirostris 191 73 125 173 315 771 100 Vanacampus phillipi 7 60 3 10 20 242 61 Stigmatopora nigra 46 216 56 45 - - 41 Stigmatopora argus - 277 - 52 - 9 163 Scorpaenidae Centropogon australis 102 23 118 21 4 83 31 Platycephalidae Platycephalus fiiscus * - - - - I - - Ambassidae Ambassis jacksoniensis 5746 9082 6478 14421 - 18081 1068 Terapontidae Pelates sexlineatus 429 1006 96 596 - 298 52 Apogonidae Apogon limenus ------1 Siphamia cephalotes ------79 Dinolestidae Dinolestes lewini* - . . _ . 1 - Sillaginidae Sillago flindersi * - - . - 8 - - Sillago ciliata* 1 - - _ 10 - - Sillago maculata* 4 - . . - - - Pomatomidae Pomatomus saltator* 157 135 369 28 - 211 10 71
Carangidae Psuedocaranx dentex* 1 - 1 1 - 3 69 Sparidae Acanthopagrus australis*' 537 36 481 43 811 667 17 Chrysophrys auratus* - 2 11 - - - 18 Rhabdosargus sarba * 27 5 9 1 - 44 10 Gerreidae Gerres subfasciatus* 468 - 197 12 - 150 76 Lethrinidae Lethrinus genivittatus - 1 4 - - - - Mullidae Upeneus species - - - - - 1 Upeneichthys species ------3 Upeneus tragula* 2 1 - - - - - Parupeneus signatus* 3 - - - - - 4 Monodactylidae Monodactylus argenteus* 31 22 16 22 - 30 - Girellidae Girella tricuspidata* 614 732 529 365 21 562 546 Scorpididae Scorpis lineolatus* 5 65 1 1 - - 5 Scorpis species* - - - 1 - - - Microcanthus strigatus - 6 - - - - - Microcanthus species - - - - - 1 - Enoplosidae Enoplosus armatus 19 7 2 3 - - 2 Pomacentridae A budefduf species - 1 - - - - - Mugilidae Mugil cephalus* 157 146 246 1551 3 520 32 Myxus elongatus* 90 260 880 126 4 136 84 Liza argentea* - - 363 4 427 134 - Sphyraenidae Sphyraenaflavicauda * 1 - 1 - - - - Sphyraena species* - - 1 - - - - Sphyraena obtusata - 5 - - - - - Labridae Achoerodus viridis* 115 21 58 8 35 6 78 Odacidae Odax acroptilus - 2 - - - - - Neodax balteatus ------34 Haletta semifasciata ------81 Scaridae Scarus species - - - 1 - - - Bovichtidae Pseudaphritis urvillii - 1 - - - 2 - Blenniidae Omobranchus anolius - 1 - - - 3 - Petroscirtes lupus 33 62 14 15 - 2 16 Clinidae Cristiceps argyropleura - - - - - 2 - Cristiceps australis - - - - 1 - 3 Heteroclinus perspicillatus ------6 Callionymidae Repomucenus calcaratus - - - - 2 - - Galaxiidae Galaxis maculatus - - 1 - - - - 72
Gobiidae-subfamily Eleotridinae Philypnodon grandiceps 1440 38 3445 342 572 167 30 Philypnodon species 1 - 44 2 11 2 - Hypseleotris compressa - - 8 1 - - - Gobiidae Bathygobius kreffti 5 5 4 - 2 4 10 Favonigobius lateralis 47 131 398 44 19 17 369 Favonigobius exquisites 47 2 161 7 1934 65 30 Amoya bifrenatus 256 1 54 13 23 120 21 Amoya frenatus 435 1 46 15 157 325 61 Afurcagobius tamarensis 1151 72 1156 95 256 742 67 Pseudogobius olorum 1093 18 311 450 131 1507 7 Redigobius macrostoma 73 90 1057 164 35 5758 40 Gobiopterus semivestitus 3349 301 13908 358 4609 25997 6 Siganidae Siganus nebulosus 2 20 6 10 - 11 20 Bothidae Pseudorhombus arsius* - - - - 1 - 2 Pseudorhombus jenynsii * - - - - 3 1 - Monacanthidae Scobinichthys granulatus* 4 12 - 6 - 15 10 Penicipelta vittiger* 1 2 - - - - 2 Acanthaluteres spilomelanums 7 132 10 6 - 22 96 Brachaluteres jacksonianus 2 1 - - - - 10 Monacanthus chinensis* 7 78 33 15 2 152 24 Meuschenia freycineti * 155 117 211 110 5 163 106 Meuschenia trachylepis* 205 339 288 144 1 156 9 Meuschenia species* - 42 23 7 - - 30 Nelusetta ayraudi 17 13 5 - - 4 5 Tetraodontidae Arothron flrmamentum 3 - - 3 - - - Tetractenos hamiltoni 20 2 1 3 3 1 39 Tetractenos glaber 8 7 1 14 11 2 46 Diodontidae Dicotylichthys punctulatus 37 5 3 37 - 13 8
Total Number of Fish 27037 14850 36672 22153 41732 61492 5430 Caught:
Number of Fish Species: 56 60 56 53 41 52 61
Number of Commercial Fish 24 20 23 21 17 20 20 Species:
Number of Unique Species: 0 9 4 2 7 2 9
Total Number of Fish: 209366
Total Number of Fish 101 Species:
All bream that were caught in this study have been classified as Acanthopagrus australis, even though Acanthopagrus butcheri (black bream) are found in the estuarine water of NSW, These two species are known to interbreed and hybrids of mixed external morphology are most common. Correct identification of the two species and their hybrids is not usually possible, and this is especially true for small juveniles. Thus, it is acknowledged that some of the Acanthopagrus australis caught in this study are quite likely to be A. butcheri. 73
(leatherjacket) were caught, whereas 9 species from this family were caught in St Georges
Basin and Lake Merimbula (Table 3,2).
During the first year of sampling, 95 888 fish were caught, while in the second year 71 239 individuals were caught. This change in abundance between years can be attributed to a decrease in numbers of the small, cryptic species in the second year. Many of these species occur in schools, and thus are often caught in high numbers. Species belonging to
Atherinidae, Pseudomugilidae, Ambassidae and Gobiidae displayed a 50% decrease in their abundance in the majority of the lakes in the second year of sampling. While the same number of commercial fish species was caught each year, there was an increase in numbers of individuals, from approximately 3000 in the first year, to 9000 fish caught during the second year. The most noticeable differences were for the species:
Acanthopagrus australis, Girella tricuspidata, Mugilidae species and Monacanthidae species. In the third year a massive decrease in overall abundance occurred, with the abundance of commercial fish species declining back to approximately 3500 individuals, and numbers of non-commercial fish declining to a total of about 37 000 fish. This decrease in numbers of fish caught was noticeable across all estuaries, but was most significant in Coila Lake and St Georges Basin, where there was an 80% and 75% decrease respectively in abundance from the first year samples to the third year. Lake
Illawarra, Lake Conjola and Burrill Lake experienced between 65-72% decrease and
Wallaga Lake had a 33% decrease in abundance of fish caught from the first to the last year of sampling.
Fish species of commercial and/or recreational importance were caught mainly at a size indicating recent settlement (< 40mm FL) (Worthington et al 1992). For example,
Pomatomus saltator and Acanthopagrus australis were caught at a range of small sizes, 74 with 93.4% and 78.24% of their catches less than 40mm in length. This was also true for estuarine-spawning species, such as Gerres subfasciatus where 84.4% of its catch was less than 40mm. Recruits were also found at a similar range of sizes around the estuary.
Catches of Acanthopagrus australis were of a size range 12-185mm at the enfrance, 11-
139mm at the cenfral location and 9-150mm at the upper location. Such size ranges were found for most commercial fish species, with fish as small as 10-12mm caught at all locations around the ICOLLs. Recruitment pattems of the major commercial species have been examined in detail in Chapter Five.
3.4.3 Overall Patterns in Mean Species Diversity and Abundance
There were no obvious pattems in mean species diversity and abundance. The cenfral
location of five of the seven estuaries (Lake Illawarra, Lake Conjola, Coila Lake, Wallaga
Lake and Merimbula Lake) had the overall highest mean species diversity (Figure 3.13).
For these estuaries, with the exclusion of Lake Illawarra, the mean species diversity was
lowest at the enfrance location (Figure 3.13). For Burrill Lake and St Georges Basin, the
mean diversity of species was highest at the enfrance location, but for St Georges Basin
there was little difference in the mean number of species caught at any of the locations
(Figure 3.13).
Spatial and temporal differences in overall mean abundances of fish varied greatly between ICOLLs. Mean abundance of individuals increased from the entrance to the
cenfral and then to the upper locations in Lake Illawarra and Wallaga Lake (Figure 3.14).
Although highest mean abundance occurred at the upper location for Burrill Lake, abundances of fish were quite even across all sites in this estuary (Figure 3.14). Mean abundances were quite similar at all locations within estiiary for Coila Lake, Merimbula
Lake and St Georges Basin. However, the enfrance location had a slightly higher mean 75 abundance in St Georges Basin and Coila Lake, and the cenfral location in Lake Conjola
(Figure 3.14). Merimbula Lake also had the highest mean abimdance at the central location, but overall there was comparably low mean abundance at all locations in this estuary (Figure 3.14, Table 3.2).
Lake Illawarra St Georges Basin
entrance central upper entrance central
Lake Conjola Burrill Lake
entrance_• cen tra_ I entrance central upper Coila Lake Wallaga Lake
entrance central upper kJLentrance central I Merimbula Lake Location
entranceL* central . upper
Location
Figure 3.13: Mean number of fish species caught at the entrance, central and upper locations within each estuary. Lines denote standard error. 76
-| Lake Illawarra ^ "1 SMt George Georges sBasi Ba n
entrance central upper nt ranee central upper
Lake ' T Burrill Lake
O) o
bentrance central upper entrance •_•central uppe_r c a ake ^ 1 Wallaga Lake I OX k^
entrance central upper entrance central upper a Location 1 Merimbul_ia Lake x lux
intrance central upper
Location
Figure 3.14: Mean log abundance offish caught at the entrance, central and upper locations within each estuary. Lines denote standard error.
3.4.3.1 The influence of environmental variables on diversity and abundance patterns
Multiple regression of the environmental variables (see Section 3.3.2) with species
diversity were all significant, but i^ values were generally low. Also significant variables
and how sfrongly they explained diversity pattems differed between estuaries (Table 3.3).
There was very weak significant correlation between species diversity and environmental
variables in St Georges Basin (r^ = 0.14, P<0.05), and Coila Lake {? = 0.15, i'<0.01), with
no single environmental variable correlating significantiy to number of species (Table 3.3).
The highest correlation was found for Lake Illawarra (r^ = 0.42, P<0.001), where salinity
and pH were positively correlated with species diversity, while vegetation cover was 77 negatively correlated (Table 3.3). The decrease in species diversity and abundance in Lake
Illawarra with increasing vegetation density may be a reflection of the reduced sampling efficiency of the seine net in dense vegetation. In the remaining estuaries, salinity and/or temperature were the main significant regressors and were positively correlated with species numbers (Table 3.3). However the r^ values were always quite low (0.21-0.36)
(Table 3.3), indicating caution when interpreting these results.
A similar situation occurred for the correlation between overall fish abundances and the environmental variables. Generally, revalues were again quite low (Table 3.3). This result could be related to an increase in species and individuals during the spring/siraimer months. St Georges Basin showed no significant correlation between abundance of fish and environmental variables (r^ = 0.10, P>0.05) (Table 3.3). For Coila Lake though, all the environmental variables showed a significant correlation with abundance pattems (r^ =
0.38, P<0.001). Temperature and vegetation cover were positively correlated with abimdance, whereas salinity, pH and turbidity were negatively correlated (Table 3.3). The negative correlation with salinity is probably related to the large numbers of hardyheads and gobies that were caught in Coila Lake when the enfrance was closed (see Table 3.2).
Notably, the degree of correlation between the environmental variables and species diversity and abundance pattems is confounded by the low range in the values of the environmental variables experienced at all locations throughout the ICOLLs. For example, salinity values only fluctuated 10-15 ppt over the entire sampling period and pH values generally by only 3 units. This small range in values means that these parameters may not be usefiil in explaining any observed pattem inspecies diversity and abundance pattems.
Hence, the low r^ values obtained from the multiple regression analysis revealed that the 78
environmental data collected throughout this study explained little in terms of variation in numbers of species and overall numbers of individuals.
Table 3.3: Results of multiple regression analysis offish species richness and abundance against environmental variables. For abundance, log transformed values were used. The sign in brackets indicates the direction of the relationship, *i'<0.05, **P<0.001, ***P<0,001. na indicates no variables significanr.
Estuary Species number Abimdance Statistical data Significant Statistical data Significant variables variables Lake Illawarra i"5,7g= 11.33 Salinity (+) *** ^5,78=10,09 Temperature r^= 0,42*** pH(+)* r^= 0,39*** Veg. Cover (-) * pH (+) * Veg, Cover (-) *
St Georges Basin F5M= 2.85 na ^5,86=1.82 na ^^=0.14* r2=0,10
Lake Conjola ^5,98= 6.64 Salinity (+)*** ^5.98= 4,77 Veg, Cover (+)** r^= 0.25*** Temperature (+)* r^= 0,20***
Burrill Lake ^5,98= 5,35 Salinity (-) ** ^5,98=4,05 Salinity (-) *** r^=0,21*** pH (+) * ^=0.17 ** Temperature (+)**
Coila Lake -^5,102= 3.55 na ^5.102= 12.35 Temperature ^=0,15** r^=0.3S*** Salinity (-)*** pH(-)* Turbidity (-) * Veg, Cover (+)***
Wallaga Lake •f5,102= 6.43 Salinity (+) *** •^5,102-3.83 Salinity (+)^ r^= 0,24*** ^^=0,16**
Merimbula Lake ^-5,42= 4.75 Temperature (+)* i^5,42= 5.60 Temperature (+)* r^= 0.36** ^= 0,40*** Salinity (+)*
3.4.4 Spatial and temporal variability in flsh species diversity and abundance within
ICOLLs
In this section spatial and temporal variability of species diversity and abundance within
each ICOLL will be examined separately. 79
3.4.4.1 Lake Illawarra
A total of 27 044 fish were caught in Lake Illawarra over the three year sampling period.
Fifly-five fish species were found, of which twenty-three species were considered of significance to commercial and/or recreational fisheries (Table 3.2). In terms of individual numbers, the families Gobiidae (7897 individuals), Atherinidae (6246), Ambassidae (5746 individuals), and Psuedomugilidae (3505) dominated the seagrass assemblage and constituted approximately 87% of the total catch. Numbers within these taxa varied greatly between each location within the estuary, with some species showing restrictions in their distribution. For example, Pseudomugil signifer was caught only at the upper location, while Favonigobius lateralis had preference for the entrance site. Atherinosoma microstoma, Amoya frenatus, Afurcagobius tamarensis, Pseudogobius olorum and
Gobiopterus semivestitus were consistently found in higher abundance at the upper location throughout the sampling period. Notably, large numbers of these schooling species was the main reason that, overall, the highest number of individuals were caught at the upper site (14 548 individuals), whereas only about half that number of overall individuals were caught at either the enfrance or cenfral locations (Table 3.2). Seven species were caught on only one occasion and these included Hyperlophus vittatus,
Pseudocaranx dentex and Sphyraena flavicauda. There were no species that were unique to Lake Illawarra (Table 3.2).
Also, dominant among the finfish catches from Lake Illawarra were a number of economically important species such as, Girella tricuspidata, Gerres subfasciatus,
Acanthopagrus australis, Meuschenia trachylepis and Mugil cephalus. These commercial species were found at all of the sites, hxii Acanthopagrus australis and Gerres subfasciatus were caught in higher abundance at the upper site, whereas Girella tricuspidata and 80
Meuschenia trachylepis were found more frequently at the entrance and central location
(Table 3.2).
The mean number of fish species differed significantly between locations and sampling events within Lake Illawarra, and there were significant two-way interactions in these factors (Table 3.4). Differences in mean species richness was highly dependent on sampling event (p < 0.001). There was no consistent seasonal frend to these differences in species richness between years (Figure 3.15). High species diversity was found at the entrance during October 1997 and 1998, probably due to the influx of new recmits, including species such as Girella tricuspidata, Achoerodus viridis, Acanthopagrus australis, Scorpis lineolatus, and four Monacanthidae species. However in 1999, during the same seasonal period, exfremely low species diversity was recorded at the entrance location, and this was lower than the poor diversity caught during the winter sampling period of 1998. The central location also exhibited the highest diversity of species during
Febmary 1999 and April 2000 (Figure 3.15).
The mean numbers of individuals found in Lake Illawarra also differed significantly among locations and sampling events, and there were also significant interactions between these factors {p < 0.001, Table 3.5). Lowest mean numbers were caught at enfrance locations during April and October 1999, and July 2000, and either one or all ofthese samples were significantly lower compared to the rest of the catches. Overall highest mean numbers of fish were most commonly caught at the upper location within Lake
Illawarra, and this was particularly so during the first year in the months of October,
Febmary and April (Figure 3.15). At the upper site during July 1999, a high catch was the result of large numbers of three species, namely Gobiopterus semivestitus, Afurcagobius tamarensis and Pomatomus saltator. 81
Table 3.4: Summary of analyses of variance for mean numbers of species for each individual estuary Mean square values are shown. L, Location within estuary; SE, Sampling Event; d,f, degrees of fi-eedom, *P < 0.01, **P< 0,001,
Source d,f Lake St Lake Burrill Coila WaUaga Merimbula Illawarra Georges Conjola Lake Lake Lake Lake Basin
Location 15.0 6.76 198,4* 43,75 12,6 164,8** 29,39 (df 2) (L) Sampling Event 11 63.48** 30,54** 54,6* 28,49** 27,72** 119,04** 99,19** (SE) (df7)
LxSE 22 27.34** 13,5** 19,1* 14,81** 9,27** 17,08** 22.74** (df 14)
Table 3.5: Sxmmiary of analyses of variance for mean numbers of individuals for each individual estuary Data transformed using log(x +1). Mean square values are shown. L, Location within estuary; SE, Sampling Event; d.f, degrees of fi-eedom. *P < 0,01, **P < 0,001,
Soiu-ce d,f Lake St Lake Burrill Coila Wallaga Merimbula Illawarra Georges Conjola Lake Lake Lake Lake Basin
Location 2 3.74 0.46 10.9* 0,20 0.53 3,93* 0,22 (df 2) (L) Sampling Event 11 1.90** 0,96** 0,92* 2,02** 2,37** 2,66** 1,82** (SE) (df7) LxSE 22 0,55** 0.68** 0,47* 0,74** 0.96** 0,45** 0,24 (df 14)
Differences in diversity of commercial species of fishes in Lake Illawarra were more dependent on time of sampling (Table 3.6), but diversity was quite even amongst the three locations. Surprisingly, there were no differences in the numbers of fish of commercial significance or in the number of commercial fish species between the enfrance, middle and upper locations of Lake Illawarra (Table 3.6, Table 3.7). However, these differences were not consistent between sampling events and there were significant two-way interactions for 82
{fii Abundance of Fsh (B)DivefsayafFish 16-1
14-
3 - .12-
I_10 - ? ,c w I I 16. S 1 4-1
2
—I 1 1 1 1 1 1 1 1 1 1 1— 0. 1 1 1 1 1 1 1 1 1 1 1 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 (Q Abundance of Commercial Feb (D) Diversily of Comnercial Fsh lOOn 10-,
1 1 1 1 1 1 1 1 1 1 1 1 T r 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00
San^ng Events
Figure 3.15: (A) Mean abundance (log x+1) offish, (B) Mean number offish species, (C) Mean abundance of commercial fish and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Lake Illawarra over the three year sampling period. Lines denote standard error. 83 both abundance and diversity ofthese species (Table 3.6, Table 3.7). There was a large increase in the diversity and abundance of commercial species during the second year of sampling, which was most noticeable at the enfrance and cenfral locations (Figure 3.15c &
3.15d). Species that were not caught during the spring/summer recruitment period in the first year but recruited into Lake Illawarra during the second year included, Enoplosus armatus, Scorpis lineolatus and Nelusetta ayraudi. The increase in recruitment during the second year was most noticeable in terms of abundance. At the entrance location there were major increases in the numbers of Achoerodus viridis and Acanthopagrus australis, but there were also general increases in the numbers of most commercial species, for example Girella tricuspidata and Meuschenia freycineti. However, the highest mean abundance of commercial fish was caught at the central location during October 1998
(Figure 3.15), where the catch was dominated by Girella tricuspidata, Meuschenia trachylepis, Meuschenia freycineti and Acanthopagrus australis.
Table 3.6: Summary of analyses of variance for mean numbers of commercial and/or recreational fish species for each individual estuary. Mean square values are shown. L, Location within estuary; SE, Sampling Event; d.f, degrees of freedom, *P < 0,01, **P < 0,001,
Source d.f Lake St Lake Burrill Coila Wallaga Merimbula Illawarra Georges Conjola Lake Lake Lake Lake Basin
Location 2 7.20 12.47** 31,42** 6,63 0,51 48,03** 0,073 (df 2) (L) Sampling Event 11 18.92** 5,06* 21,98** 4,30 8,85** 30,57** 12,87** (SE) (df7)
LxSE 22 9,17** 3,51* 4.80* 4,82** 2 9j** 5,87 9,17* (df 14) 84
Table 3.7: Summary of analyses of variance for mean abundance of commercial and/or recreational fish species for each individual estuary. Mean square values are shown, L, Location within estuary; SE, Sampling Event; d.f, degrees of fi-eedom. *P < 0,01, **P < 0,001,
Source d,f Lake St Lake Burrill Coila Wallaga Merimbula Illawarra Georges Conjola Lake Lake Lake Lake Basin
Location 2 352,3 3403,7 24325,8** 12869** 702,8 1199,2 4883,2 (df 2) (L) Sampling Event 11 3775,4** 2615.1* 4906,96** 14424.7 2858 2524,2** 610.25 (SE) (df7)
LxSE 22 683,1* 3015,4** 3293,23** 11581,4** 2077,6 1749** 254,5 (df 14)
3.4.4.2 St Georges Basin
Over the three-year study period 14875 fish were caught in St Georges Basin, representing
60 species. Twenty species were considered important to commercial and recreational fisheries (Table 3.2). Of the estuaries sampled, St Georges Basin had the most diverse seagrass fish community but the second lowest abundance of fish. In terms of abundance of individual species, the catch was dominated by Ambassis jacksoniensis (9082 individuals), Pelates sexlineatus (1006 individuals) and Vanacampus poecilolaemus (743 individuals). These species were caught in differing abundance throughout the lake.
Ambassis jacksoniensis were caught in high abundance at all the locations, while
Vanacampus poecilolaemus were found primarily at the enfrance and upper locations in higher numbers. In the commercial finfish category, Girella tricuspidata, Meuschenia trachylepis, Myxus elongatus, Mugil cephalus and Pomatomus saltator were dominant species in this lake (Table 3.2).
Ten species were caught only on one occasion and these included the seahorse species.
Hippocampus whitei, Upeneus tragula and Omobranchus anolius. Nine fish species were unique to the St Georges Basin catches, including Cnidoglanis macrocephalus, two 85
Species of longtom (Belonidae) and two species of seahorse {Hippocampus breviceps and
Hippocampus whitei) (Table 3.2).
The mean number of fish species and individuals differed significantly between location and sampling events (significant two-way interaction Table 3.4, Table 3.5), but differences were again highly dependent on timing of the sampling event (p<0.001). With species diversity, means-comparison tests revealed significant differences between the low mean number of species caught during July 1999 and 2000 at the cenfral location, compared to the higher diversities found during October 1999 and February 2000 at the cenfral and upper locations respectively (Figure 3.16). These high species diversity was due to large number of goby species (Gobiidae), as well as commercial species such as leather) ackets
(Monacanthidae), mullets (Mugilidae), Pomatomus saltator and Monodactylus argenteus.
Two species were only found in St Georges Basin, namely Strongylura leiura and an
Abudefduf spp. (Table 3.2). Highest mean abundance of fish occurred at the cenfral location during April 1998 (Figure 3.16). There was also relatively high species diversity at this time (Figure 3.16). The high mean abundance was largely a result of a substantial catch of Ambassis jacksoniensis. High mean abundance was also found during July 1998 at the upper location and at the enfrance during Febmary 1999 (Figure 3.16). The lowest mean abundance occurred during February 1999 at the central location and at the enfrance in July 1999, and these events were significantly lower to the six highest mean abundance events (Figure 3.16).
Differences in the ntmiber of commercial species were not consistent across localities within St Georges Basin or between sampling times (pxO.Ol, Table 3.6). Overall, the number of commercial species declined with distance from the estuary mouth but differences also occurred due to time of sampling. Highest mean diversity of commercial 86
(A) Abundance of Fish (^Diversity of Rsh 15-1 - entrance central upper 12 - • f I ./*X ^ I 9 i 2. +-^- + \\ /^ -Tx \^T T \ ..r CO • # c A • 3 6- E i'"' c r^ ^1-.-^ c A'' 1- T ^'^''^ T
1 1 1 1 1 —I 1 1 1 1 1— —1 1 1— —1 1 1— 10(97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 1099 2/DO 4/00 7/00 1(V97 2S8 4/98 7/98 1096 2/99 4/99 7/99 1099 2/DO 4/00 7/00
(C) Abundance of Comnercial Fish (D) Diversity Of Comnercial Fish 233-, 10-
180
160
140
120
100
80 •S 4- U d 60
40
20-
0 A M-T-K —r- —1 1 1 1 1QS7 2/96 *9e 7/96 10/96 2/99 4/99 7/99 1099 2/QO 4/00 7/00 1097 Zrae 4«8 7/98 1096 2/99 4^9 7/99 1099 20) 4/00 7/DO
Sampling Events
Figure 3.16: (A) Mean abundance (log x+1) offish, (B) Mean diversity offish species, (C) Mean abundance of commercial fish and the (D) Mean diversity of commercial fish species, caught at the entrance, central and upper locations of St Georges Basin over the three year sampling period. Lines denote standard error. 87 species occurred at the entrance location during February and during April 2000 (Figure
3.16), when species such as Pomatomus saltator, Achoerodus viridis, Acanthopagrus australis and six Monacanthidae species were caught (see Table 3.2). No commercial
species were found at the upper location during February 2000, and the lowest commercial
fish diversity occurred at this location during July 1998 and October 1997 (Figure 3.16).
Mean abundance of commercial species did not differ significantly between localities, but
differences existed between sampling times, and the interaction term was significant
(Table 3.7). This was because a significantiy higher mean abundance were caught at the
cenfral location during October 1998 and at the entrance during October 1997 compared to
all other sampling events. The high catch of commercial fish at the cenfral location was
dominated by Girella tricuspidata and Mugjl cephalus, whereas high numbers of Myxus
elongatus and Meuschenia trachylepis were caught at the enfrance in October 1997 (Figure
3.16).
3.4.4.3 Lalce Conjola
A total of 36 972 fish were caught in Lake Conjola, representing 56 fish species of which
23 species are considered to be of significance to commercial and recreational fisheries.
The overall catch was dominated by Gobiopterus semivestitus (14 974 individuals),
Ambassis jacksoniensis (6224), Atherinosoma microstoma (3110) and Philypnodon grandiceps (2462). The finfish catches from Lake Conjola comprised of species from the
Mugilidae family, with high numbers of Myxus elongatus, Liza argentea and Mugil
cephalus, and catches of Acanthopagrus australis, Girella tricuspidata and Meuschenia
trachylepis (Table 3.2).
Eight species were found on only one occasion, and these included commercial fish species, such as Sardinops neopilchardus, Hyperlophus vittatus and Scorpis lineolatus. There were four species that were tmique to Lake Conjola, namely Antennarius striatus,
Galaxis maculatus, Sardinops neopilchardus and a Sphyraenidae species.
There were significant differences in mean numbers of species and mean overall abundances between factors "location" and "sampling event" for Lake Conjola, as well as significant interaction between these factors (Table 3.4, Table 3.5). The majority of samples displayed significantly higher diversity when compared to the very low species diversity found at the entrance location during July 1998 (Figure 3.17), after the lake had been artificially opened. The enfrance location had similarly low species diversity during
April and July 2000 (Figure 3.17). The highest species diversity was frequently found at the cenfral location, particularly during the spring (October) and autumn (April) (Figure
3.17).
The situation was similar for mean overall abundance of fishes in Lake Conjola, where the enfrance samples of July 1998, 1999, 2000, and April 2000 were significantly lower than at the central and upper locations for the same period (Figure 3.17). At the cenfral locations this was largely a result of high catches of Gobiidae species and Monacanthidae species. At the upper location Gobiopterus semivestitus, Gerres subfasciatus and
Pseudomugil signifer were abundant.
Ntraibers of commercial fish differed significantly among locations and sampling events, and the interaction term was also significant (p<0.01. Table 3.7). There was a similar resuh for number of commercial fish species (p<0.001. Table 3.6). For Lake Conjola, the highest mean abundance of commercial fish and species diversity was more often found at the cenfral location within the lake (Figure 3.17). This was particularly tine for the
October 1998 sampling event, when high numbers of Acanthopagrus australis were caught, and tiie February 1999 sampling event when Myxus elongatus, Meuschenia 89
(A) Abundance of fish P Diversily of fish entrance 4-1 16 • centrai A upper 14 • I 3- 12 • • I I A « • • i • I1 0 • ^ 1 f • I • ^ • A - A I • •S 8 A A 3 I 6-1 C c A • 1- c » 4-
I I I I I I I I I I I I I —I 1 1 1 1 1 1 1 1 1 1 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2«)Q 4/00 7/00 (Q Abmdance of conrmercial fish (D) avetsXy of commercial fisii 10
8-
B 4 4 m A
A • A ' i / —I 1 1 T 1 1 1 1 1 1 1 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00
Sanding Everts
Figure 3.17: (A) Mean abundance (log x+1) offish, (B) Mean mmiber offish species, (C) Mean abundance of conmiercial fish and (D) Mean nimiber of commercial fish species, caught at the entrance, central and upper locations of Lake Conjola over the three year sampling period. Lines denote standard error. 90 trachylepis and Meuschenia freycineti were abundant at this location. The enfrance location experienced low catches of commercial fish during April 1999 and 2000, and July
1999 and 2000 (Figure 3.17). During July 1998, a decrease in the abundance and diversity of commercial fish species was quite evident in Lake Conjola, with no commercial species were caught at the entrance or upper locations, while low diversity and numbers were caught at the cenfral location (Figure 3.17).
3.4.4.4 Burrill Lake
22 214 fish were caught in Burrill Lake, representing fifty-three fish species of which twenty-one were considered of importance to commercial and recreational fisheries (Table
3.2). In terms of overall abundance, the catch was dominated hy Ambassis jacksoniensis
(14421 individuals) and Atherinosoma microstoma (2548), and Mugil cephalus (1551), which constituted nearly 84% of the total catch. Large schools of Ambassis jacksoniensis and Mugil cephalus were caught at the enfrance location and this meant that overall, nearly
50% of fish were caught from this location. The Burrill Lake commercial finfish catches were dominated by high numbers of Mugil cephalus, Girella tricuspidata, Meuschenia trachylepis, Myxus elongatus and Meuschenia freycineti
Eight species were caught only once from Burrill Lake. These included two species from the Scorpididae family and Pseudocaranx dentex. Two species were unique to Burrill
Lake, and these were an unidentified Scorpis species and Scarus species (Table 3.2).
Differences in the mean nimibers of species were not consistent across localities within
Burrill Lake or between sampling events, and there was a significant interaction between tiiese factors {p< 0.001, Table 3.4). Burrill Lake was similar to Lake Conjola, in that the 91 lowest species diversity was more often found at the enfrance location, and high diversity at the cenfral location (Figure 3.18)
Mean overall abundances did not differ significantly between localities, but did differ between sampling events (p< 0.001, Table 3.5). There was no consistent pattem between mean abundance and sampling event, however, peaks in abundance could usually be
attributed to a high catch of one or two species dominating the assemblage. For example,
high mean abundance at the upper location in October 1997 was due to high numbers of
Atherinosoma microstoma. High catch numbers at the enfrance location during July 1998
were due to Ambassis jacksoniensis, and high mean abundance at the cenfral location in
April 2000 was due to large numbers of Pelates sexlineatus and Ambassis jacksoniensis
(Figure 3.18). Very low numbers of individuals were caught at the entrance and cenfral
locations in July 1999, and at the entrance during October 1999 and July 2000 (Figure
3.18). Overall very low mean abundance of commercial fish species was found in Burrill
Lake, with the exception of a substantial catch of Mugil cephalus at the enfrance location
in October 1998 (Figure 3.18). The mean abundance of commercial species in Burrill Lake
differed significantly among locations and sampling events (significant two-way
interaction, p<0.001, Table 3.7) but differences depended on location (Table 3.7). The
range of diversity was quite similar across the three locations and it was common for
similar numbers of commercial species to be caught at two of the three locations (Figure
3.18). In February 1999, species such as Meuschenia trachylepis, Meuschenia freycineti
and Girella tricuspidata were found across all locations, while Mugil cephalus and Myxus
elongatus were included in the catch of the enfrance and cenfral, while Hyporhamphus
australis was caught at the cenfral and upper location. The mean number of commercial
species in Burrill Lake did not differ significantly among locations and sampling events, but the interaction between these factors was significant {p<0.00l. Table 3.6). 92
(A)AtXJndanceoffish (B) Diversity Of fish 4- 15 -•—entrance • central A upper 12 3- X+ 1 A 9-
(lo g • I A A • A •:". • A rt A I • • • • *'•: A •, I 6. A Abundanc e • • « A A
Mea n • 3- • 1 1
1 1 1 1 1 1 1 1 1 1 1 1— —I 1 1 1 1 1 1 1 1 1 1 1— 1QS7 2«8 4/98 7/98 10«8 2/99 4«9 7/99 10^9 2rtX) 4«0 7/00 10/97 2«8 4/98 7/98 10/98 2^9 4/99 7/99 10/99 2rt)0 4/00 7/00 (C) Abundance Of commercial fish (D) Diversily of commercial fish /UU-] 10
•i 600- «= la l i. i 500- E e o a 6. i400- o 9 a» 11 E o E c o 5 300- / \ u c •S 4-1 3 a(Q g 200- // \\ a> / \ S / \ 2- 100- / \ •:• A Ji
Q •-^i_=.—^ '' l^^i- 4 _-ll ' 1^ • T T T T 1 ^T T T T^ T T 1 1 1 1 1 1 1 1 1 1 1 1 1— 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10«9 2/0O 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10«9 2/00 4/00 7/00
Sampling Berts
Figure 3.18: (A) Mean abundance of fish, (B) Mean number of fish species, (C) Mean abundance of commercial fish and (D) Mean nimiber of commercial fish species, caught at the entrance, central and upper locations of Burrill Lake over the three year sampling period. Lines denote standard error. 93
3.4.4.5 Coila Lake
Coila Lake was consistently different to the other six estuaries, as only seventeen commercial fish species were captured over the entire three-year sampling period. In total, forty-one fish species were found, and the abundance of fish was quite high (41 785 individuals, see Table 3.2). This was due to the total catches being completely dominated by Atherinosoma microstoma and Atherinosoma elongata (31 814 individuals) and
Gobiopterus semivestitus (4609 individuals), which together constituted 87%) of the catch.
The dominant commercial fish species caught were Acanthopagrus australis, Liza argentea and Hyporhamphus australis.
Coila Lake was also the only lake in which an infroduced species was captured, namely
Gambusia holbrooki. Breeding populations of Gambusia holbrooki occur in both natural and altered environments, and heavily polluted habitats (Arthington & Mitchell 1986).
The perimeter of the lake has been classified as having moderate to high disturbance, mainly as a result of urbanisation around its enfrance and agricultural land dominating the land use around the rest of the lake (Bell & Edwards 1980).
Coila Lake seagrass fish catches included seven species caught only once, and these included species such Gonorynchus greyi and Cristiceps australis. Seven fish species were unique to Coila Lake, but most were common to sand habitat. These include
Platycephalus fuscus, Pseudorhombus jenynsii and Sillago flindersi
During the first year of sampling, Coila Lake was found to have an impoverished fish community (15 species) compared to the other locations (34 to 40 species), with only one species of economic importance, tiie garfish Hyporhamphus australis, being caught. Coila
Lake is a coastal lagoon witii low freshwater flows, resulting in a low frequency of 94 enfrance opening and short periods of ocean flushing. Under natural conditions, the entrance would probably remain closed for lengthy periods but is often mechanically opened to relieve flooding. The enfrance to Coila Lake had been closed for four years prior to this study, and remained closed for the first four sampling events of this study.
The entrance was mechanically opened in July 1998 and during the second year of
sampling, ocean-spawning species were present in the fish catches.
There was a significant spatial and temporal difference in species diversity within Coila
Lake {p <0.001, Table 3.4). The mean square values were far higher for time of sampling
than for location, which in tum was higher than the interaction term (Table 3.4). The
til enfrance was artificially opened on the 19 August 1998, and remained open for only two
and a half weeks. A consequence of this opening was an increase in species diversity at
the cenfral location (Figure 3.19) where such species as Achoerodus viridis,
Hyporhamphus australis, Meuschenia freycineti, Meuschenia trachylepis and
Acanthopagrus australis were infroduced into the system. High diversity also occurred at
the upper location in February 1999 where Acanthopagrus australis and Hyporhamphus
australis were caught, as well as Gobiidae species and three Syngnathidae species. The
enfrance was artificially opened again on 16''^ November 1999 and remained open for a
duration of six and a half weeks. Ocean spawning species such as Mugilidae species,
Acanthopagrus australis, Monacanthidae species, Sillago flindersi and Hyporhamphus
australis were caught during February 2000 resulting in relatively high mean diversity at
the cenfral and upper locations (Figure 3.19).
There were no significant differences in mean overall abundances between the three
locations witiiin Coila Lake, but there were significant variations between abundance 95
(A)Abmdaroeoffish (^Oversilyoffish
4-1 10' entrance central • • Lfjper 8- ^ 3- A__
t f §• * g 6. t 2- A A A c 3 XI A « i y/ \ c f
~1 1 1 1 1 1 1 1 1 1 1 1 1 —1—I—I—I—I—I—I—I—I—I—I—I— 10/S7 2/98 4/96 7/981098 2/99 Am 7/991099 2/DO AfXi IIQO 1097 208 4«8 7/981098 2/99 4/99 7/9910992/00 4/00 7/0O (C) AbundEvioe of ocxnmercial fish m Pversily of caiiTBtaal fish 240 10-
•5 6-
B 4-
o Sc 2 i,M •..«/? 0- « « --« «^ i •
—I—I—I—I—I—I—I—I—I—I—I—I— 10/972/98 4/98 7/981098 2«9 4/99 7/991CV99 2«) 4/DO 7/03 1097 208 4/98 7/981098 209 4/99 7/99 1099 2^0 4/QO 7/00 SampbTg Berts
Figure 3.19: (A) Mean abundance (log x+1) of fish, (B) Mean number of fish species, (C) Mean abundance of commercial fish and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Coila Lake over the three year sampling Pf^od. Lines denote standard error. , 96 throughout the sampling period (P<0,001, Table 3.5), and a significant interaction between
factors (Table 3.5). The sampling events where high mean abundance was foimd, such as
the enfrance February 1998 and April 1999, and the upper location in February 1999
(Figure 3.19), were a direct result of substantial catches of Atherinosoma microstoma,
Atherinosoma elongata and Gobiopterus semivestitus.
In terms of the abundance of commercial fish species, there were no significant
fluctuations among localities and sampling times, displaying a consistent infra-estuary
pattem (Table 3.7, Figure 3.19). A peak in abundance in February 2000 was directiy
attributed to a large haul of Liza argentea. There were significant interactions between
location and sampling event for mean diversity of commercial species within Coila Lake,
but the differences were sfrongly related to time of sampling, not location (Table 3.6).
This is largely related to the infroduction of the commercial species mentioned prior during
the period between July and October 1998.
3.4.4.6 Wallaga Lake
A total of 61 498 fish were caught in Wallaga Lake over a three-year period. Fifty-two
fish species were caught, and twenty of these species significant to commercial and
recreational fisheries (Table 3.2). In terms of abundance, Gobiopterus semivestitus (25
997 individuals), Ambassis jacksoniensis (18 081), Redigobius macrostoma (5758) and
Pseudomugil signifer (3427) were dominant. These small cryptic species were commonly
caught in large numbers at the cenfral and upper locations. Among the commercial fish
species found in Wallaga Lake, Acanthopagrus australis, Girella tricuspidata, Mugil
cephalus, Meuschenia freycineti and Meuschenia trachylepis comprised the majority of the
catch (Table 3.2). 97
Six fish species were caught only once, and these included Tetractenos hamiltoni and
Achoerodus viridis. Two species were unique to Wallaga Lake; Dinolestes lewini and
Cristiceps argyropleura.
The number of species and abundance of individuals differed significantly among
locations and sampling events, and the interactions between these main effects were also
significant (P<0.001, Table 3.4 Table 3.5). Differences in species diversity were more
strongly related to location effects (Table 3.4), with greatest diversity of fish species
usually found at the central and upper locations (Figure 3.20). This was particularly
evident during Febmary and April 1998, at the upper location and during Febmary and
October 1999 at the central location (Figure 3.20). The high diversity was largely a result
of the many Gobiidae species captured, four Syngnathidae species, as well as commercial
species such as: Pomatomus saltator, three Mullidae species, three Monacanthidae species
and Engraulis australis (see Table 3.2). A decrease in species diversity was evident in the
last year of sampling, most notably at the entrance location (Figure 3.20).
As with species diversity, the highest mean overall abundance was frequently found at the
central and upper locations (Figure 3.20). The mean square values were higher for time of
sampling, largely due to the peaks in abundance at the cenfral and upper sites during April,
July and October 1998 and April and October 1999, compared to the very low abundance
caught at the entrance during Febmary 2000 and at all locations in July 2000 (Figure 3.20).
High abundance could be attributed to large catches of Ambassis jacksoniensis, goby species such as Gobiopterus semivestitus, Pseudogobius olorum and Redigobius macrostoma, as well as moderate catches of Acanthopagrus australis. Mean abundance of commercial fish species did not differ significantiy between locations within Wallaga
Lake, but significant differences occurred between sampUng events and the interaction 98
(^Abundance offish (B)Diversiyaffish 2D-, entrance midclle upper 8" 3- I 15. eg c I 2 S 10. I E c 3 C C
I I I I I I I I I I I 1 —1 1 1 1 1 1 1 1 1 r--T 1 1 10/97 2/98 4/98 7/98 1098 2/99 4/99 7/99 1099 2/00 4/00 7AX) 1097 2/98 4/98 7/981098 2/99 4/99 7/991099 200 4/00 7/00 (Q Abmdance of comnercial fish ([^ Diversay of conrmdal fish 200-1 14-1
-1 1 1 1 1 1 r 1 1 1 1 1 1 1 1 r 1097 2/98 4/98 7/98 1098 2/99 4/99 7/991099 2/00 4/00 7/00 1097 2/98 4/98 7/98 1098 2/99 4/99 7/99 1099 2/00 4/00 7/00 SanfAig Bffitte
Figure 3.20: (A) Mean abundance (log x+1) of fish, (B) Mean number of fish species, (C) Mean abimdance of commercial fish and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Wallaga Lake over the three year sampling period. Lines denote standard error. 99 term was also significant {p<0.001. Table 3.7). A peak in mean abundance occurred at the upper location during October 1998, and was attributed to high catches of Acanthopagrus australis, Girella tricuspidata, and Mugil cephalus. The mean diversity of commercial species differed significantly among locations and sampling events {p<0.00l. Table 3.6), but the interaction term between these factors was not significant. Similar to some of the other estuaries it was not unusual for the cenfral and upper locations to have high mean diversity of commercial species compared to the entrance location (Figure 3.20). Highest mean diversity of commercial species was caught at the upper location during October
1997 and included species such as Mugil cephalus, Gerres subfasciatus, Girella tricuspidata, Meuschenia trachylepis and Meuschenia freycineti. A steady decline in commercial fish diversity and abundance occurred at all locations during the third year
(Figure 3.20).
3.4.4.7 Merimbula Lake
Merimbula Lake was also quite different in terms of its fish community to the other six estuaries, mainly as a result of high fish species diversity and low overall abundance of fish. A total of 5053 fish were caught, representing sixty-three fish species of which twenty species were considered of significance to commercial and/or recreational fisheries
(Table 3.2). In terms of abundance, Atherinosoma microstoma and Ambassis jacksoniensis dominated the assemblage. The highest numbers of commercial finfish species were
Girella tricuspidata, Acanthaluteres spilomelanurus, Meuschenia trachylepis, Myxus elongatus and Achoerodus viridis.
Only three species were caught only once in Merimbula Lake, and these were Hyperlophus vittatus, Apogon limenus and an Upeneus species. Nine fish species were unique to 100
Merimbula Lake. Examples include species from the Apogonidae family {Apogon limenus and Siphamia cephalotes), two Odacidae species and Syngnathoides biaculeatus.
Mean abundance did not differ significantly between localities, but there were differences among sampling events {p< 0.001, Table 3.5). There were no significant interactions between these two factors (Table 3.5). The lowest mean abundance was found at the enfrance location during October and July 1999, whereas the highest mean abundance was found at this location during Febmary 1999, due to high numbers of Ambassis jacksoniensis and also generally because many different species were caught that added to catch numbers. Samples taken during April 2000 had reasonably high mean abundances as well, particularly at the cenfral and upper locations, and this was primarily due to large numbers of Atherinosoma microstoma at both locations (Figure 3.21).
Differences in mean species diversity were also sfrongly related to time of sampling
(p<0.001), and the mean square values for sampling event was far greater than for the two- way interaction term which was also significant (Table 3.4). Thus, as with the pattem of abundance, low mean species diversity was found at the enfrance location during October and July 1999, compared to high mean number of fish species at the entrance during
Febmary 1999 and the cenfral location in April 2000 (Figure 3.21). High mean diversity at the enfrance of Febmary 2000 was due to three Syngnathidae species, six Gobiidae species and two Mullidae species being part of the fish assemblage. During April of the last year of sampling diversity of species ranged from five species from the Syngnathidae family, three Monacanthidae species, Favonigobius exquisites and two Odacidae species. In terms of mean abundance of commercial fish there was no significant spatial or temporal differences (Table 3.7, Figure 3.21). 101
(/^Abmianoeaffish (^Owergtyoffish
18- entrance central upper •2 15-
O) o S 12- c (0 •oc 3 ,fi I 9-1 la I' c c c 1-
3-
1 1 1 1 1 1 1 1— —I 1 1 1 1— —I 1— —I 1 1098 ^99 4/99 7/99 1099 2C0 4AX) 7AX) 1098 209 4/99 7/99 1099 2O0 4A30 7/00 (Q Abundance of oorranerdal fish (D) Diversily of ooimienjal fish 70.
I 60.
0) 5Q- E I 40. 8 •g 30. c 3 jaa S 20-1
10-
—I 1 1 1 1 1 r k T 1 1 1 T 1 1 1 1 1098 209 409 7/99 1099 2C0 4/DO 7/DO 1098 209 4/99 7/99 1099 200 4/00 7/DO Samplng Berts
Figure 3.21: (A) Mean abundance (log x+1) offish, (B) Mean number offish species, (C) Mean abundance of commercial fish and (D) Mean number of commercial fish species, caught at the entrance, central and upper locations of Merimbula Lake over the two year sampling period. Lines denote standard error. 102
Commercial species diversity experienced significant differences among locations and sampling events (p<0.01. Table 3.6), but the differences depended on time of sampling.
The highest mean diversity of commercial species was caught at the enfrance and central location during October 1998 (Figure 3.21). Diversity declined steadily at the enfrance location during the following year, until no commercial species were caught at the entrance in October 1999, while high commercial species diversity was caught at the upper location (Figure 3.21). Species caught included five Monacanthidae species (Table 3.2), and Girella tricuspidata.
3.5 Discussion
This study represents one of the first large-scale surveys of the estuarine fish communities inhabiting seagrass beds in a large number of ICOLLs in southem NSW over a long temporal scale. As such, it will provide baseline data for future research and monitoring programs.
3.5.1 ICOLL Fish Species Diversity and Abundance
A total of 209 366 fish were caught representing 48 families and 101 species. Thirty- seven species were considered to be of commercial and/or recreational value. Merimbula
Lake had the most diverse fish commimity with sixty-one species caught, while the lowest fish diversity was found in Coila Lake with forty-one species. In terms of abundance, the highest catch was from Wallaga Lake with 61492 individuals, and the lowest number of individuals was from Merimbula Lake (5430 individuals). Notably, the lakes with the most diverse fish communities, Merimbula Lake (61 species) and St Georges Basin (60 species), both had the lowest total catches when combined over all species (5430 and 103
14850 respectively). The remaining estuaries had similar levels of fish diversity with a range of 52-56 species caught, and the total numbers offish ranging from 22 153 to 41 732 individuals. The number of commercial species ranged from 17 species in Coila Lake, which is more often closed, to 20-24 species in the remaining lakes.
Overall, the fish communities ofthese ICOLLS in southeast NSW had many similarities to estuaries in other parts of Ausfralia. For example, large numbers of species from the
Ambassidae, Atherinidae and Gobiidae families dominated the catch in this study.
Numerical dominance by a few species, particularly species from the Atherinidae and
Gobiidae families, has been reported in many studies of estuarine fishes (Middleton et al.
1984; Loneragan et al 1989; Humphries et al 1992; Potter &, Hyndes 1994; Jenkins &
Wheatley 1998). This appears to be related to the ability ofthese individuals to exist in a range of salinity, turbidity and nutrient conditions (Potter & Hyndes 1999). In terms of species representation, the Gobiidae (12 spp) and Monacanthidae (9 spp) were the most diverse, followed by the Syngnathidae (8 spp). Studies conducted on the fishes in estuaries of the central coast of NSW (Hannan & WilHams 1998) and south coast of NSW
(Pollard 1994a) found similar results.
The fish communities of the southem region of NSW have previously been described as taxonomically depauparate (Pease 1999), compared to the nearby permanently open estuaries in NSW (Pollard 1994a), and the estuaries in the northem region of the state
(Gray et al 1996; West & King 1996; Hannan & WilHams 1998). However, this sttidy has demonsfrated that the shallow water seagrass habitats of southem NSW ICOLLs have a diverse range offish species. Nimibers of species (41 to 61) was comparable to numbers of species found in similar intermittentiy open systems, such as the Peel-Harvey (43 species) and Moore River Estiiary (27 species) in south-westem Ausfralia (Loneragan et 104 al 1986b; Young et al 1997). The intermittently open Swan River estuary was found to have 71 fish species in the shallow water seagrass habitat, but as it was sampled for five years with a range of sampling methods, results may not be comparable (Loneragan &
Potter 1990). Fish diversity within these ICOLLs were also similar to other estuarine systems in NSW that are permanently open, such as Clarence River (57 species) (West &
King 1996) and Botany Bay (McNeill et al 1992). The ICOLLS were less diverse than
Lake Macquarie situated on the central coast of NSW, where 80 species were found of which 40 species were of commercial and/or recreational value (Hannan & Williams
1998).
In comparison, between 20-24 commercially important species were found in the south coast estuaries. While this may be a reflection of Lake Macquarie's permanently open enfrance, it may also be a result of the presence of subfropical/warm temperate marine species that do not normally extend southwards along the NSW coast. It is also possible that the spawning grounds of some ocean-spawning species are some distance away from these estuaries (Miskiewicz 1987; Sheaves 1998). The low species diversity found in
Coila Lake, which was mostly closed, was to be expected due to the exclusion of marine species. Lower fish species diversity has been found in other estuarine systems in Westem
Australia (Potter & Hyndes 1994) and South Afiica (Bally 1987) that are closed to the ocean for extended periods of time.
3.5.2 Within - estuary variability in fish diversity and abundance hi terms of abundance of fish within each ICOLL, six had significant interactions between tiie factors of location and time of sampling. The exception was Merimbula Lake.
Anotiier striking feature was that for Lake Illawarra, St Georges Basin, Burrill Lake and
Coila Lake, 'location' within tiie lake was not significant, indicating the influence of 105 location within these estuaries on the abundance pattems of the fish community is relatively weak. The situation was remarkably similar for differences in species diversity, where even though there was interaction between location and time of sampling, the location within the lake was not highly significant in terms of species diversity for Lake
Illawarra, St Georges Basin, Burrill Lake, Coila Lake or Merimbula Lake. Hence, most of the variation in the abundance and species diversity of the fish communities is explained by temporal effects, and not by spatial influences. The influence of seasonal factors is not uncommon, as generally in southeast Ausfralia there are peaks in abundance and species diversity of estuarine fish communities in spring and early summer, mainly due to the influx of ocean-spawned individuals into the assemblages (Pollard 1984; West & King
1996). In this study temporal differences were driven by three main processes: firstly, by the recmitment of ocean-spawned individuals into the system during spring, summer and/or autumn months, particularly during October 1998; secondly, by a single substantial catch of a schooling species (e.g., Mugil cephalus in Burrill Lake): and thirdly, by differences in the abundance of the most common species (e.g., Atherinidae, Ambassidae and Gobiidae species) that are also typically schooling species.
The lack of influence of spatial factors, such as locations around the ICOLLS is quite surprising. Many studies have documented a declme in the number of species and abundance of fish with increased distance from the estuary mouth (Weinstein et al 1980;
Yanez-Arancibia 1985; Young et al 1997; Hannan & WilHams 1998), but this was not evident in the ICOLLs of SE Ausfralia. In comparable estuarine systems that are also intermittently open and closed, distinct changes in the stmcture of fish assemblages along the estuarine gradient have often been found. For example, research on the Peel-Harvey and Swan estuaries in south-westem Ausfralia have shown that there was a progressive decline in the number of species, density and biomass in the shallows of the estuary with 106 increasing distance from the estuary mouth (Loneragan et al 1986b; Loneragan «fe Potter
1990). The decrease in species diversity and abundance offish upstteam in an estuary has been related to a lack of ocean-spawned larvae away from the enfrance and/or decreases in salinity values. Loneragan et al (1986b) attiibuted higher species diversity at the enfrance of the estuary to the dominance of ocean-spawned young, and Haiman & WiHiams (1998) found that low species richness far from the enfrance and poor settlement of individuals was most likely related to the lack of ocean spawned larvae. Thus, it has been hypothesized that proximity to the ocean and relatively marine salinities, make the enfrance region a suitable habitat for marine fishes. This should lead to higher species diversity due to a lack of sfrong water movements to fransport larvae away from this region (Loneragan et al 1986b; Hannan & Williams 1998). This was not the case in the present study, where cenfral and upper locations within ICOLLs were often the richest sites in terms of species.
Fluctuations in salinity values have been documented as a major factor stmcturing estuarine fish communities (Loneragan et al 1986b; Loneragan & Potter 1990; Whitfield
1998). There will be an associated decline in ocean-spawned species with an increase in euryhaline species in the assemblage as salinity changes from close to seawater (~36ppt) at the enfrance to brackish and freshwater conditions (Loneragan et al 1986a; Young et al
1997; Sheaves 1998). A pronounced estuarine salinity gradient was not apparent in any of the estuaries sampled in this study (Figure 3.10), and this may be one of reasons there was no substantial change in overall pattems of diversity and abundance among the three locations. Salinity will limit the extent to which marine species will penefrate an estuary due to osmoregulatory sfress. Hence, if there is a lack of varying salinity within these lakes, this physiological parameter is not a barrier to marine species inhabiting the central and upper regions. Thus, while there were varying enfrance openings, from Merimbula 107
Lake and St Georges Basin being permanentiy open during the study period, and small duration of enfrance closures in Lake Illawarra and Wallaga Lake, to Coila Lake being closed for the majority of the time, within ah ofthese lakes there was quite similar salinity values at each location throughout the estuary. Most importantly, when tiiere were changes in salinity values the change was consistent across the locations. Also, as tiie salinities within these ICOLLs were often intermediate values within tiie tolerance range of many estuarine and marine species, and were rarely below 20ppt, the diversity and abundance of species was quite stable spatially throughout the estuaries.
A lack of salinity gradient is related to the geomorphology and hydrology of these estuaries. These lakes are regarded as small in size (Zann 2000) with little tidal action
(Roy 1984). There is limited freshwater discharge into these systems, as none of the estuaries studied are part of a major river system (West et al 1985). Unlike the situation in South Afiica where water levels and salinity values vary considerably seasonally and from year to year, due to a markedly seasonal rainfall pattem (Bally 1987), the NSW south coast lacks a pronounced rainfall pattem. Thus, combined with little seasonal exfremes in salinity, all these factors contribute to relatively stable hydrological conditions in the
ICOLLS of south-east NSW and thus create favourable conditions around the perimeter of the lakes for many of the fish species that inhabit these environments. Other ICOLL systems have been found to have high diversity of fish species at centrally located sites, such as the Swan estuary in Westem Ausfralia (Loneragan et al 1989). In this estuary, the mean number of species was highest at sites located in the middle estuary, at a distance
25km from the enfrance mouth, and this was suggested to be the result of relatively high salinities at these sites enabling stenohaline species to penefrate and survive in this region
(Loneragan e? fl/. 1989). 108
Water movements may also be playing a significant role in the fransport of new recmits within the ICOLLs of southem NSW, and thus, on tiie diversity and abundance pattems of fish species. The majority of these lakes are relatively shallow and as tidal currents and movements are quite weak, wind-induced currents are likely to be the main water fransport mechanism. It has been proposed that larvae will settle m the first seagrass beds
encountered (the 'stay and settle' model by Bell et al 1988), and tiiat it is unlikely that
recmits will move between seagrass beds when they are less than 40nim in length
(Worthington et al 1992). Hence, the presence of individuals less than 40nim, including
ocean-spawning species, at the central and upper locations indicate that wind-induced
water currents are sufficient and sfrong enough to fransportlarva e away from the enfrance region, and to cause a mixing of new recmits around the estuary.
Therefore, the differences in the pattems of species diversity and abundance found in the
ICOLLs of SE Ausfralia, to those in Westem Ausfralia, may be related to two key
differences between these systems. Firstly, while marine species are a dominant
component ofthese estuaries, the distances from the estuary mouth to the upper regions are
much less in the SE Ausfralian ICOLLs, compared to, for example, the Swan River estuary
(Loneragan & Potter 1990). Secondly, the salinity range is less extteme in the ICOLLs of this present study compared to estuaries such as the Peel-Harvey estuary (Loneragan et al
1986b) and the Swan River estuary (Loneragan & Potter 1990).
3.5.3 Variability in patterns of species diversity and abundance
There was considerable variability in species diversity and abundance within each estuary but there was also a consistent lack of any clear pattem of these factors, not only within individual estuaries but also across the seven estuaries. No generalizations could be applied to the timing of peak diversity or abundance across all seven estuaries, with peaks 109 occurring at different times of the year at different locations, and at the spatial scale of years. It is quite common to find differences of an order of magnitude m abundance between sites of apparentiy sraiilar habitat, and from year to year at the same site (McNeill et al 1992). In the present study, the abundance of most species fluctuated significantiy among localities and with time, but displayed no consistent inter-estuary pattem. Ferrell &
Bell (1991) also found in a study of 3 estuaries in NSW there were large and mconsistent differences in the abundance of individual species. There was little evidence for consistent changes in abundance or diversity in all seven estuaries, and uniform changes in abundance or diversity at all three sites within an estuary were rare. This supports recent evidence that has shown similar variability at the spatial scale of estuaries (McNeill et al
1992). Large and inconsistent intra- and inter-estuary differences in abundance have been recorded as a prominent feature of many studies investigating fish assemblages in seagrass beds (FerreH & BeH 1991; Ferrell et al 1993).
Inconsistent differences in abundance among estuaries could be due to differential recmitment of some species to different estuaries. Many species have a pelagic larval phase and are characterised by large fluctuations in recmitment. It is well known that many species have seasonal pattems of abundance (Young 1981; Loneragan et al 1989;
Connolly 1994), and it is improbable that concordant temporal changes in abundance of all species across different localities occurs (Ferrell et al. 1993). Indeed in this study, the recmitment of species was highly variable from year to year and within estuaries, with peak recmitment occurring in October 1998 across all estuaries but with weak recmitment noticeable the year before and after (see Chapter 5). Also, seasonal increases in species diversity during spring/summer were not always evident across the three years, and most notably the settlement of new recmits did not necessarily occur at the entrance site.
Indeed, for these ICOLLs making a prediction of where new recmits of both marine and 110 estuarine species would be found would be exfremely difficult, and there were no consistent sites of high species diversity or consistent recmitment. There was a general lack of seasonal pattem in species diversity and abundance. Overall winter (July) samples had lower mean abundance and species diversity. However, this was not always consistently the case. For example, in Wallaga Lake mean abundance at the enfrance in
July 1998 was higher than the abundance caught in summer (Febmary) 2000. It was quite common for the spring, summer and autumn samples to be relatively similar in diversity and abundance due to recmitment of different species during these months, and a number of species were caught year round in different size compositions.
This chapter has considered the spatial and temporal variability in species diversity and abundance of fish in the shallow water seagrass habitats of seven ICOLLs in SE Ausfralia.
To summarise, it was found these estuarine systems supported a diverse range of fish species, comparable to other intermittently open estuaries, and they should be considered significant nursery areas for many marine and estuarine species. There was little difference over the scale of lOOkms in the number of species caught in each ICOLL. The main exception to this was for Coila Lake, where the exclusion of marine species occurred when the enfrance was closed. The other noticeable difference was the relatively low overall abundance of fish in St Georges Basin and Merimbula Lake, compared to the other five ICOLLs, even though these two estuaries had the highest diversity of fish species.
Lastly, there were no clear pattems to the variability of species diversity and abundance, spatially and temporally within the ICOLLS, and between them. One of the most important findings was the lack of spatial influence on diversity and abundance pattems within the ICOLLs. Temporal influences drove much of the observed significant differences in species diversity and abundances within the ICOLLs, and the main temporal differences could be related to a particularly high recmitinent event in 1998, to a single Ill high catch of a particular species, or to differences in the abundance of the most common species. 112
Chapter Four
Community changes in the fish assemblages of six intermittently closed
and open estuaries of SE Australia.
4.1 Introduction
Chapter 3 dealt with spatial and temporal pattems in species diversity and abundance offish in seven ICOLLs of SE Australia. In this chapter, large-scale pattems in the fish assemblages of these ICOLLs will be investigated, and issues such as rarity and the conservation and management of these estuaries will be discussed in relation to pattems of ICOLL fish community composition. Information on multi-species distributions is becoming increasingly important for the ecologically sustainable development of marine resources, particularly fisheries management and the conservation of representative marine ecosystems (Fairweather
& McNeiH 1993; Agardy 1994; Fairweather 1999).
Changes in fish community stmcture within estuaries have often been related to a categorisation of estuarine fish based on specific spatial and temporal habitat usage (Wallace et al. 1984; Lenanton & Potter 1987; Whitfield 1998). Generally, estuarine fish communities are comprised of a mixture of ecological groupings that include freshwater species in the upper reaches, euryhaline species that complete their entire life history within the estuarine system, and marine spawning species whose young primarily use the entrance region seasonally as nursery areas (Loneragan et al 1989; Loneragan & Potter 1990), resulting in a considerable degree of spatial segregation within estuaries (West & King 1996). The objective of tiiis chapter is to assess if the pattems and associations of fish community 113
compositions of the shallow water seagrass habitats of six ICOLLs in southem NSW, changed
spatially and temporally within and between ICOLLs.
Information regarding the composition offish communities in ICOLLs of NSW is lacking (see
Chapter 2), and the studies that have been conducted in this region have not focused on local
community changes within these types of estuaries (Ferrell et al 1993; McNeill &
Fairweather 1993). Research on intermittently open and closed systems in Westem Australia
and South Africa have shown that the number, composition and abundance of species can be
related to whether an estuary has been closed, and the timing and duration of closure (Bennett
et al 1985; Bennett 1989; Young et al 1997; Potter & Hyndes 1999). It appears that esttiaries
which remain closed for extended periods show much reduced fish densities and species
richness, and the fish assemblage will be dominated by estuarine and freshwater species as
larval recmitment of marine spawning species is dismpted by entrance mouth closure
(Loneragan & Potter 1990). Previous research on the shallow water seagrass fish species of
ICOLLs (see Chapter 3) concluded there was not the expected decline in the number of
species and abundance of fish with increased distance from the estuary mouth, which has been
documented for many other estuarine systems (Weinstein et al. 1980; Yanez-Arancibia 1985;
Haiman & Williams 1998). Hence, investigation on fish community composition at the
entrance, central and upper locations within ICOLLs over time is warranted to determine what
is driving diversity and abundance pattems within these systems.
Information about the habitat use, recmitment and biodiversity is essential in providing a broader understanding of the status of fish populations in the estuaries of southem NSW, and guide the protection of estuarine-based fisheries. The present state of knowledge on the conservation status of marine and estuarine fishes is relatively poor (Pogonoski et al 2002). 114
Not only is there limited biological and ecological information for marine communities, but criteria for assessing the conservation status of marine species has not been adequately developed (AIHson etal 1998; Chapman 1998; Chapman 1999; Fairweather 1999).
Rabinowitz (1981) and Rabinowitz et al (1986) developed a core model for the determination of rarity, of which there are 7 forms of rarity on the basis of dichotomous measures of large/small abundance, wide/narrow geographic range and broad/restricted requirements for habitat. Rarity relates directly to populations that have a low local abundance and/or small geographic range, whereas vulnerable or threatened species are those populations that are in decline either naturally or due to anthropogenic influence (Gaston 1994). The application of this model has been successful in studies of plants and mammals, but the application to fish species may prove difficult due to the nature of fish populations and problems with adequate sampling. For fish fauna determination of rarity is very difficult, due to particular life history characteristics, such as variable and dynamic recmitment and distinct life history stages (e.g., planktonic larvae, juvenile and adult). In a recent examination of the conservation status of
114 threatened and potentially threatened marine and estuarine fish species, 53 ofthese taxa were listed as data deficient (Pogonoski et al. 2002). This lack of information results in an unquantitative approach to reserve selection in NSW, and the continuation of a lack of specific criteria and goals for the conservation management of estuarine and marine fish communities.
Importantly, information on fish community stmcture may help decide the appropriate scale at which to manage marine and estuarine communities in this region. Effective spatial management of marine resources will need to consider the ecological pattems at both regional and local scales, and this will depend on the species and processes being considered. 115
4.2 Methods
4.2.1 Field Sampling
The data used for this chapter is from the sampling program described in Chapter Three. Data from six estuaries are included for this analysis of community pattems (Lake Illawarra, St
Georges Basin, Lake Conjola, Burrill Lake, Coila Lake and Wallaga Lake). The partial data set for Merimbula Lake was not suited for the analytical techniques adopted
4.2.2 Data Analysis
Community stmcture was examined by multivariate techniques using the PRIMER 4.0 software (Plymouth Routines Multivariate Ecological Research). This allowed investigation of the similarities in the fish assemblages between locations within estuaries, between seasons and years, and similarities between the six estuaries. Hierarchical agglomerative classification analysis and multi-dimensional scaling (MDS) ordinations were employed to examine pattems in the stmcture of the fish community data. Replicate data were pooled and transformation (x
) used to emphasize the distribution of less common species in the analysis (Clarke 1993).
Similarity matrices were calculated by the use of the Bray-Curtis similarity measure (Bray &
Curtis 1957). This dissimilarity measure was chosen as it is not affected by joint absences and gives more weighting to abundant rather than to rare species. It has proven to be robust and has consistently performed well in preserving 'ecological distance' in a variety of simulations
(Faith et al 1987). The data was subject to cluster analysis using group average linking to constmct hierarchical agglomerative dendograms. In order to view spatial relationships, ordination employing non-metric multi-dimensional scaling was performed to generate two- 116
dimensional ordination plots of the data. Even though in the majority of cases the associated stress levels were high (Clarke 1993), the two-dimensional plots were used, as they provided the best interpretation of the results.
Inverse analysis was performed for each data set to explore species relationships to each other.
Replicate data was pooled and transformed (x ' ).
The assumption of multivariate normality is likely to be violated by the data due to the fish samples being characterised by small numbers with many zeros. A non-parametric analogue with no assumption of normality is the analysis of similarities (ANOSIM), which compares ranked similarities between and within groups selected a priori by using a randomization test for significance (Clarke 1993). The null hypothesis for the ANOSIM test is that there are no differences in the community composition between the assigned groups. All ANOSIM tests involved 5000 simulations with the PRIMER package.
SIMPER (Similarity Percentages) analyses (Clarke 1993) using the PRIMER package were conducted to determine which species were primarily responsible for differences across locations and sampling events, and between estuaries. The SIMPER procedure determines the average contribution of each species to the similarity (typifying species) and dissimilarity
(discriminating species) between groups of samples. A ratio is then calculated based on the standard deviation of the dissimilarity values for a species and the average contribution of each species. A species that consistently contributes to the separation of two groups has a high ratio. 117
4.3 Results
This section investigates community changes in the fish assemblages of six ICOLLs. For a species list and the abundance of individuals for these estuaries refer to Table 3.2 in Chapter
Three.
4.3.1 Patterns in fish communities within and between estuaries
Multivariate analysis (classification and ordination) indicated that there were differences in the delineation of the fish community at the three locations sampled within each of the six estuaries. For three of the estuaries, Lake Illawarra, St Georges Basin and Lake Conjola, there were differences in the fish communities caught at the entrance, central and upper locations
(Figure 4.1). While overall this separation was apparent, there was also some overlap between these groupings, reflecting a number of "cross-over" species between groups. Also, the samples from the central and upper locations were more similar to each other, than to the enttance samples (Figure 4.1).
For Lake Illawarra and Lake Conjola there was a significant difference in the underlying species composition between locations (ANOSIM, P<0.001). Samples from the enttance location were significantly different to both the centtal and upper locations, but the central and upper locations were not significantly different from each other. Assemblages of fish from each location within St Georges Basin were all significantly different (ANOSIM, P<0.001). 118
For Burrill Lake and Wallaga Lake there was a tight clustering of aU samples (Figure 4.1).
This indicates a high degree of similarity in the fish assemblages at the entrance, centtal and upper locations within these two lakes. Factors such as site, season and year had Httle influence on the abundance and distribution of fishes within these two estuaries. Despite this, there were slight and progressive changes in the fish community stmcture within Burrill Lake, as the entrance and upper samples showed significant differences in community composition
(ANOSIM, P<0.001). Wallaga Lake had no significant differences in the fish assemblage from the entrance, central and upper locations (ANOSIM, P>0.0\). Site-based grouping was weak within Coila Lake (Figure 4.1), with no significance differences in fish community stmcture between the entrance, enttance and upper locations (ANOSIM, P>0.01). 119
Lake Illawarra St Georges Basin •
^^:
stress = .20 Stress = .24
Lake Conjola Burrill Lake •
• •
stress = .18 stress = .16
Coila Lake Wallaga Lake
• • • • • • - • • • V-^^ / • •
stress = .19 stress = .17
>- entrance ^ central ^ upper
Figure 4.1: Plots of multi-dimensional scaling based on fish communities caught during each sampling event at the entrance, central and upper locations within the six estuaries. 120
For all six estuaries there was a failure to show a distinct seasonal signal, with the effect of year exhibiting a greater influence on fish community stmcture (Figure 4.2). In Lake
Illawarra, the fish community was different between years, but the spring, summer and autumn samples from each year were more similar to each other than to respective seasonal samples from other years. The only distinct seasonal pattem was that winter samples were outliers in the ordination plot (Figure 4.2). Yearly effects were also apparent in St Georges
Basin and Lake Conjola, with the third year samples showing differences to the first and second year samples in terms of their fish community composition (Figure 4.2). Seasonal differences were apparent in St Georges Basin, through the clustering of the spring samples from Year 1 and 2, but like Lake Illawarra, within year samples were more similar to each other than to relational seasonal samples. The seasonal and yearly pattems in Burrill Lake were also quite similar to St Georges Basin with Year 1 and 2 spring samples showing a high degree of similarity. The decline in abundance and diversity during the third year was evident, as well with a spring sample being an outlier in the ordination plot with the winter samples from Year 2 and 3 (Figure 4.2). Thus, the major differences in abundance between years probably influenced the results of the MDS. Coila Lake had noticeable differences in the fish communities between years, and the effect of year was the major force stmcturing the fish community (Figure 4.2). Seasonality and yearly effects were weak in Wallaga Lake and the fish community displayed few differences in composition between seasons and years
(Figure 4.2). The third year samples cluster as an outlier in the ordination plot, due to low abundance and diversity in this catch. 121
Lake Illawarra St Georges Basin wi1
sp2 spl
wi2 wi1 su2 au2 wi3 aul sul wi2
Stress = .15 Stress = .16
Lake Contola Burrill Lake \vvi2 su2 >v X"^^ /Vvi3 Vy Sp2/_„.-rr-) (Jp^^ v^2 ^^;;:::^ / wi3 I au3 spSi y^ sul sp3 /sp1 / / su2 a"1 su3\ \,.si^.,^ / aul / wi2 I wi1 \ au3 \ au2 \ su1^/ ^—^ Stress = .18 Stress = .14
Coila Lake Wallaga Lake
wi3
Stress = .13 Stress = .01
Figure 4.2: Two-dimensional plot of multi-dimensional scaling of fish community data for six estuaries, showing effects of seasons and years. Locations have been pooled. sp=spring, su=summer, au=autumn, wi=winter. Nimibers refer to each year of sampling. 122
4.3.2 Species-Site Associations
4.3.2.1 General Overview
In this section, pattems in species associations of the entrance, centtal and upper locations within each estuary were investigated. A matrix of relative abundance (log ttansformed values) caught at each location during each sampling event, was constmcted against a dendogram of the inverse analysis of species similarities for each estuary.
Inverse analyses of species similarities for each estuary revealed that there was a common pattem to the clustering of species similarities across the estuaries (Figures 4.3 - 4.8). There were similarities in the main clustering of the fish assemblages between lakes, however for individual estuaries there were also obvious differences in species associations. The matrixes demonstrated that there was a group of species common and abundant in most locations and estuaries, and which are therefore a core feature of the shallow water fish fauna from these south coast estuaries (Figures 4.3 - 4.8). This 'core' group includes species from families such as Atherinidae, Ambassidae and Gobiidae, as well as marine spawning species such as
Acanthopagrus australis, Girella tricuspidata, Pelates sexlineatus and Monacanthidae species. The remaining species were captured either rarely or in low numbers.
Notably, the MDS plot of species also indicated that the majority of the fish species within each estuary had a high degree of association with each other (Figure 4.9 - 4.14). In most instances, those species that were caught rarely or in low numbers were the only species clearly separated from the 'core' fish fauna (Figure 4.9 - 4.14). An exception to this occurred 123
Group J Entrance Group 2 Central Group 3 Upper Species r 1 1 1 H.vittatus • B.jacksonianus O Philypnodon sppl • S^maculata 0 R.sarba o • A.flrmamentum © P.signatus © P.dentex • S.ciliata • S.flavicauda • P. arsius • F.commersonii • P.vittiger • N.ayraudi o o E.armatus o S.lineolatus © U.tragula • • S.fiiscescens • • H.aus trails • O 0 © • • P.signifer •.o©oooooo M.chinensis • • • © • P.saltator © © o . . © 0 , o o D.punctulatus © • O O o o . . o • F.exquisites 0 © o . o A.australis . . o • . O © O O 0 o o O 0 o o o . © o M.cephalus 0 o o © o © © © o . . o O O 0 o M.trachylepis o o o © . © o o O G.tricuspidata © O O O 0 o o• o©o0.o oo o O © © 0 . o o o M.freycineti • 0 , o o © o , © . o © o o . © 0 P.sexlineatus o o o o o o o • © . © O O 0 © • • o © © C.aus trails © . o • • • . o o • • R.macrostoma • o o • o o . © . . O O © 0 A.frenatus • • 0 o o o O 0 A.elongata 0 © o © O . 0 © O M.elongatus • © . O . 0 • o M.argenteus • © . © o T.hamtltoni . o • • • . © . . © A.jacksontensis • . o o . • o o • o •OOOOOOOO o . © o . o o o A.mlcrostoma • o o o o ©©OOO0OO o © © . • o © • A.tamarensis © © o o . 0o©0©..o 0O0OO •©©© o oo G.semivestitus o • O.O .00.00000 o o o o • o A. bifrenatus 0 . 0 o . o o . O . O.O G.subfasciatus • o © o o © © .oooooo.ooo.o P.grandiceps © © • oooooooooo©©oo . © O O O O O o P.olorum 0 • © o . © o ooo©oooooo U.carinirostris © o © • .© oo.o. © o . oo.o. . . A.spilomelanunis • © 0 . B.krejfti • © . S.granulatus © F.lateralis o © © . © © • © o . . P.lupus • © © o © o . • © • . T.glaber 0 • • • • • • V.phillipi « . © © • A.viridis © o • © • • S.nigra o © o o V.poecilolaemus • © O O 0 0 0
Figure 4.3: Shade matrix for 56 species and 36 samples (separated on basis of location and sampling event) from Lake Illawarra. Abundance of species has been categorized (double square root transformation from Bray-Curtis similarity) and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Symbols of increasing density shown by • O O O • 124
Group 1 Entrance Group 2 Central Group 3 Upper
Species O. anolius B.jacksonianus U. tragula C.macrocephalus © H.aits trails M.strigatus C.auratus H.whitei Lgenivittatus F.exsquisites Abudefduf spp. A.frenatus S. leiura D.punctulatus © . H. breviceps P.vittiger © R.sarba © T.gavialoides © B.kreffti A.bifrenatus H.vittatus E.armatus A.mlcrostoma 0 . o o M.argenteus 0 o © . © © C.aus trails 0 P.grandiceps O S.fiiscescens © © S. obtusata 0 O.acroptllus P.urvillii T.hamiltoni A.viridis . o © © © N.ayraudi © 0 © 0 S.lineolatus o o . T.glaber © © A.spilomelanunis © o o © P.saltator o o 0 © © © © S.granulatus o 0 © Meuschenia spp. o 0 © S.nigra o o o o © A.australis • • 0 o 0 o © M.cephalus o o S. argus o o o o O 0 A.tamarensis © © 0 0 0 P.olorum © © o M.elongatus © © M.chinensis © F.lateralis © o © © o o o o © P.lupus o o o © 0 © © © © 0 © A.elongata O o © o • o © G.semivestitus © o o © . o o o R.macrostoma © © 0 0 © o A.jacksontensis O O O o o o o o o • o o © o © o o o o • o o M.trachylepis o © . o coo o © o o © o o • o G.tricuspidata O 0 0 o . o o o o © 0 • o o © © o © O O 0 o . © M.freycineti © © . o o © © © 0 © o o © . . © o o 0 © P.sexlineatus o © o © . o o o o o o o o o © o o © O O © © V.phillipi o © © © . o © © O 0 U.carinirostris 0 o o © © © © © 0 0 0© © © V.poecilolaemus o o o © o o . © o o o O O Q O o o o Figure 4.4: Shade matrix for 60 species and 36 samples (separated on basis of location and sampling event) from St Georges Basin. Abmidance of species has been categorized (double square root transformation from Bray-Curtis similarity) and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Symbols of increasing density shown by • © O O O • 125
Group 1 Entrance Group 2 Central Group 3 Upper I ' ^ ^ Species T.glaber • G.maculatus * P.dentex * S.flavicauda * A.reinhardtii • H.aus trails Sphyraena spp. • S.fiiscescens • Lgenivittatus © 0 B.kreffti 0 ^ A.striatus • T.hamiltoni • E.armatus ® • A.spilomelanunis ® ® S.lineolatus • V.phillipi • 0 c.auratus O D.punctulatus • ® R.sarbaH.compressa © .O0 S.neopilchardus A.bifrenatus O.. .0 ©O.. ©.©0 F.exquisites , O . O . O 0 o Philypnodon spp. o . o o . o o . M.chinensis " 0© ©©O©© .0 M.argenteus O © . © . M.freycineti ,©OO0. O 00O. . © . M.trachylepis ,0© . ...O OO ©© 0 P.sexlineatus OO OO ,00 ..O © A.frenatus ,.0.00© . P.olorum ..O©© ,.©.0 O ©O O O Largentea © O O O O O O A.tamarensis © OO©. O. •©©.©. OOO O 0.©0 A.australis OO © . ©OOO©© 00©.0 0 OO G.tricuspidata © OO. OO ©0OOOO OO.0O ©O 0 0© G.subfasciatus © . © OO00.O OOO © O M.elongatus © . ©000©000 O0.0OOO. G.semivestitus O© O OOOO OOOOOOOOOOOOOOOO® A.jacksontensis OO O OOOOOOOO©. . .OO .0 . P.signifer O OO O OOOOOOO ©OOOOO.O P.grandiceps O O. O.O OOOOO0OOOO OOOOOO.OO.O.. R.macrostoma © O 0© OOOOOOOOOO0OO0OO OOQO M.cephalus O.O 0.O.OOO . OO0© U.carinirostris OOO© .0 0 O.O.©.© ©© O.O. 0.0 © H.vittatus • N.ayraudi 0 © . Meuschenia spp2 O . * S.nigra © O O • P.saltator 0..0 .O. O O ... A.viridis OOO 0 • • A.elongata OOOO O © A.mlcrostoma O O O O O O © C.australis O F.lateralis 0000©0000© 0 O P.lupus O .00 V.poecilolaemus .©©0.©©» • . .
Figure 4.5: Shade matrix for 41 species and 36 samples (separated on basis of location and sampling event) from Lake Conjola, Abundance of species has been categorized (double square root transformation from Bray- Curtis similarity) and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Symbols of increasing density shown by • O O O • • 126
Group 1 Entrance Group 2 Central Group 3 Upper I 1 1 1 Species A.reinhardtii • Scarus spp. • S.lineolatus • A.spilomelanunis © © F.commersonli © H.vittatus • E.armatus © S.granulatus © • S.nigra • O © O Largentea © • P.dentex • R.sarba . F.exquisites © H.compressa © • Meuschenia spp. . © © . Philypnodon spp. . . P.saltator O © A.viridis • © . . T.hamiltoni © . . . A.australis . . . © O . A.bifrenatus © © .0 A.flrmamentum © M.chinensis O O . . Scorpis spp. . S.fiiscescens . 0 . © © P./wpiis © © © . © . . r.^/aier ...©0 0 . . A.elongata O • c.australis • . . .0.0©© ©.. F.p/i/%/ .0.0© A.frenatus • © © O © H.australis © O P.olorum © O O. ©OO©. G.subfasciatus . . © ...©• M.argenteus . . © © ©.©© P.signifer . O O . © A.mlcrostoma OO OO. ©.O © O O O0 M.elongatus OOO O . O O M.cephalus O0O© O.O.O© 0. . A.tamarensis ©©©.O. 0©0 ..O O© A.jacksoniensls 000©0 OOOO OOOOO.OOOO 0000000©00000 D.punctulatus © © ©©©©.,0©.©© G.semlvestitus .©O . . ©,0 ©O© 00©0©©©0 M.freycineti © O .0©0© © .OOO©©© ©. ©. O© © G.tricuspidata O ©©© O©©0 .O OOOOO0O©© 0.0.0©0000 P-sexlineatus 0©0 . ©©OO O©O©OOO©OOOO0 O00 .0©©. M.trachylepis . O, ©OO ©©OO OOO .0 © 0O©O© . P.grandiceps .O O O© O 0.0©.0 OO 0.©00.00. R.macrostoma .© . .O. OO © . OO. OOOO.OO. U.carinirostris .. © . ©..OO© .O ©©.0000.©00 F.lateralis OO.O . O S.argus O O . © © V.poecilolaemus 0O©O0©. O© . O
Figure 4.6: Shade matrix for species and 36 samples (separated on basis of location and sampling event) from Burrill Lake. Abundance of species has been categorized (double square root transformation from Bray-Curtis similarity) and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Symbols of increasing density shown by • 0 O O # # 127
Group 1 Entrance Group 2 Central Group 3 Upper I \ I I Species G.holbrookl O © F.lateralis O © © P.fiiscus • P.signifer • G.greyi • P. arsius • R.calcaratus © T.hamiltoni • . • B.kreffti • • Largentea • c.australis • H.regularis © S.flindersi © O P.jenynsii • © M.elongatus ® © S. ciliata . © O T.glaber © . © . . . . A.reinhardtii • M.cephalus © Philypnodon spp. © • © © G.tricuspidata • • O ® A.viridis O M.freycineti © • M.trachylepis • M.chinensis • • C.australis • F.exquisites OOOOO ©OOOOOO A.mlcrostoma OO.OOOO OOO OO OOOO OO O. OOOOO OOOO A.tamarensis * ©O 0©0.0 O.OO A.elongata 0 OOO O OO0 OOOO. G.semivestitus O O0O O OOOOO© .0 0©00 A.australis 0©00 OO . O OO H.australis ©© O O OO OO OO OO P.grandiceps • .0O0 OO. O0 OOOOOOOO A.bifrenatus O 0 0.. . © P.o/orMm O 0 O O © © U.carinirostris 0 0.0 0 O OOOOO O OO0O. A.frenatus OOO R.macrostoma • • • O Kp/ii7/(p/ .00 . © V.poecilolaemus . ©
Figure 4.7: Shade matrix for species and 36 samples (separated on basis of location and sampling event) from Coila Lake, Abundance of species has been categorized (double square root transformation from Bray-Curtis similarity) and represented by sjmibols of increasing density, and ordered on the basis of cluster analysis of species. Symbols of increasing density shown by • © O O • • 128
Group 1 Entrance Group 2 Central Group 3 Upper
Species 1 1 1 1 Microcanthidae spp. • O.anoltus © Philypnodon sppl © H.australis . A.reinhardtii • C.argyropleura 0 S.fiiscescens © P.urvillii • • T.hamiltoni • T.glaber • P.lupus • o M.argenteus • o o . © N.ayraudi © A.spilomelanurus o o B.kreffti © • P.jenynsii c A.viridis © 0 A.elongata o • • • o F.lateralis © • © • © 0 P.saltator . o o o o • o o o o © o A.tamarensis o . o 0 0 o 0 o 0 © o o o o o o o o A.bifrenatus 0 © • o © o o o o . o • o 0 F.exquisites • o o © © o o 0 R.sarba © © © 0 o o o S.granulatus o © © D.punctulatus 0 • • • o o © © M.elongatus © o © • o o 0 o o © Largentea © • © © o • o o o P.grandiceps © © • © 0 • o . o o o o o o o A.mlcrostoma O © o o o o o © o o o o o • • o o o o A.jacksoniensls 0 G.semivestitus 0 o o O o o © o o 0 o o o o o o o o o o o o o o o o o o o o o OOO R.macrostoma o o o o o o © o © © o o o o o o o o o © © M.cephalus o o © o o © o o © • © o o . © P.signifer o © o o o o © o o o • o o o o o o G.subfasciatus o © • o o o © o o o o 0 o © © © © C.australis 0 © © © • © o © o 0 o © © o o © © • M.trachylepis © • • o o o • • © o o o 0 o o o © o o • © M.chinensis • © © © © © © o © • o • o o o o o P.olorum 0 o o © • o o o o o o • o 0 o • o o o o o o A.frenatus • © © © o o o o o © o o o o o • 0 o o M.freycineti 0 0 o © o o o © © o © • © o o • o • o . P.sexlineatus 0 o © o o © o o o o • o © o © o • 0 © © o o © . o A.australis o o o o © o o o © o © © o © © © o © o © o © © o o G.tricuspidata o o o o o o o © o o o o o o o o o o o o o o • o o o © . U.carinirostris 0 o o o © © © o o © o o o o o o o © o o o © o o © o o o © . V.phillipi o • © o • o © o o 0 o o o o o o o 0 o 0 © o o © . 0 . D.lewini • E. australis © o P.dentex o • o S.argus • • © © V.poecilolaemus o © • • © © o
Figure 4.8: Shade matrix for 52 species and 36 samples (separated on basis of location and sampling event) from Wallaga Lake, Abundance of species has been categorized (double square root transformation from Bray- Curtis similarity) and represented by symbols of increasing density, and ordered on the basis of cluster analysis of species. Symbols of increasing density shown by • © O O • • 129
in Burrill Lake where all the fish species captured clustered sttongly together (Figure 4.12), showing only slight separation of the core group of species.
4.3.2.2 Core group of species
Thus, each estuary had a group of species that clustered tightly in ordination space, and these constituted the 'core' group of associated species of that lake's fish fauna (Figure 4.9 - 4.14).
The core group for a particular estuary was comprised of species that were common to all locations, and often consistently caught in high numbers during the majority of sampling events (>75% of all sampling events). There were also species making up the core group which were common to all locations but varied greatly in abundance.
In most estuaries there were highly abundant species, and it was commonly only one species that dominated catch numbers, usually a species from the Atherinidae, Ambassidae or
Gobiidae families. In St Georges Basin and Burrill Lake, Ambassis jacksoniensis was caught most consistently (Figure 4.4 & Figure 4.6). In Coila Lake Atherinosoma microstoma dominated the catch (Figure 4.7), and in Wallaga Lake, there were three species that were caught 90% of the time in high densities; Ambassis jacksoniensis, Gobiopterus semivestitus and Redigobius macrostoma (Figure 4.8). Lake Conjola differed to the other estuaries in that there were no species that could be considered to be caught in high numbers at each location during most sampling events. While there was a group of species (e.g., Gobiopterus semivestitus, Pseudomugil signifier and Redigobius macrostoma) that were caught at the centtal and upper locations, they were not caught as consistently at the entrance location
(Figure 4.5). 130
These 'core' groups also contained species caught in lower abundance than those species mentioned above, but were still caught at all three locations. The number of species that comprised this group ranged from 10 species in Burrill Lake to 21 species in Wallaga Lake.
The consistency of capture of these species differed within estuaries and among them, from being caught during all sampling events to being caught approximately 60% of the time at a location or within a lake.
For most estuaries, the presence of these species at all locations explained the high degree of similarity of the fish fauna throughout their systems. Overall a high percentage of species caught within each lake were found across the three locations. The highest percentage was found in Wallaga Lake, with 62% of species being common to locations at the entrance, centtal and upper locations. This explains high degree of similarity of the fish fauna within
Wallaga Lake (Figure 4.1 & Figure 4.14). 52% of species in Lake Illawarra were caught across all localities, and Burrill Lake and Lake Conjola both had 43% of their fish fauna common across the three sites. The entrance, central and upper sites of St Georges Basin shared 37% of all species, with the locations within Coila Lake having the lowest shared percentage of species at 27%. 131
A.firmanientum P,signatus P,dentex P,arsius S.ciliata F,conunersonii P,vittiger S, flavicauda M,chinensis N.ayraudi
U,tragula E.armatus S,lineolatus
S,granulatus A,spilomelanurus T,glaber V,phillipi A,viridis S,nigra V,poeci]olaemus
S,fuscescens D.punctulatus A,bifrenatus A,australis B,kreffti Csubfasciatus H,vittatus M,cephalus P,grandiceps M,trachylepis R,sarba P,olorum Philypnodon spp. Ctricuspidata U,carinirostosis M,freycineti P,sexlineatus P,lupus Caustralis F,lateralis R,macrostoma A,elongata M,elongatus T,hamiltoni A,jacksoniensis A,microstoma A,tainarensis Csemivestitus
Figure 4.9: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, cenfral and upper locations during each sampling event in Lake Illawarra, Data was 4 root transformed, Sfress = 0.17 132
M,argenteus M.cephalus Meuschenia spp, A,bifrenatus M,chinensis A,viridis E,armatus A,elongata S,granulatus A,microstoma P,lupus P,saltator B,kreffti Caustralis A,spilomelanurus
H,vittatus Abudefduf spp. A.frenatus T, gavialoides Cauratus P.vittiger F,exquisites R,sarba H, whitei L,genivittatus Cacroptilus P,grandiceps P,urvillii Csemivestitus S,fuscescens R,macrostoma S,obtusa A,jacksoniensis S,nigra M,trachylepis S,leiura Ctricuspidata T,hainiltoni M, freycineti N,ayraudi P,sexlineatus Cmacrocephalus V,phillipi U,carinirostris V,poeciloIaemus
5, A,tamarensis 57, U,tragula 34, M,elongatus 12, B,jacksonianus 3, A,australis 54, T,glaber 44, P,olorum 37, Canolius 51, S,argus 25, H,australis 48, S,lineolatus 30, M,strigatus
Figure 4.10: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in St Georges Basin. Data was 4* root fransformed. Stress = 0.17 133
M,freycineti M,trachylepis P,sexlineatus A.frenatus P,olorum A,tamarensis A,australis E,armatus Ctricuspidata Csubfasciatus D.punctulatus M,elongatus Csemivestitus A,jacksoniensis T,glaber P,signifer P,grandiceps R,macrostoma M.cephalus U,carinirostris P,saltator A,bifrenatus
M,chinensis Sphyraena spp A,viridis F,exquisites S,fuscescens A,elongata L,argentea L,genivittatus A,microstoma H,compressa A, striatus F.lateralis N,ayraudi T,hamiltoni Caustralis A,spilomelanurus B,kreffti P,lupus H,australis L,genivittatus V,poecilolaemus S,lineolatus V,phillipi A,reinhardtii R,sarba P,dentex S,neopilchardus Cmaculatus M,argenteus S,flavicauda H, vittatus Cauratus Meuschenia spp Philypnodon spp. S,nigra
Figure 4.11: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the enfrance, central and upper locations during each sampling event in Lake Conjola. Data was 4"" root transformed. Sfress = 0.17, 134
A,spilomelanurus F,commersonii P,dentex R, sarba F,exquisites H,compressa Meuschenia spp, Philypnodon spp, T,hamiltoni A,australis S,lineolatus F,lateralis A,bifrenatus Scarus spp. S.nigra' A,frrmamentum M,chinensis S,fuscescens P,lupus T,glaber A,elongata Caustralis V,phillipi A,frenatus M,argenteus S,argus V,poecilolaemus
A.reinhardtii A,microstoma H.vittatus M,elongatus E,armatus M,cephalus S,granulatus A,tamarensis L,argentea A.jacksoniensis P,saltator D,punctulatus A,viridis Csemivestitus Scorpis spp, M,freycineti H,aus trails Ctricuspidata P,signifer P, sexlineatus M.trachylepis P.grandiceps R,macrostoma U,carinirostiis
Figure 4.12: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Burrill Lake, Data was 4* root transformed. Stress = 0,16 135
P,jenynsii
A,microstoma F,lateralis F,exquisites A.reinhardtii A, tamarensis S, ciliata 3^3 J Philypnodon spp. M,elongatus A,elongata P,fuscus Csemivestitus P,signifer A,australis H,australis M,cephalus P,grandiceps A,bifrenatus P,olorum U,carinirostris
Caustralis A,viridis Caustralis Cholbrooki M,freyciniti L,argentea T,hamiltoni M,trachylepis B,kreffti V,poecilolaemus M,chinensis H.regularis Cgreyi A,frenatus S,flindersi P,arsius R,macrostoma R,calcaratus V,phillipi
Figure 4.13: Multi-dimensional scaling plot of species similarities, based on fish abundance data caught at the entrance, central and upper locations during each sampling event in Coila Lake, Data was 4* root transformed. Sfress = 0,14, 136
A,microstoma A,jacksoniensis Csemivestitus Canolius R,macrostoma A,tamarensis M,cephalus P,signifer Philypnodon spp. G.subfasciatus C.australis Cargyropleura M.trachylepis H,australis M,chinensis P,olorum E,australis A.frenatus A.reinhardtii M.freycineti ^ D.punctulatus P.sexlineatus Fs .elongatus A.australis L,argentea yioi5 3^ G.tricuspidata V.poecilolaemus U.carinirostris 45 42 F.lateralis S,arguoor^..^s V,phillipi A,viridis P,saltator A,elongata A,bifrenatus
D,lewini P, dentex T,glaber Microcanthidae B,kreffti spp. P,urvilli P,lupus T.hamiltoni S,fuscescens R,sarba N, ayraudi S,granulatus F, exquisites P,jenynsii M,argentus
Figure 4.14: Multi-dimensional scaling plot of species similarities, based on fish abimdance data caught at the entrance, central and upper locations during each sampling event in WaUaga Lake. Data was 4* root transformed. Sfress = 0,17, 137
For all estuaries, a large number of species were caught infrequently and in very low numbers.
This number of rarely caught species ranged from approximately 12 species in Coila Lake
(Figure 4.7), 18 species in Lake Illawarra (Figure 4,3), 19 species in Wallaga Lake (Figure
4.8), and 22 species in St Georges Basin and Lake Conjola (Figure 4.4, Figure 4.5). Most of these species were marine visitors or sttagglers, or species that were more commonly found in other habitats, such as sandy shallows. For some lakes, these "rare" species were highly influential on the pattems in fish assemblages. For example, in Lake Illawarra, of the eighteen species caught in low numbers, half were caught at the enttance site (Figure 4.3). The composition of these non-core species also changed between lakes. For example,
Vanacampus phillipi was caught in low abundance and sporadically in Lake Conjola (Figure
4.5), and not at all in Burrill Lake (Figure 4.6), but was part of the 'core' group of species in
Wallaga Lake (Figure 4.8) and St Georges Basin (Figure 4.4).
4.3.2.3 Patterns of species-association within individual ICOLLs
Within Wallaga Lake and Burrill Lake, the high degree of similarity in fish faunas between locations (Figure 4.1), was due to a high number of shared species between locations that were also captured consistently across sampling events (Figure 4.8 and Figure 4.6). Thus, there were a low number of species that were unique to just one location. Wallaga Lake had a particularly large 'core' group of species compared to the other lakes (Figure 4.8). This explains why the fish community at the enttance, centtal and upper location of Wallaga Lake were found to be highly similar in the MDS plot (Figure 4.1). There were 21 species that were caught consistently throughout the sampling period, and these included Amoya frenatus,
Meuschenia freycineti, Pelates sexlineatus, Acanthopagrus australis, Girella tricuspidata and 138
Urocampus carinirostris (Figure 4.8). Notably, there were no fish species in Wallaga Lake
that had a restricted distribution at one location, and so there were no characteristic species to
any region within this estuary. Those species that were only caught at one location were in
exttemely low numbers (e.g., only one or two individuals) and were caught during only one or
two sampling events. Examples of such species are Achoerodus viridis, Tetractenos glaber
and Tetractenos hamiltoni (Figure 4.8).
The situation was very similar for the fish assemblages of Burrill Lake, While Ambassis jacksoniensis was caught on the majority of occasions in high numbers, species such as
Meuschenia freycineti, Girella tricuspidata, and Pelates sexlineatus were a consistent feature
of the catch at each site within Burrill Lake, as were Meuschenia trachylepis, Philypnodon
grandiceps and Atherinosoma microstoma to a lesser extent (Figure 4.6). There were species
that were found across all localities within Burrill Lake, but were more prominent in the fish
community at the central and upper locations, such as Redigobius macrostoma, Urocampus
carinirostris and Gobiopterus semivestitus. Like Wallaga Lake, those species that were
caught in only one location in Burrill Lake were caught in low numbers and on very few
sampling occasions (Table 4.6).
Differences in the fish community structure between the entrance, centtal and upper locations
of Lake Illawarra, St Georges Basin and Lake Conjola were driven by two processes: species
caught at all locations within the lake, but whose numbers were highly variable; and the
absence of particular species at some locations. Also within these three estuaries there was
less consistency in the catch rates of species, across the three locations, and between sampling
events. In Lake Illawarra, the four most abundant species exhibited varying consistency in their catch among locations. For Atherinosoma microstoma and Afurcagobius tamarensis the 139
consistency of capture was less at the enttance and upper locations compared to the centtal site, while Gobiopterus semivestitus had significantly higher abundance and rate of capture at the central and upper locations (Figure 4.3). Species that added to the similarity between locations due to their capture at all locations, but in lower abundance and less consistently between sampling events included Acanthopagrus australis, Mugil cephalus, Redigobius macrostoma and Urocampus carinirostris. Species that added to the dissimilarity between sites were most noticeable for the enttance location, with Favonigobius lateralis, Petroscirtes lupus, Tetractenos glaber, Achoerodus viridis and three Syngnathidae species being caught more consistently at this location (Figure 4.3). At the centtal location there was only one species that was caught in higher abundance, Dicotylichthys punctulatus and at the upper location Psuedomugil signifer could be regarded as characteristic of this site (Figure 4.3).
Lake Illawarra and Lake Conjola had a similar core fish fauna, in terms of species diversity and composition (Figure 4.9 & 4.11). The separation of the Lake Conjola fish fauna was due to species that had preference for two of the three locations. Most of the core species were in higher abundance and more consistently caught at the centtal and upper locations. This included Gobiidae species, Ambassis jacksoniensis, Myxus elongatus and Gerres subfasciatus
(Figure 4.5). Similarity between the enttance and the centtal locations was due to the capture of Meuschenia freycineti, Meuschenia trachylepis and Pelates sexlineatus at these sites, while species such as Acanthopagrus australis and Girella tricuspidata were caught evenly across all locations (Figure 4.5).
St Georges Basin had a high species diversity but low total abundance of individuals (Table
4.1), and had one of the less diverse 'core' group of species (Figure 4.4). While, its 'core' group had a similar composition to the other estuaries, with the presence of Gobiidae species. 140
Monacanthidae, Ambassis jacksoniensis, Pelates sexlineatus and Girella tricuspidata (Figure
4.4), it was different in that three Syngnathidae species were a dominant feature of the fish fauna. Separation of the fish assemblage at the entrance, central and upper locations was due to Philypnodon grandiceps, Siganus fuscescens, Atherinosoma microstoma, Scobinichthys granulatus and Enoplosus armatus, which were caught at the enttance and centtal locations.
Species such as Nelusetta ayraudi and Scorpis lineolatus were caught only at the enttance location. The only species that exhibited a clear preference for the upper location in St
Georges Basin was a pipefish species, Stigmatopora argus (Figure 4.4).
4.3.3 Similarity of fish community structure on a regional scale
Hierarchical classification using the fish fauna composition at the three locations in the six estuaries indicated that the separation of the fish community of the six estuaries occurred mainly on the basis of estuary, that and location and time of sampling had only a secondary effect (Figure 4.15).
The ordination plot of the MDS clearly shows the separation of the Coila Lake samples from the other five estuaries (Figure 4.15). The Coila Lake samples cluster together as one large group, which indicates a low dissimilarity in the composition of fish faunas within this lake.
Within the large cluster of the other five lakes, the Wallaga Lake samples were placed very closely together in ordination space. For the remaining estuaries there was a separation of the enttance, centtal and upper locations for all lakes, indicating a slight and progressive change in fish community structure from the enttance to the upper region. Similarities in species composition are apparent between Lake Illawarra and Lake Conjola which were placed 141
B H
B H El % B ^t B B
Stress = .15
Symbol for estuaries • Lake Illawarra •Burrill Lake B St Georges Basin A Coila Lake • Lake Conjola • Wallaga Lake
Figure 4.15: Two-dimensional MDS plot of fish abundance data from the six estuaries, separated into locations and seasonal samples. Blue represents samples from the entrance location, orange the cenfral location and green the upper location. 142
closely together inordination space. Likewise, St Georges Basin and BurriU Lake showed a high degree of similarity in their fish faunas (Figure 4.15). However, aH five lakes show a high degree of similarity, and this emphasises that a number offish species are conmion to all estuaries, and that species composition is similar across the three locations within each lake.
However, estuaries could be delineated by differing abundances of shared species. In general, the typical "core" species were also the most abundant (Table 4.1). As a result, discriminating species were not informative, as the differences between estuaries were not based on species that were found only in certain estuaries along the coastline or restricted to an estuary, but rather on the differing abundance of catches of small, cryptic schooling species (Table 4.1).
By definition there were no restrictive species on a biogeographical scale. Similar to the individual estuary situation, species that were caught in only one estuary were those species that were caught sporadically in low abundance (typically single individuals), and were commonly marine sttagglers. There were also no 'restricted' species that had strong or distinct location-associations within estuaries. Rather species may have had preferences for certain regions but were not restricted to them. For example, Pseudomugil signifer was in high numbers and therefore appeared to prefer the upper locations of the ICOLLs, while
Favonigobius lateralis were more common at the enttance locations and preferred low seagrass densities.
Despite the sampling program covering a wide region of the southeast Australian coastline (~
400km), no biogeographical pattems were apparent in the classification and ordination procedures. The two estuaries that are situated in the southem most region of the state - Coila
Lake and Wallaga Lake - had little intemal differentiation in their fish assemblages but the 143
Table 4.1: Dominant, typical and discriminating species in communities defined by similarities of shallow water fish samples from NSW south coast estuaries. Dominant species ranked by total abundance with cut-off at ~80% of total untransformed (raw) abundance. Typical and discriminating species based on arbifraiy cut-off values of percentage similarity (>6% and 5% respectively) in SIMPER analysis
Estuary Dominant Total % Ab. Cum. Typical species Discriminating species Ab. of total % Ab. species Scientific name Common name
Lake A.mlcrostoma 6084 22,5 22,5 A.jacksoniensis Glassy perchlet BL; CL; WL Illawarra A.jacksoniensis 5746 21.3 43,8 G.tricupsidata Luderick (LI) P.signifer 3505 13.0 56.8 G.semivestitus Glass goby LC G.semivestitus 3349 12.4 69.2 A.mlcrostoma Small-mouth hardyhead BL; LC; SGB P.grandiceps 1440 5,3 74.5 A.australis Yellowfin bream A.tamarensis 1151 4,3 78.8 A.tamarensis Tamar river goby P.olorum 1093 4.0 82.8
St A.jacksoniensis 9082 61.2 61.2 A.jacksoniensis Glassy perchlet LC;CL Georges P.sexlineatus 1006 6.8 68 P.sexlineatus Eastem striped trumpeter Basin V.poecilolaemus 743 5.0 73 G.tricupsidata Luderick (SGB) G.tricupsidata 732 5.0 78 V.poecilolaemus Long-snout pipefish A.elongata 388 2.6 80.6 M.freycineti Six-spined leatherjacket
Lake G.semivestitus 13908 37.9 37.9 P.grandiceps Flatheaded gudgeon SGB Conjola A..jacksoniensis 6478 17.7 55.6 G.semivestitus Glass goby BL;CL;LI; SGB (LQ P.grandiceps 3445 9.4 65 A.tamarensis Tamar river goby P.signifer 3318 9.0 74 P.signifer Southem blue-eye BL; CL; LI; SGB A.tamarensis 1156 3.2 77.2 R.macrostoma 1057 2.9 80.1
Burrill A.jacksoniensls 14421 65.1 65.1 A.jacksoniensis Glassy perchlet LC; CL; LI Lake A.mlcrostoma 2493 11.3 76.4 G.tricupsidata Luderick (BL) M.cephalus 1551 7.0 83.4 P.sexlineatus Eastem striped trumpeter P.grandiceps Flatheaded gudgeon M.freycineti Six-spined leatherjacket
Coila A.mlcrostoma 29763 71.3 71.3 A.mlcrostoma Small-mouth hardyhead BL; LC; LI; Lake SGB; WL (CL) G.semivestitus 4609 11.0 82.3 Csemivestitus Glass goby LC F.exquisites Exquisite sand-goby BL U.carintrostis Hairy pipefish A.elongata Elongate hardyhead A.australis Yellowfin bream P.grandiceps Flatheaded gudgeon
Wallaga G.semivestitus 25997 42.3 42,3 G.semivestitus Glass goby BL; CL; LI; SBG Lake A.jacksoniensis 18081 29.4 71,7 A.jacksoniensis Glassy perchlet LC; CL; LI (WL) R.macrostoma 5758 9.36 81.06 R.macrostoma Large-mouth goby BL; LC; CL; LI; SGB P.olorum Blue-spot goby A.tamarensis Tamar river goby 144
assemblages were very different to each other (Figure 4.15). Also, while the samples from
Wallaga Lake cluster tightly together they were situated within a larger cluster containing samples from the other four estuaries. This indicated that the fish assemblages in Wallaga
Lake seagrass habitats were more similar to those in Lake Hlawarra, St Georges Basin, Lake
Conjola and Burrill Lake, rather than to the much closer to Coila Lake. There were some species that were noticeably absent or caught in very low numbers in some of the estuaries.
Acanthopagrus australis was caught in very low numbers in St Georges Basin and Burrill
Lake (see Table 3.2). Unlike most of the other estuaries, St Georges Basin also had low numbers of Atherinosoma microstoma, and Pseudomugil signifer or Gerres subfasciatus, a freshwater species and an estuarine spawning species respectively, were not caught in this estuary over the three-year period (see Table 3.2).
4.3.4 Evaluation of Rare species
This study involved an intensive sampling program covering a large spatial scale in which each ICOLL was sampled 144 times. As such, it provides a very interesting overview of rarity in the ICOLL fish assemblage of SE Austtalia.
Twenty-six species were common to all six estuaries, whereas thirty-one species were unique to one of the estuaries (see Table 3.2). St Georges Basin had the highest number of unique species (9), and Lake Illawarra the lowest (2 unique species) (Table 3.2). Fifteen species were caught on a single occasion and were represented by only one individual each, and a further twenty-seven species were caught in numbers of less than ten. When considered over a large spatial scale, these infrequently caught species were a feature of the fish assemblage. 145
There was little consistency in species occurrences among the seven estuaries, with many species abundant in some estuaries but rare in others. For example, for nine of the twenty most abundant species, over 50% of the total catch was from one estuary. 70% of the total catch of Atherinosoma microstoma was made from Coila Lake, and over half of the total catch
of Mugil cephalus was caught in Lake Conjola (Table 3.2). No species had more than 10% of their total catch from one estuary. Only three species, Afurcagobius tamarensis, Urocampus
carinirostris and Gobiopterus semivestitus were found with at least 50 individuals in all seven
estuaries. If species were found in all seven estuaries, the range of catches across the estuaries was usually high. For example, only three individuals of Vanacampus poecilolaemus were
caught in Coila Lake, but over a hundred in Lake Illawarra and up to seven hundred in St
Georges Basin (Table 3.2).
Using a criteria of low abundance in the catch (<5% of total catch, pooling 144 samples from
each estuary), there were many species absent or rare from one or two estuaries, but found in moderate to high numbers across the remaining estuaries. Twelve of the twenty most
abundant species were rare (<5%) or absent from at least three of the seven estuaries, highlighting the overall unevenness in the pattems of distribution and abundance for many species among the estuaries.
On another criteria of distribution and area of occupancy, 38 species could be considered rare in that they were caught at less than 10% of all sites (i.e.; at only one or two sites) (Table 3.2).
Gambusia holbrooki was excluded from this list as it is an inttoduced species, and were caught at only one site on one occasion (169 individuals in Coila Lake). Species caught at 146
Table 4.2 List of estuarine fish species considered rare, on the criteria of distribution and area of occupancy (<10% of all sites), from sampling of the estuaries studied.
Species Occurrence in this study Other habitats reported occurrence in Sardinops neopilchardus Lake Conjola (m) Adults coastal waters, juveniles estuaries Spratelloides robustus Merimbula Lake (e) Estuaries and coastal bays Engraulis australis Wallaga Lake (m & u) Coastal & ofiEshore waters, may enter large embayments Gonorynchus greyi Coila Lake (e) Sandy estuaries to deep offshore Cnidoglanis macrocephalus St Georges Basin (m) Rocky estuaries, sUty coastal bays Antennarius striatus Lake Conjola (e) Coastal bays, inshore reefe Tylosurus gavialoides St Georges Basin (u) Oceanic species, coastal reefs Strongylura leiura St Georges Basic (u) Oceanic species Sphyraena species Lake Conjola (m) Oceanic species Fistularia commersonii Lake Illawarra (e) Inshore to deep outer reef. Juveniles Burrill Lake (e) conunon in estuaries over mud. Hippocampus breviceps St Georges Basiu (m & u) Weed patches attached to sand, sargassum weeds. Hippocampus whitei St Georges Basin (m) Seagrass, kelp under jetties Syngnathoides biaculeatus Merimbula Lake (m & u) Seagrass beds or algal flats in lagoons & bays. Have been found in Sargassum rafts floating offshore Platycephalus fitscus Coila Lake (e) Sand habitat Dinolestes lewini Wallaga Lake (u) Shallow seagrass to deep ofishore reefs. Sillago flindersi Coila Lake (m & u) Sand habitat in estuaries, coastal bays Sillago maculata Lake Illawarra (e) Young seagrass and rocky estuaries, Coila Lake adults deeper coastal bays on sandy flats Lethrinus genivittatus St Georges Basin (e) Shallow coastal reefs & seagrass beds. Lake Conjola (e) Juveniles common in Sydney harbour & Botany bay Parupeneus signatus Lake Illawarra (e) Coastal reefs & estuaries Lake Merimbula (e) Lake Illawarra (e) Coastal reefs & lagoons Upeneus tragula St Georges Basin (e) Upeneus species Merimbula Lake (e) Coastal reefs & lagoons Upeneichthys species Merimbula Lake (e) Coastal reefs & lagoons A budefduf species St Georges Basin (u) Coastal reefs Sphyraena species Lake Conjola (m) Reefe &coastal bays Odax acroptilus St Georges Basin (e) Coastal to offshore reefs in kelp to 25m. Juveniles in seagrass in exposed coastal areas Scarus species BurriU Lake (e) Marine, reef species Pseudophritts urvillii Coila Lake (e) Marine, brackish & fi-eshwater Omobranchus anolius St Georges Basin (u) Distn. Gulf Carp. To Spencer Gulf. Wallaga Lake (u) Commonly observed in NSW estuaries with oyster shells. Port Phillip bay intertidal zone. Heteroclinus perspicillatus Merimbula Lake (m & u) Rockpools and intertidal areas Cristiceps argyropleura Wallaga Lake (u) Kelp beds to depths of 60m NSW to Bass strait Repomucenus calcaratus Coila Lake (e) Coastal bays on sand flats near reefs, 5- 100m depth. Galaxis maculatus Lake Conjola (m) Freshwater Pseudorhombus jenynsii Coila Lake (e) Sand Wallaga Lake (u) Arothron flrmamentum Lake Illawarra (e) Primarily pelagic {10-180m). also inshore Burrill Lake (m) on reefs.
References: (Thomson 1977; Hutchins & Swainston 1986; Allen & Swainston 1988; Kuiter 1993; McDowaH 1996, Pogonoski etal 2002) 147
10% or less of the sites also had low abundance, in most cases less than ten individuals (Table
3.2).
In order to consider the reliance of these 'rare' species on the seagrass habitats in ICOLLs, a table has been complied which attempts to summarise existing information on the distribution ofthese species in altemative habitats (Table 4.2). The majority ofthese species, identified as rare in ICOLL seagrass habitats, are more commonly found in other areas (Table 4.2). Most noticeably, these species are found in inshore coastal habitats, such as rocky reefs, or over sand habitat in estuaries (Table 4.2). There are also a number of species, from families such as Sphyraena and Microcanthidae that are marine species found in open ocean and/or coastal reefs. There were species that are found in estuaries at the juvenile stage, such as
Spratelloides robustus, Sardinops neoplichardus, Sillago flindersi and Sillago maculata.
These were all caught in low abundances, and it is highly likely that they utilise other habitats within estuaries, and hence would not be targeted by this sampling program. There were few species that could be considered to be rare, but which are only known to be associated with seagrass habitats. This includes the pipefish, Syngnathoides biaculeatus, which was only caught in Merimbula Lake (Table 4.2).
There were six other species that also had low abundances (less than 10 individuals), but were caught at a higher number of sites (between 5 and 7) (Figure 4.16). Many ofthese species are found in other habitats, such as over sand (e.g., Pseudorhombus jenynsii and Spratelloides robustus). The low numbers of Penicipelta vittiger caught during this study in only three
ICOLLs may be of some concem, as it is reportedly widespread from NSW to Westem
Austtalia (WA) and Tasmania (Kuiter 1993). Relatively little is known about the biology of this leatherjacket species and it has been reported inhabiting various habitats from seagrass 148
beds to outer reefs (Kuiter 1993). There were only two other species caught that could be considered to have both a low abundance and a low number of sites of occupancy in this study; Brachaluteres jacksoniensis and Sillago ciliata. Sillago ciliata is commonly found over sand, but Brachaluteres jacksonianus is reported to be found in shallow seagrass beds to
deeper weed habitats. It is widespread from southem Queensland to Westem Australia and
Tasmania, but it was only found at 4 sites with 13 individuals caught in this study.
A large number of species were caught from 10-90% of all sites (Figure 4.16). Eight species were considered to be core species, in that they were caught at 90% of the sites (i.e., at 20 or
21 sites) (Figure 4.16). Species that were caught at 20 of the 21 sites were Philypnodon grandiceps, Gobiopterus semivestitus, Redigobius macrostoma, Meuschenia freycineti and
Acanthopagrus australis. Three species were common to all sites; Girella tricuspidata,
Urocampus carinirostris and Afurgobius tamarensis.
25-,
20-
0) •3 15 • ^ 10 5- • i ^^gfl^ jg^g^l II. 1 IiI 1 I 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Sites occupied Figure 4.16: The number of fish species found with increasing number of sites. Sites include the entrance, central and upper locations of the seven estuaries. 149 4.4 Discussion While this study has been restricted to the use of one principal sampling method, that method is considered very effective for sampling shallow water habitats, and seine nets have been employed in many estuarine fish sampling programs (Pollard 1994a; Gray et al 1996; Hannan & Williams 1998). There have been some significant outcomes of this research. Firstly, it was found that location of sampling sometimes has an effect on fish community structure in ICOLLs, and this can be a result of several different processes. Year to year pattems dominate compositional change and were greater than season to season variability. Lastly, it is suggested that localised factors for particular ICOLLs are playing a significant role in the dynamics of fish community stmcture, rather than general geomorphology or biogeography. This study has shown that the fishes within the ICOLLs of the NSW south coast form moderately species-rich assemblages that were numerically dominated by a few taxa. The fish assemblage was comprised of many species that were rarely caught and in low numbers, as well as a few species caught in large numbers. This is a common characteristic for temperate and subtropical estuarine fish populations throughout the world (Whitfield 1989; Gaughan et al. 1990; Harrison & Whitfield 1990). The shallow water seagrass habitat supported juveniles of marine species that spawn in the ocean, and resident estuarine species that both utilise this protected habitat as a nursery ground. There is little life-history information for most of the south-eastem Australian estuarine fish fauna. Without this information it is difficult to separate the assemblages into the truly estuarine-dependent fish species from primarily marine migrant species. However, it was evident tiiat more than two-thirds of the fish assemblage was comprised of species that have marine affinities, and approximately a quarter of all 150 species being considered permanent estuarine residents. As expected, the freshwater component was relatively insignificant, with species considered to be primarily freshwater comprising only 5% of the overall number of species. 4.4.1 Fish Assemblages of SE Australian ICOLLs One of the striking results of this study was the similarity of fish assemblages within each estuary and among the estuaries. The ordination of the fish faunas showed that samples from different locations within each lake were more similar to each other than to representative areas in the other lakes. Ferrell et al (1993) found a similar situation for three estuaries along the central and southem coastline of NSW. For Lake Illawarra, St Georges Basin and Lake Conjola there was a slight differentiation in the fish assemblages from the enttance region, to those at both the central and upper sites to the entrance region (Figure 4.1). Thus, different regions of the estuary were characterised by slightly different faunal compositions. However, there were also large overlaps of "common" or "core" species. For example in Lake Illawarra, there were 28 species that were common to all three locations. For the remaining estuaries (Coila Lake, Burrill Lake and Wallaga Lake) ordination revealed a lack of discrimination into primary groups of sites from the three regions. For these three lakes, there was a high degree of similarity of fish assemblages caught at the entrance, centtal and upper locations, and the development of any distinct zonation pattem within these estuaries was not highly apparent. A compositional change in fish community stmcture with increasing distance from the estuary mouth has been documented for some other intermittently open systems, particularly for estuaries that are permanently open, such as coastal riverine systems (Bennett 1989; Whitfield et al 1989; Loneragan & Potter 1990; West & King 1996; Hannan & WilHams 1998). hi 151 many of these estuaries, this compositional change is the result of the presence of marine spawned recmits at enttance locations, and estuarine residents and freshwater species at the central and upper regions (West & King 1996; Hannan & Williams 1998). Slight differences in the community stmcture between the entrance, centtal and upper regions of Lake Illawarra, St Georges Basin and Lake Conjola were found in this study. However, the compositional changes were driven by different processes. It was differences in abundance of shared species, rather than presence/absence of species, that contributed most to the dissimilarity between communities within estuaries. There were essentially no species that were restricted or unique, or could be labelled as representative of a site. Species with restricted distributions did not contribute greatly to the dissimilarity of the fish fauna between locations within estuaries. While there were no distinct fish communities found at the enttance, central or upper regions, there were species that obviously preferred one of the locations and were more abundant at these locations. Over the entire study, no species was captured that could be regarded as having fidelity to a site or region within an estuary. It appears that juvenile fish species recmiting to these relatively small ICOLLs may only have fidelity to habitat stmcture, perhaps a result of the lack of variability in environmental conditions, particularly salinity between sites throughout these estuaries. Another process contributing to the small compositional change in fish assemblages between the enttance, centtal and upper regions of Lake Illawarra and Lake Conjola, were the numbers of infrequently caught marine visitors at the enttance, and the changing conditions of the enttance region within these ICOLLs. A high number of species classified as marine stragglers were caught sporadically and in low numbers at the enttance region of Lake Illawarra, and this added to the dissimilarity between the enttance samples to the centtal and 152 upper samples. The enttance region of Lake Conjola differed to the centtal and upper regions as a result of lower species diversity and abundance due to habitat loss from artificial manipulation of the enttance mouth. This artificial opening of the enttance caused major erosional damage to the dune areas around the mouth of the estuary and resulted in dramatic changes in water cfrculation and current strength. While this opening occurred in July 1998, during the remaining study period the seagrass beds at the enfrance did not fiilly recover. So despite the increased tidal inundation, the value of this site as a nursery area was lowered. 4.4.2 Seasonal and yearly variability in fish assemblages Marked seasonal changes in the stmcture offish communities in estuaries is a common feature of many studies, attributed primarily due to the spring/summer immigration of new recmits of marine species (Loneragan et al 1986; Bennett 1989; McNeill et al 1992). Fish larvae of marine and estuarine species in temperate and subtropical estuaries tend to peak in abundance in spring, summer and early autumn, and are least abundant in winter (Miskiewicz 1987; Whitfield 1989; Harrison & Whitfield 1990; Neira & Potter 1994; Gray «fe Miskiewicz 2000). However in this study, year to year variability was much greater than season to season variability. In the second year, high rainfall caused many of the ICOLLs to open for an extended period, leading to high abundances of many recmiting species (see Chapter 5). In the third year, there was a noticeable decrease in species diversity and abundance for many of the ICOLLs. In addition, a common feature of these ICOLLs was the large numbers of 'core' species that were caught quite consistently, both seasonally and at most locations, and thus causing similarity in the fish assemblages throughout the year. As a result, overall differences 153 between years were very noticeable in the fish assemblages, and this was largely driven by large differences in abundance of particular species between years. Only weak seasonal differences in fish community pattems were detected in this study and temporal change in the assemblage composition was poorly associated with seasons. Most estuaries displayed significant differences in species diversity and abundance due to the factor of sampling event (see Chapter 3). However, and quite surprisingly, it was common for the spring, summer and autumn samples to all contain new recmits, adding to overall similarity between seasons. In most cases it was only the winter samples that displayed significantly lower abundance and diversity, and these became the outliers in the MDS ordination plots (Figure 4.2), Bennett (1989) found that for the Bot Estuary (southem Afiica) there were no marked seasonal changes, a feature he related to the entrance being closed to the sea. He found that in the permanently open Palmert Estuary (southem Afiica) winter samples separated from the spring/summer samples due to the immigration of new 0+ recmits of marine species, whereas in the seasonally open and closed Kleinmond Estuary (southem Africa) seasonal changes were related to the efflux of marine migrants (Bennett 1989). The situation in the ICOLLs of SE Australia was not as consistent. Winters samples did separate in the permanently open Lake Illawarra, but not in the open St Georges Basin. In the closed Coila Lake, the fish community showed no marked seasonal effect in the first year; a situation similar for some other closed systems (Bennett 1989). The second and third year samples did show some seasonal separation due to species diversity increasing with the immigration of marine spawning recmits after the enttance opened (see Chapter 3), but yearly changes were more noticeable than seasonal changes. Surprisingly, seasonal pattems were not 154 detected in Wallaga Lake, which was intermittently closed and open, with only the winter sample from the third year separating out from the rest of the sampling events (Figure 4.1). 4.4.3 Influence of ICOLL morphology and hydrology on fish community structure In this study, it is apparent that the characteristic morphology and hydrology of the estuaries, and the regional climate, played major roles in stracturing the fish assemblages ofthese NSW south coast ICOLLs. These intermittently closed and open estuaries are quite small compared to other coastal water bodies, such as coastal rivers, and have limited freshwater inputs and tidal flows. The climate of the region is characterised by a lack of seasonal rainfall pattem. Evidence from North American estuaries suggest that the distribution of fish assemblages is often sttongly influenced by variations in salinity due to freshwater flows (Bottom & Jones 1992). In the intermittently open Chautengo Lagoon in Mexico, a pronounced pattem of seasonal rainfall resulting in large seasonal fluctuations in salinity, from freshwater to hypersaline conditions, was found to effect the relative composition of the fish fauna (Yanez-Arancibia 1985). Seasonal ttopical rainfall resulted in the opening of the Chautengo Lagoon on a predictable seasonal basis. This is also the situation in south-westem Austtalia where seasonal rainfall pattems affect salinity, and thus the stracturing of the fish communities (Loneragan & Potter 1990; Young et al. 1997). However in southem NSW, the lack of strongly developed seasonal rainfall pattems and the low volume of rainwater (Roy 1984), results in a haphazard opening regime for the estuaries, and there is less effect on salinity than other studied systems. 155 In many types of estuaries, the presence of a longitudinal salinity profile acts as a barrier to ocean-spawning species, and as a result euryhaline species are often distributed throughout the main body of the estuaries (Bennett 1989; Loneragan & Potter 1990; Hannan & Williams 1998). In the present study, the occurrence of particular ocean-spawning species at the entrance, centtal and upper locations within these ICOLLs would appear to be related to the lack of a horizontal salinity variation. Stenohaline species are able to penettate and survive away from the entrance region. Loneragan et al (1989) proposed that the penettation of marine-estuarine opportunistic species into the middle region of the Swan estuary was presumably related to the continual presence of high salinities. However, Haiman & Williams (1998) in a study of the marine-dominated Lake Macquarie of NSW, found there was a decrease in ocean-spawned individuals away from the entrance region, even though a salinity gradient did not exist. In the present study though, it was not uncommon for ocean-spawned individuals to be caught at the centtal and upper locations, with overall similar size ranges were found at all locations. The abundance and distribution of species considered to be ocean-spawned differed between estuaries. For example, Pomatomus saltator, which was found in highest abundance at sites fiirthest from the enttance of Lake Illawarra and Wallaga Lake. Such discontinuity in distribution and abundance was also found for other ocean-spawning individuals such as Meuschenia trachylepis. The highest catches of this species was at the enfrance of St Georges Basin but in Lake Conjola, Lake Illawarra and Burrill Lake, the cenfral locations had the highest numbers. In Wallaga Lake Pomatomus saltator was found at the upper location. There is evidence to suggest that some species are particularly suited to the habitat of intermittently opened lakes, such as the sparid Acanthopagrus australis and the muglids Myxus elongatus and Mugil 156 cephalus (Blaber 1987; Pollard 1994a). Other research in estuaries has concluded density- based intrasion of marine water, weak tidal action, and restricted or wind-driven circulation were insufficient to transport larvae far from the enttance region (Spencer 1959; Jenkins et al. 1996; Harman & Williams 1998). For the ICOLLs studied here, water ttansport, either induced from wind-driven circulation or ebb currents, may be sufficient to transport larvae away from the enttance, and the lack of environmental variability throughout the estuaries, particularly with respect to salinity, enabled these fish to establish widely. It is difficult to explore these questions as so little data exists for currents and water movements, for the majority ofthese ICOLLs (but see Chapter 6). It was also apparent throughout this study that localised factors and processes were important in stracturing fish communities. While the composition of the fish assemblages at each location and among estuaries was similar, many species exhibited a high degree of patchiness. There were many species that were notably absent or present in some estuaries. It was quite common for many species to be absent or rare (<5% of total catch) from one or two estuaries, but caught in similar numbers across the remaining estuaries. Even for the most abundant species, there was patchiness in catches within individual estuaries and many were rare or absent from at least three of the six estuaries. Only three species were caught in numbers greater than 50 individuals caught in all six esttiaries. Such pattems have been reported elsewhere for seagrass-associated fishes (McNeill et al 1992; Ferrell et al 1993). Possible factors for such pattems could be variation in habitat stractural complexity or a result of sampling efficiency due to certain fish behaviours. It is unlikely that variation in seagrass beds would explain the pattems observed here, as variation in seagrass stracture within and between zones have been found not to sttongly influence fish distribution (Bell & Westoby 157 1986b; Bell et al 1987; Bell et al 1988). Certain behaviours of fish such as schooling could have contributed to the patchiness in numbers. This was quite evident for Mullidae species in Burrill Lake and Lake Conjola. For some estuaries and localities there may be particular intrinsic environmental characteristics that effect recmitment and distribution of species. Oceanographic processes, such as exposure to currents or position of bed may concenfrate and maintain larvae in a certain area (McNeill et al 1992). It has been found that differences in shape of estuaries could affect the influence of distance from the mouth on fish recraiting to seagrass, and thus zone effects are likely to vary among estuaries (Bell et al 1988). Therefore the particular factors operating at a local level, such as the size and shape of the ICOLLS, few freshwater flows and water currents within ICOLLs in southeast NSW, are considered major contributors to pattems in the concentrations of fish larvae throughout the estuary. These ideas are ftirther investigated in Chapter 6. 4.4.4 Evaluation of conservation status There were no species that could be definitively listed as rare, on the basis of low abundance and/or area of occupancy. However, several species warrant fiirther attention in terms of rarity. These include the pipefish, S. biaculeatus, and the leatherjacket species, P. vittiger and B. jacksonianus. S. biaculeatus is listed as Data Deficient on the 2000 lUCN Red List of Threatened Species (Pogonoski et al 2002). Indeed all syngnathids are subject to the export confrols of the Commonwealth Wildlife Protection (Regulation of Exports and Imports) Act 1982 from r^ January 1998, and syngnathids and solenostomids are listed as marine species under s248 of the EPBC Act 1999. For S. biaculeatus there appears to be no evidence for decline of the species, as it has a wide distribution and its populations appear to be reasonably 158 secure in the wild. However, it is used in the Chinese traditional medicine frade and may be under increasing threat in this regard (Pogonoski et al. 2002). It is interesting to note that while all syngnathids are protected, several of the pipefish species caught in this study were actually some of the most common species. For example, Urocampus carinirostris was one of only three species that had abundances found in this study of at least 50 individuals in aU six estuaries. Judgements of the rarity status and vulnerability of the leatherjacket species is more difficult. There has been little scientific research of the life history and habitat usage of this group of fishes. There is reason for concem though as the leatherjacket fishery has largely declined in NSW waters and there is no clear identification of what species are commercially harvested. This makes informed judgements on the conservation status of particular leatherjacket species virtually impossible. It is very difficult to determine if a species is rare; that is, whether it has a naturally occurring small population and/or a narrow range, or whether it requires special management. For fish species, this is exacerbated by the particular life history characteristics of many marine populations. Fish population dynamics are characterised by varied and often unpredictable recmitment, with many sources of variation causing considerable short- and long-term turnover of species at any particular location (Houde 1987; Doherty & Williams 1988; Booth & Brosnan 1994; Caley et al 1996). Most marine and estuarine fish populations have distinct life history stages with a planktonic larval stage, juvenile and adult stage, which often utilise different habitats and regions. Thus the timing of sampling (within year and between) and the part of the life cycle that is targeted by sampling, will yield different results on abimdance and perceived rarity. Any determination of rarity for marine and estuarine fish populations must take into account temporal and spatial variability in populations and should consider the 159 different stages of life history. Recmitment dynamics are particularly variable, with the recmitment of marine larval fish has been documented to exhibit great variability at several spatial and temporal scales (Jones 1990; Steffe 1991; McNeiH et al 1992; Doherty & Fowler 1994; Levin et al. 1997) (see Chapter 5). Such variability demonstrates the need for a great deal of information about the ecology of fish species and highlights the need for long-term data sets. In reality, information for many Austtalian marine and estuarine fish species, particularly those of low economic importance, is poor and often restricted to presence/absence data. Range is another determinant used for consideration of rarity, and it is generally acknowledged that a species with a narrow or restricted range is more likely to be classified as rare (Rabinowitz 1981). For marine and estuarine fish species, range is likely to be on a biogeographic scale and it is unlikely for many species to exhibit a narrow or restricted geographic range. What is more likely to be more restricted is the habitat used for a certain part of the life cycle, such as spawning grounds and/or nursery areas. For example, the only confirmed spawning ground for Pomatomus saltator in Austtalia is located near Eraser Island, Queensland (Kailola et al 1993). Thus, while many marine fish species have large biogeographic ranges they still may be vulnerable to extinction if a particular aspect of their life history occurs within a narrow range. If a stage of their life history occurs in a narrow range then this could be considered to conform to some concept of rarity, even if the species has a large extent of occurrence. Thus, differentiation into stage of life history, habitat use and location may be a more usefiil indicator of the relationship between a species range and rarity for marine and estuarine fish populations. 160 While only the issue of rarity has been discussed here, there are also issues relating to threatened species. Threatened species may be at risk due to a threatening process, such as from fishery activities, and loss of a critical habitat. With a lack of detailed biological information of the majority of Australia's temperate inshore marine and estuarine species, it is difficult to make decisions on critical habitats, threatening processes, and what conservation and recovery actions will be needed. 4.4.5 Geographic patterns Surprisingly, despite this study being carried out over a very large spatial range, there were no major differences in species compositions over a wide geographic scale, which may have been expected due to a range of environmental and climatic variables in the region. Assemblages in the estuaries in the far south of the state did not differ markedly from those nearly 400km north. This was particularly evident in the data collected for Lake Illawarra, St Georges Basin, Lake Conjola, Burrill Lake and Wallaga Lake. Such a lack of pattem in fish communities over a wide spatial scale was also found by Gray et al. (1996) in estuaries of northem NSW. In fact, many species found in far northem NSW (Gray et al. 1996) were also found in this study of southem NSW. One reason for the lack of pattem may be the influence of the East Australian Current, which runs parallel to the coastline and is responsible for a high degree of ttansport and mixing along the coast and between estuaries (Miskiewicz 1987; Gray 1993; Smith 1999; Gray & Miskiewicz 2000). Thus, while the overall species composition of the estuaries was similar, there were differences in pattems of diversity and abundance on a local scale. As the esmaries investigated spanned across several spatial scales, from those several hundred kilometres apart 161 to tens of kilomettes, these local differences in fish assemblages are not explained by latitudinal or other large-scale spatial effects. Differences between species composition of estuaries may be related to species-specific responses to various physical and ecological factors due to particular morphology of an estuary, and the scale over which processes such as competition and predation act on newly-settled individuals must be local (Fowler et al. 1992). The only notable pattem of community change on a bioregional scale occurred during October 1998 when increased recmitment was evident across all estuaries and in July 2000, where all estuaries experienced a substantial decrease in numbers of fish caught and species diversity. Even though it is common for samples taken in the winter period to be low in numbers and diversity (McNeill et al 1992), the July 2000 period was dramatically lower to previous samples taken during winter. Such a dramatic decrease in species diversity and abundance across such a wide spatial scale could be related to a widespread failure in recmitment of many species during the year, and/or due to a result of food web interactions. For example, the major increase in the recmitment of large sized species may have impacted on the other smaUer sized fish species (e.g., hardyheads, perchlets and gobies) that are food items. This again highlights the need for long-term sampling and monitoring programs to detect such fluctuations in fish populations and to understand ecosystem interactions. In this region, such information is pertinent given the current management decisions involving these estuaries, such as decisions to artificial open enttances on an ad-hoc basis; constraction of permanent training walls; and the proposal to re-stock these estuaries with commercially and recreationally significant fish species. Significantly, estuarine environments are known to undergo numerous small successional changes directed by episodic events and hence rarely achieve a typical or stable state (Whitfield & Braton 1989). 162 Overall, these sources of temporal variability make it difficult to determine what the "typical" estuarine fish community is for the NSW south coast. This situation is confounded by the high variability in diversity and abundance pattems that was found within and between ICOLLs in this study (Chapter 3). However, this study also demonstrates the need of spatially broad, long-term ecological studies to incorporate and measure variability. These types of studies are essential to build the baseline data necessary to determine the extent of anthropogenic effects on the natural fiinctioning ofthese estuarine environments and their fish communities. 4.4.6 Effects of Opening and Closing The effects of opening an estuary on flora and fauna have been poorly investigated for the estuarine ecosystems in NSW. However, research on the Bot River estuary. South Afiica, has shown that the rapid changes in water-level and considerable changes in salinity have major consequences for the ecology of this system. While invertebrates, meiofauna, zooplankton and avifauna are negatively affected by artificial manipulation of the entrance condition (Heyl & Currie 1985; Bally 1987), it was found that the ichthyofauna is either little affected or positively affected by the opening (Bennett et al 1985). The most obvious benefit for the fish fauna of coimection to the ocean is that it allows recmitment of marine spawned larvae into important nursery areas, and the migration of adult fish trapped in the ICOLL to ocean spawning locations. In this study the effect of artificial opening of the enfrance mouth was most noticeable in Coila Lake, which was closed to the ocean for the first year of sampling. For this lake, tiiere appeared to be little influence on total fish numbers from the opening of the enttance during the second year, but the stracture of the 163 fish commimity did change substantially. As expected, the opening allowed the inttoduction of juveniles from ocean spawning species into the system. The entrance mouth only remained open for a matter of weeks, but as has been found with ICOLLs elsewhere, only a relatively short open phase is necessary to introduce new recraits (Whitfield 1998). The majority of these recraiting species were also of economic significance to fisheries and their presence in Coila Lake is obviously seen as favourable by recreational and commercial fisheries. However, artificially opening an estuary may also have indirect negative consequences for fish populations, particularly the potential of the estuary as a nursery site, and on the ttophic stracture of the estuarine ecosystem. It was estimated that for the Bot River estuary the resultant loss of water from breaching of the enttance dune barrier left large areas of seagrass beds exposed and as a consequence 90% of the aquatic macrophytes died (Bally et al. 1985). As a direct result, the associated commimities that rely on seagrass beds, such as juvenile fish, invertebrates and birds were adversely affected. Such damage to seagrass beds was recorded during this study at Lake Conjola, after its enttance was artificially opened in July 1998. Large, healthy seagrass beds are located at the enttance and provide habitat for a wide range of fishes in this lake (see Chapter 3). Entrance works conducted in the second year of this study caused a substantial increase in tidal and current movement, change in water levels and a resulting loss in seagrass beds at the enttance site (pers. obs.). This coincided with a large decrease in the number of individuals caught at this enttance site, which is commonly regarded as an important recmitment area, and as a result there are likely to be long-term consequences on the fish catches in this lake. For long- term management of fisheries the natural opening regime may prove more sustainable. 164 In regards to the management ofthese ICOLLs, the focus should move away from increasing fish and prawn recmitment, and investigate the long-term ecological consequences of manipulating the natural cycle of entrance openings of these estuaries. In South African intermittently open estuaries, it has been reported that food sources such as zooplankton and zoobenthos are higher in abundance when the estuaries are closed, and that when these estuaries are breached the available habitat and food sources are drastically reduced due to the loss of plankton and prolonged exposure of the benthos (Whitfield 1980; Blaber et al. 1984). If there are detrimental effects to species such as zooplankton and other important food sources, then resultant food web impacts on the fish populations are likely to be high, and competition among fishes for habitat and food would increase. Also, any loss of seagrass beds will have important consequences for estuarine fimction, particularly primary productivity. These ecosystem-wide issues should be considered carefiilly when decisions are made involving the health of the ICOLLs of southem NSW. 4.4.7 Conservation and management implications This study has shown that the ICOLLs of the NSW south coast support a relatively diverse fish community. The pattems offish community stracture found in this study suggest that the whole perimeter of the estuaries support juveniles of marine species that spawn in the ocean, and resident estuarine species that utilise this protected habitat as a nursery ground. While the importance of intermittently open systems in supporting estuarine-dependent marine fish stocks has been questioned (Pollard 1994a; Pease 1999), this study has shown that the ICOLLs are significant nursery habitats in this region. Also, unlike the coastiine of Westem Ausfralia where habitats such as fringing limestone reefs and protected rocky headlands offer 165 extensive altemative protected nursery habitats (Potter & Hyndes 1999), along the south coast of NSW, particularly in the far south, there are few altemate nursery areas. This unplies that the degradation of ICOLLs in this region would have a significant effect on local fish communities and coastal fisheries. Several findings of this study highlight that the protection of ICOLLs may require a different conservation sfrategy than that applied to other types of estuaries. There was a distinct lack of consistency in pattems of diversity and abundance, and sites of consistent recmitment, not only within the estuaries in space and time, but also these pattems were not consistent among estuaries. The implication for the conservation management of ICOLLs is that there is great difficulty in choosing an area or site with consistently high diversity and abundance, which is also representative of the whole range of fish species and ecological processes of an ICOLL. Furthermore, if management decisions are to be influenced by "unique" species then each of these estuaries could be considered as having some unique property and thus worthy of conservation. Each estuary supported a number of species that were only found in that estuary and many species had total numbers less than ten over the three-year study period. Some species were also noticeably present or absent in particular estuaries. The presence of new recraits around the whole perimeter of the estuaries was also another interesting find. Recent literature has tended to emphasize the value of the enttance as a nursery ground and hence this region should receive the greatest amount of protection (Hannan & Williams 1998). This study has shown that conservation management of ICOLLs would need to go beyond the reservation of the enttance region as a core sanctuary zone, and recognise that within an estuary many seagrass beds are required for the comprehensive protection of all species, 166 especially considering it is impossible to determine important recmitment areas from year to year within an estuary, and also between estuaries. Another fmding from the present study that has relevance to marine reserve selection was the low incidence of species that could be considered rare. The difficulties encountered when applying in-depth analysis of rarity was closely linked to the lack of biological knowledge for the majority of species. Nevertheless, it appeared that there were no species that could be considered rare, even though there was concem raised for the vulnerability of some species. There are many criteria suggested for selecting marine protected areas (Kelleher & Kenchington 1992; Agardy 1994; Kenchington & Bleakley 1994), and these may include such factors as high biological productivity, species richness, endemic or rare species, spawning and nursery areas, and important migratory pathways (Margules & Nicholls 1988; Norse 1993). One of the most commonly used approaches for the selection of reserves is the use of species diversity and the presence of rare species (Prendergast et al 1993). However, identifying highly biologically diverse areas known as "hotspots" (e.g., Wilson 1994), or the presence or rare species may not be the most usefiil basis for establishing a reserve network (Prendergast et al 1993), especially for ICOLLs in southem NSW. Studies have shown that simply counting the number of species in an area can be misleading and the occurrence of many rare species does not necessarily coincide with highly diverse areas (Margules & Nicholls 1988; Prendergast et al 1993; Wilson 1994). This sttidy has demonstrated that the use of a rarity criteria based on these shallow water seagrass fish communities, would be very misleading. The species that appear to fit the rarity criteria were often not actually dependent on seagrass beds or estuaries for their survival. Notably, community information on the 167 assemblage of organisms that co-occur in a habitat is seen as more valuable data, rather than a number of species present. 168 Chapter Five Spatio-temporal variation in the recruitment of major commercial fish species to SE Australian ICOLLs. 5.1 Introduction The abundance and diversity of the shallow-water seagrass fish communities of ICOLLs along a large section of the SE Austtalian coastline has been discussed in Chapter Three, and pattems in assemblages were discussed in Chapter Four. In this chapter, pattems of recmitment timing and sfrength for a number of specific species that are exploited by commercial and recreational fisheries will be investigated. In this chapter recmitment refers to the addition of the young-of-the-year individuals from the pelagic habitat measured at some arbifrary time after larval settlement (Connell 1985). Various aspects of the recmitment pattems of a number of fish species in Austtalian esmaries have been previously investigated (Loneragan et al. 1986; Bell & Pollard 1989; Warburton & Blaber 1992; Laegdsgaard & Johnson 1995), but there are few studies documenting the importance and utilisation of the estuaries south of the Sydney region by fish species harvested by commercial and recreational fisheries. The estuaries in south-east Austtalia are subject to a high degree of recreational fishing pressure, and depending on local regulation to varying degrees of commercial fishing. For example, for the past century, Lake Illawarra and St Georges Basin have been among the top 20 estuaries for commercial landings of species (e.g., Acanthopagrus australis and Girella tricuspidata) (Gibbs 1997). On the other hand, no commercial fishing is allowed in Merimbula Lake (Fletcher & McVea 2000). Despite this 169 high rate of harvesting, there is surprisingly little information on recmitment processes of these commercial species. Nor is there any information on the possible use of the shallow water seagrass habitat throughout these estuaries as nursery areas. In other regions, seagrass beds in the nearshore waters of estuaries constitute important nursery areas for recraits of a number of marine teleosts and euryhaline species (Bell & Pollard 1989; Connolly 1994). Several studies have suggested that recmitment of marine larval fish is highly variable at several spatial and temporal scales (Doherty & WilHams 1988; Jones 1990; Steffe 1991; Fowler et al 1992; McNeill et al 1992b; Booth & Brosnan 1994; Doherty & Fowler 1994; Levin et al. 1997). In south-east Australian estuaries, recmits of a number of specific species, such as Acanthopagrus australis, Rhabdosargus sarba, Girella tricuspidata and Monacanthidae species, settle in seagrass meadows such as Zostera capricomi (Middleton et al 1984; FerreH 8c Bell 1991; Steffe 1991). The peak recraitment time is often during the spring/summer period from August to December (Bell et al. 1988; McNeill et al 1992b; Worthington et al 1992a). However, spatial variation in recraitment of a number of species has been documented, such as differences between estuaries (McNeill et al. 1992b; Gray et al 1996) and among seagrass beds within estuaries (Bell et al 1988; McNeill et al 1992b; Worthington et al 1992a). On a temporal scale, large differences in the abundance of new recraits have been found between areas of similar habitat (Caffey 1985; Gaines & Roughgarden 1985) (see Chapter 3). The recraitment of fish populations is also known to be subject to high variability from year to year at the same location (Fowler 1990; McNeill et al 1992a), and some species are characterised by episodic recraitment events (Levin et al. 1997; Morison et al. 1998). There is some evidence to suggest that particular sites may receive a high abundance of recruits consistently, usually as a result of small-scale hydrological features 170 and oceanographic processes concenttating larvae into an area (Kingsford et al 1991; McNeill et al 1992b; Kingsford & Suthers 1994). This chapter has the objective of investigating the spatial and temporal variability in the recraitment of fish species of economic significance in the ICOLLs of SE Ausfralia. For the ICOLLs in SE Ausfralia, spatial variation in recraitment may also occur due to the intermittent closures of the entrance mouth, low tidal range and nearshore oceanic processes of the NSW south coast. These physical factors could lead to low levels of recraitment and/or greater spatial and temporal variability in recraitment to these estuarine habitats. For example, research on ICOLLs in southem Africa and Westem Australia have shown that the opening and closing regime has a direct impact on the fish communities, especially the recraitment of marine spawning species (Potter et al 1983; Bennett et al 1985; Blaber 1987). In SE Ausfralia timing of recraitment events will also be influenced by the East Ausfralian Current (EAC), which is the major current running parallel to the east Ausfralian coast, and represents a supply of larvae of many species (Miskiewicz 1987; Gray 1993). The EAC, local winds and coastally frapped waves drive circulation over the inner shelf (Nilsson & Cresswell 1980; Middleton et al 1997). These processes result in spatial and temporal variation in the distribution of larval fish in coastal waters, which may lead to variable recraitment of juveniles into estuaries (Gray & Miskiewicz 2000). As the EAC fravels south of the Sydney region, there are episodes of sfrong southwards flowing currents associated with the seasonal presence of warm-core eddies and small cyclonic eddies; these processes can cause both onshore and offshore current flows (Huyer et al. 1988). Despite the available information on recraitment of juvenile fish in the Sydney region, little is known of the sttength and timing of fish recraitment into ICOLLs in SE Austtalia. 171 Settlement and recraitment is a major part of the life history of fishes affectmg population size. An understanding of the spatial and temporal pattems and variability of recraitment is important for effective management of fisheries. There are very few studies for which a comprehensive analysis of recraitment over numerous spatial scales and across a number of years exists. An example is Gray et al. (1996), who studied eight estuaries in northem NSW; however in that study only the entrance sites were sampled. In this Chapter, large-scale (>500km) spatial and temporal pattems in the recraitment of juvenile fish have been examined for the seven coastal lakes in SE Austtalia over a three year period. The sampling program was designed to examine recraitment pattems for several sites located within these estuaries. Five species; Acanthopagrus australis (yellowfin bream), Girella tricuspidata (luderick), Meuschenia trachylepis (yellow-finned leatherjacket), Monacanthus chinensis (fan-belly leatherjacket) and Gerres subfasciatus (silver biddy), have been selected for detailed analyses. These species were chosen because they were relatively abundant in the estuaries studied. More importantly, though, there is a lack of life history information on these species, they are exploited by commercial and recreational fisheries, and the status of the populations is of concem. Background information on previously recorded recraitment times for these species is discussed in the results section, but this study represents the first investigation of recraitment for these species along the south and far south coast of NSW. 172 5.2 Methods 5.2.1 Field Sampling The data used for this chapter was collected as part of the sampling program described in Chapter Three. Recraitment information for selected species captured in the seven estuaries is included in this chapter for analysis. These estuaries are Lake Illawarra, St Georges Basin, Lake Conjola, Burrill Lake, Coila Lake, Wallaga Lake and Merimbula Lake. Field sampling methods have been described previously (Chapter 3) 5.2.2 Data Analysis The spatial and temporal variation in commercial fish species diversity and number of individuals within each individual estuary was assessed by using Analysis of Variance (ANOVA). The quarterly samples (Sampling Event) were regarded as a random factor in the model. Location within estuary was considered a fixed factor, as they were chosen as representative of distinct regions of the estuary; the entrance, centtal and upper. Abimdance data displayed heterogeneity and were ttansformed using logio(x+l), prior to analyses. In some cases this fransformation did not produce homogeneous variances, but ANOVA was used regardless as it is considered quite robust to departures of variances when sampling sizes are equal (Underwood 1981). To compensate for the increased likelihood of Type 1 error, a was set to 0.01. Where ANOVA indicated significant differences among means, these differences were examined with the Student-Newman-Keuls (SNK) test. 173 The relative contribution of each factor to the total variance in the ANOVA model was also investigated. These contributions were isolated from the mean-square estimates and expressed as proportions of the sum of all variances. 5.3 Results 5.3.1 General Summary A total of 16 617 fish were caught that were regarded to be of commercial and/or recreational importance (see Table 3.2, Chapter 3). Fish species were classified as commercial species on the basis of the NSW commercial fishing statistics, and with reference to selected reports (Kailola et al 1993; Kuiter 1993; Pollard 1994a). There were 37 species belonging to 20 families that were regarded as harvested by commercial and recreational fisheries (see Chapter 3 for fiill species list). In terms of species diversity, Coila Lake had the lowest number of commercial fish species (17 species), while similar numbers of commercial species, between 20-24 species, were found across the other six estuaries. The highest abundances of commercial species were caught in Lake Conjola. Lake Illawarra, Burrill Lake, St Georges Basin and Wallaga Lake had similar numbers of commercial fish caught, between approximately 2000-3000 individuals, while for Coila Lake and Merimbula Lake only 1689 and 1237 individuals of commercial significance were caught (Figure 5.1). Burrill Lake also had quite low catches of 174 commercial fish species caught on most occasions, but overall abundance was high as a result of a single large catch of Mugil cephalus during October 1998 (Table 5.1, Figure 5.1). Numbers of commercial species differed among estuaries, as did abundances of commercial species contributing to the total catch. The eight most abundant commercial fish species that were caught in each estuary are listed in Table 5.1. Similar species contributed to the 2000. Merimbula Lake 1000. 0. 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 ' 2000. Wallaga Lake 1000. 0.I I "P 10/97 2/98 4/98 7/9m8 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2000 Coila Lake 1000 0 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2000 BurriU Lake 1000. 0 1^ 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2000. Lake Conjola 1000. 0. ^—1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2000 St Georges Basin 1000 0. I I I I I •F"—p- 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2000 Lake Illawarra 1000. 0. ^•^^^^ I I I 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Figure 5.1: Total number of individuals considered important to commercial and/or recreational fisheries, caught during each sampling event within the seven estuaries. Locations have been pooled. Merimbula Lake sampled for two years only 175 Table 5.1: The 8 most abundant fish species (ranked), considered important to commercial and/or recreational fisheries, caught in the seven estuaries over the three-year sampling period. Estuary Species Abundance Lake Illawarra Girella tricuspidata 614 Acanthopagrus australis 537 Gerres subfasciatus 468 Meuschenia trachylepis 205 Pomatomus saltator 157 Mugil cephalus 157 Meuschenia freycineti 155 Achoerodus viridis 115 St Georges Basin Girella tricuspidata 732 Meuschenia trachylepis 339 Myxus elongatus 260 Mugil cephalus 146 Pomatomus saltator 135 Meuschenia freycineti 117 Monacanthus chinensis 78 Scorpis lineolatus 65 Lake Conjola Myxus elongatus 880 Girella tricuspidata 529 Acanthopagrus australis 481 Pomatomus saltator 369 Liza argentea 363 Meuschenia trachylepis 288 Mugil cephalus 246 Meuschenia freycineti 211 Burrill Lake Mugil cephalus 1551 Girella tricuspidata 365 Meuschenia trachylepis 144 Myxus elongatus 126 Meuschenia trachylepis 110 Acanthopagrus australis 43 Pomatomus saltator 28 Monodactylus argenteus 22 Coila Lake Acanthopagrus australis 811 Myxus elongatus 427 Hyporhamphus spp. 359 Achoerodus viridis 35 Girella trlcupsidata 21 Sillago ciliata 10 Sillago flindersi 8 Meuschenia freycineti 5 Wallaga Lake Acanthopagrus australis 667 Girella tricuspidata 562 Mugil cephalus 520 Pomatomus saltator 211 Meuschenia freycineti 163 Meuschenia trachylepis 156 Monacanthus chinensis 152 Gerres subfasciatus 150 Merimbula Lake Girella tricuspidata 546 Meuschenia freycineti 106 Myxus elongatus 84 Achoerodus viridis 78 Gerres subfasciatus 76 Pseudocaranx dentex 69 Mugil cephalus 32 Monacanthus chinensis 24 176 catches of commercial species among the estuaries, with species such as Girella tricuspidata and Acanthopagrus australis consistently among the most abundant commercial species caught (Table 5.1). However, there were also some noticeable differences among estuaries. For example, low numbers of Girella tricuspidata were caught in Coila Lake, whereas the species was in high numbers in all other estuaries. The catch of Acanthopagrus australis was low in Burrill Lake and St Georges Basin (Table 5.1). Other species that contributed most to the abundances of these selected species were usuaHy from the Mugilidae family (mullet) and/or Monacanthidae family (leatherjacket). Pomatomus saltator was caught less consistently and in lower abundances (Table 5.1), probably a consequence of the methodology, which is biased against surface fishes (West 1993). The following sections deal with the recraitment processes of each of the major commercial species. Background information on each species is given in this section, combined with new data from this study examining the timing of recraitment of these species to ICOLLs in SE Austtalia. 5.3.2 Acanthopagrus australis (Gunther 1859) Previous studies Acanthopagrus australis is one of most important commercial and recreational fish species in the waters of coastal NSW. Acanthopagrus australis belongs to the Sparidae family and there are at least six other species of bream in Austtalia. Acanthopagrus australis inhabit estuarine 177 and coastal waters in Australia from Townsville in Queensland to the Gippsland Lakes in Victoria (Kuiter 1993). Many studies of Acanthopagrus australis recraitment have used gonosomatic indices to investigate peak spawning times. The most common suggestion is that there is a progressional peak in spawning with latitude, with spawning of Acanthopagrus australis during April/May in southem NSW to July/August in southem Queensland (SPCC 1981; Pollock 1982a). There are many different reports on the time of spawning, with variations in the peak spawning times along the coastline. In a study of the Clarence and Richmond Rivers in northem NSW, gonosomatic indices indicated that spawning of Acanthopagrus australis populations in these rivers occurred in winter, from May to September (West 1993). In Moreton Bay, peaks in the gonosomatic indices occurred in July and August (Pollock 1982b). Kesteven & Serventy (1941) reported peaks in the spawning of Acanthopagrus australis in April on the centtal coast of NSW, in May on the north coast of NSW and June in Queensland waters. For Botany Bay, Sydney it was found that spawning stared as early as Febraary and continued to June (SPCC 1981). Spawning Acanthopagrus australis are generally found in the coastal zones along open surf beaches and near the mouths of estaaries (Pollock 1982a; Pollock 1982b). It is generally thought that Acanthopagrus australis undertake pre-spawning migrations from estuaries to coastal waters, and travel northward along the NSW coast. The extent of these migrations has not been quantified but there is some evidence showing that bream move between estuaries and some individuals ttavel great distances along the coast (>500km) (West 1993). 178 The larvae and pre-settlement juveniles of Acanthopagrus australis have been reported to enter estuaries on the flood tide and to settle in the shallow water habitats, such as seagrass beds. It is thought they spend the first four months of thefr life in these areas before moving to deeper estuarine habitats. Postlarvae and juvenile Acanthopagrus australis (<40mm length) are most abundant in the estuary approximately two months after the peak spawning event (Munro 1949). 5.3.2.1 Discussion of Results In this study, juvenile Acanthopagrus australis were found in the shallow water seagrass habitat in all seven estuaries sampled. In the 946 samples, collected every three months between October 1997 to July 2000, a total of 2592 bream were caught and the fork length measured. Low abundances of Acanthopagrus australis were found in St Georges Basin, Burrill Lake and Merimbula Lake (Figure 5.2), and the highest catches were from Coila Lake, followed in decreasing order by Wallaga Lake, Lake Illawarra and Lake Conjola (Table 5.1). Patterns of Abundance in juvenile Acanthopagrus australis Abundances of Acanthopagrus australis were highly variable between locations within estuaries. Significant differences in mean abundances of Acanthopagrus australis between sampling event and location were found for six of the seven estuaries, the exception being Lake Conjola (Table 5.2). However, only a small proportion of the total variability was explained by the main effect of Location (Table 5.3), This indicates there was little consistency to the pattems of abundance of Acanthopagrus australis within these estuaries. In conttast, in Lake Conjola pattems in abundance of Acanthopagrus australis were consistent 179 2.0, Lake Illawarra St Georges Basin —•— entrance —•— central —A— upper 1.5- /I 1.0- 0.5- 1 A—A 0.0- i— •- m 'i"=• * --• 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Lake Conjola 2.0^ Burrill Lake 1.5- • 1.5- 1.0- 1.0- T A I 1 Si 0.5- 0.5- E 3 Z 0.0- IS H •—• —*-"H-^' 0.0- C a a—»--a- a-i-l-a a a a 1 S 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Coila Lake WaUaga Lake • 1.5- 1.0- \ 0.5- \ ^ \ . • * B 4 A ^ a • a - a -a -a' • 0.0- —I—I—I—I—I—1—I—I—I—I—I—I— a- a a 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Event Merimbula Lake 1.5- 1.0- 0.5- » 0.0- a'Aifiaa^ffi 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Event Figure 5.2: Mean numbers of juvenile Acanthopagrus australis captured at the entrance, central and upper locations of the seven estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled quarterly for two years. Data was log (x+1) transformed. Bars denote standard error. 180 Table 5.2: Analysis of Variance of the abundance of the five commercial fish species. Data has been log transformed. Mean square values are shown. Significance of the test is represented by *P<0.01; **P<0.00\. SPECIES Factor d.f Lake St Lake Burrill Coila Wallaga Merimbula Illawarra Georges Conjola Lake Lake Lake Lake Basin Acanthopagrus Location australis 2 1.8** 0.05 0.3 0.07** 0.16 0.03 0.06* SampUng Event 11 1.3** 0.13** 0.8** 0.10** 2.5** 1.2** 0.07** (SE) LxSE 22 0.3** 0.04** 0.2 0.08** 0.5** 0.4** 0.03* Girella tricuspidata L 2 1.5** 0.5* 1.7** 0.6** 0.03** 0.07 1.0** SE 11 1.0** 1.04** 0.9** 0.7** 0.08** 1.0** 0 9** LxSE 22 0.5** 0.4** 0.4** 0.2** 0.04** 0.3** 0.3 Meuschenia trachylepis L 2 Q 4*» J 4** J J** 0.09 na 0.9** na SE 11 0.5** 0.4** 0.7** 0.3** na 0.3** na LxSE 22 0.3** 0.2** 0.4** 0.1 na 0.2** na Monacanthus chinesis L 2 0.01 0.06 0.13** 0.03 na 1.0** 0.005 SE 11 0.003 0.09* 0.05* 0.03** na 0.3** 0.1** LxSE 22 0.005 0.08* 0.03 0.03** na 0.2** 0.004 Gerres subfasciatus L 2 3.5** na 0.5** 0.5** na 0.03 0.2* SE 11 0.3** na 0.5** 0.007 na 0.3** 0.2** LxSE 22 0.5** na 0.3** 0.01 na 0.09 0.2** 181 Table 5.3: Percentage variation in abundance of the five commercial fish species, explained by each term in the ANOVA model for each individual estuary. SPECIES Factor Lake St Lake Burrill Coila Wallaga Merimbula Illawarra Georges Conjola Lake Lake Lake Lake Basin Acanthopagrus Location australis 4.9 1.8 2.0 3.5 1.7 2.3 6.7 Sampling Event {SE) 29.8 34.5 18.5 21.8 37.2 19.5 22.3 LxSE 18.0 22.8 28.5 41.2 29.7 38.6 18.8 Girella tricuspidata L 9.0 3.1 11.5 6.1 2.8 0.5 9.6 SE 33.6 37.0 33.8 36.2 40.0 40.5 30.3 LxSE 29.3 28.0 26.1 19.5 36.9 24.0 18.3 Meuschenia trachylepis L 5.1 14.0 11.4 1.5 na 14.1 na SE 32.6 18.5 35.6 24.5 na 22.1 na LxSE 38.3 26.0 42.1 20.1 na 30.2 na Monocanthus chinesis L 3.3 1.8 7.7 8.0 na 15.8 0.7 SE 6.2 15.2 17.3 36.3 na 26.4 38.3 LxSE 19.2 29.0 20.1 59.3 na 38.3 3.8 Gerres subfasciatus L 23.4 na 6.5 9.2 na 0.5 5.5 SE 12.2 na 36.1 7.6 na 27.1 17.0 LxSE 33.5 na 37.6 22.0 na 17.0 37.2 among sites between sampling events. Persistent differences between sampling events were detected by a large proportion of the total variation by the sampling event factor in the ANOVA (Table 5.3). This was particularly evident for Lake Illawarra, St Georges Basin, CoHa Lake and Merimbula Lake, where between 22 and 37% of the variation in abundance of Acanthopagrus australis could be attributed to the main effect of Sampling Event (Table 5.3). While there were few consistencies in peaks in the population of juvenile Acanthopagrus australis between estuaries, some pattems were observed. A substantial increase in the 182 number of small Acanthopagrus australis individuals occurred in October 1998 for all estuaries (Figure 5.2). A peak in abundance also occurred in the same period the following year, but was only evident in Lake Hlawarra, Coila Lake and Wallaga Lake. A peak in recmitment also occurred in July 2000 for Lake Illawarra, St Georges Basin, Lake Conjola and Burrill Lake. Notably this did not extend to the lakes further south, where no individuals of Acanthopagrus australis were caught in any of the locations within Coila Lake, Wallaga Lake and Merimbula Lake (Figure 5.2). For Coila Lake this could be explained by an enttance closure, but the other lakes were open to the ocean at this time. Length frequency of Acanthopagrus australis Miskiewicz (1987) has reported that Acanthopagrus australis were caught as plankton along the NSW coastline at a size of 10-30mm. In the present study postlarvae and young juveniles less than 40mm in fork length were taken from seagrass beds in all lakes, including individuals as small as 10mm. The majority of individuals were caught in the size range of 10-30mm. In the following sections, detailed analysis of length-frequency information and timing of recmitment events has been carried out for catches from Lake Illawarra, Lake Conjola, Coila Lake and Wallaga Lake, where the greatest numbers of Acanthopagrus australis were caught. In Lake Illawarra, very few Acanthopagrus australis were caught during the first year (Sampling Events 1, 2, 3 and 4) (Figure 5.3), and the main peak in abundance occurred in October 1998 with the majority of individuals 10-40mm (Figure 5.3A). These were found at all locations, with the largest concentration found at the upper location (Figure 5.3B). Higher 183 numbers of Acanthopagrus australis of the size 10 to 120mm were then caught during the next three sampling events. At the next sampling event (Febmary 1999) larger size classes were caught (10-70mm FL), exclusively at the centtal and upper locations (Figure 5.3B). The next major peak in abundance occurred in July 2000, with fish in the size range of 10-20mm (Figure 5.3A), caught at all locations. The high recmitment that was evident in October 1998 was not repeated the following year, with only a weak peak in abundance in October 1999 (Figure 5.3A). Three main peaks in abundance of postlarval and juvenile Acanthopagrus australis were observed in Lake Conjola, namely in; October 1997, October 1998 and July 2000, with only a small number of recmits caught in July and October 1999 (Figure 5.4A). However, the recmitment event of October 1998 was by far the strongest with approximately six times the number of Acanthopagrus australis caught that in either the previous or preceding year (Figure 5.4A). Most individuals were 10 to 30mm in length (Figure 5.4A). There was little consistency between recmitment locations for Acanthopagrus australis in Lake Conjola. Small individuals concentrated at the enttance in October 1997, at the central location in October 1998, and at the upper location in July 2000 (Figure 5.4B). 184 (A) (B) Octol)erI997 I I—I—I—I—:—I—1—I—I—I—I—I—I—I 10 20 30 « 50 60 70 80 90 100 110 120 130 1* 150 October IMS Fel)nBO'1998 fkdrance -1—r—I—I—I—I—I—I—I—I—I—I—I—I— 10 20 30 40 60 60 70 80 90 100 110 120 130 140 0-1—^—I—1—I—I—I—I—" —^^^^^r I—I—1—1—r 5IJ 0 10 20 X « 50 60 70 80 90 100 110 120 130 140 150 AfAWS Central -1—I—r 1—I—I—I—i—I—I—I—I—I—I 1 10 20 30 40 50 70 90 100 110 130 130 140 19 00< eo a) 1QQ 0 10 20 X « 50 60 TO 80 90 lOO 110 120 130 140 160 July 1998 Upper 60- 1 1 "1- "1 • I" 1 1 1 1 1 1 1 1 1—I—I—I—I—r—I—I—I—I 3 10 20 30 40 60 60 70 r 90 100 110 120 1X 140 IS 0 10 20 X 40 50 60 70 80 90 100 110 120 130 1« 150 60 Fni FebnBryl999 Entrance t I—I—I—I—!—I—I—I—r- m. • Central 25- ) 10 20X40506070809rh 0 100 110 120 IX 1« IX 50. Upper r1 1l 1 1 fh1 1 1 1 1 J 10 2030405060706090 100 110 120 IX 140 IX Fork length (im^ Jidy20Q0 EbliBnce I—I—I-~i—1—1—I—I—I—I—I—I—I—I—I 51)5 10 20 X 40 50 X 70 80 9D IX 110 120 IX 140 IX Catrd 1—I—I—I—I—I—I—I—I—I—1—I—I SQ 0 10 20 X 40 X ffi 70 X X IX 110 120 IX 140 IX Uppff 1^—I—I—I—1—I—i—I—I—i—I—i—1—I 0 10 X X 40 X X 70 X X iro 110 120 1X 140 IX Fakiaiatti(imt Fork lenglh (mrr) Figure 5.3: (A) Size composition of Acanthopagrus australis caught in Lake Illawarra over the three-year sampling period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Lake Illawarra have been shown. 185 (A) (B) 50 October 1997 25- October 1997 Qiraace I . . . T 1 1 1 1 1 1 1 1 1 1 50 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Fd>niaiyl998 oH—^—I—I—I—I—I—I—I—I—I—I—1—I 25- _ i0 1k0 a X 40 X ffl 70 m so IX 110 120 IX 140 IX Gmtral 0 —I 1 1 1 ! 1 r- —1 1 1 1 1 1 1 10 20 30 40 50 60 70 90 100 110 120 130 140 150 J 25- 50-y E April 1998 3 Z —1—I—I—I—I—I—I—i—I 0 10 a X 40 70 ffl X 1X 110 IX IX 140 13 (— r —T— 1 —I— —T——I — —1—1—1—r—1—1 •0- ) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 July 1998 s- I—I—I—r~i—!—I—I—I—I—t—I—[—I—I 0 10 a X 40 X ffl 70 X X IX 110 ia IX 140 IX 1 r 1 1 J 1 i r 1 1 I 1 1 Farklenc^(iTiTt 50 ) 10 20 30 40 60 70 80 90 100 110 120 130 140 150 October 1998 October 1998 f^itrance 10 20 30 40 50 60 70 100 110 120 130 140 150 Februaiyl999 I I I—I—I—I—I—I—I—I—I—I—I—1—I 0 10 X X 40 X X 70 X so IX 110 IX IX 140 IX —I 1 I I I I I I I 1 1 1 1 1 1 Central 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 April 1999 1—I—I—I—I—I—I—I—I—1—I—I A5 10 a X 40 X X 70 X X IX 110 1X IX 140 IX -1—I—I—nn—I—r^—i—i—i—i—i—i—i 10 20 30 40 so 60 70 80 90 100 110 120 130 140 160 Dipper July 1999 T 1 1 1 1 1 1 I I 1 1 1 p 1 1 1 1 1 1 1 1 1 X iro 110 ia IX 140 ix 10 20 30 40 60 60 70 80 90 100 110 120 130 140 150 Rjk length (mr) October 1999 Jiiy2000 Entrance .) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 160 February 2000 1~ 1—I—I—I—I—I—I—I—I—I—I—I—i—I 10 a X 40 X X 70 X X IX 110 la IX 140 ix 1 1 1 1 1 1 1 1 1 1 1 1 1 1 50 80 0 10 20 30 40 60 70 90 100 110 120 130 140 150 Cenlial April 2000 3 z —I 1 1^ 1 1 1 1 1 0- 10 a X 40 X w 70 ffl X im 110 ia IX 140 ix 10 20 30 40 50 70 80 90 100 110 120 130 140 150 July 2000 ihM- 25- -1 1 1 1 1 1 1 1 1 1 1 1 0- L 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 ) 10 20 X 40 » 60 70 80 90 IX 110 120 IX 140 IX Fork length (mm) FarklenE^(nTr| Figure 5.4: (A) Size composition of Acanthopagrus australis caught in Lake Conjola over the three-year sampling period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Conjola have been shown. 186 Thus, for Lake Illawarra and Lake Conjola a general recruitment period for Acanthopagrus australis occurred during the spring/summer period from September/October to Febmary. The recruitment event that was evident in July 2000 for 4 of the 7 estuaries (Lake Illawarra, St Georges Basin, Burrill Lake and Lake Conjola) indicates that recmitment can be quite protracted. A similar situation was found in Botany Bay, Sydney, where individuals less than 20mm were caught, from April to August (SPCC 1981). The recmitment of Acanthopagrus australis into Coila Lake was largely governed by the timing of the mechanical opening of the entrance during the three-year period. Individuals of Acanthopagrus australis were caught on only foiu* of the sampling occasions (Figure 5.5). The major recraitment event that occurred across all estuaries (during October 1998) was also evident in Coila Lake. Large numbers of postlarval Acanthopagrus australis in the size range of 10 to 20mm were caught during this period (Figure 5.5). On the next sampling occasion in Febmary 1999, Acanthopagrus australis in the size range 80 to 120 mm were caught, suggesting either a very fast growth rate or a different cohort of fish (Figure 5.5). There was a large peak in abundance during April 1999 with individuals less than 30mm. Poor recmitment occurred in October 1999 with juveniles between 30 to 70mm caught (Figure 5.5). Acanthopagrus australis were caught on all sampling occasions in Wallaga Lake between October 1997 and October 1999, with no individuals caught in the period from Febmary to July 2000. There were major peaks in abundance in July 1998, October 1998 and April 1999, with smaller recmitment events during July-October 1999 (Figure 5.6A). Like Lake Conjola, the catch of Acanthopagrus australis in Wallaga Lake in October 1998 was by far the highest, with numbers being 1.5 times higher in this period. The majority of the Acanthopagrus 187 australis catch during these peak abundance events were postlarval fish, less than 30mm in length. Similar to the other lakes, juvenile Acanthopagrus australis between the size of 40 to 90mm were caught during Febmary 1999. In Wallaga Lake, new recmits were found in similar numbers at the entrance, central and upper locations during April 1998 (Figure 5.6B). The inconsistent pattem of distribution of postlarvae Acanthopagrus australis that was noted in the other estuaries was also found in Wallaga Lake. During the peak recmitment event of October 1998 the majority of the catch i0-20mm in length was found at the upper lake location. Conversely, in the next recmitment event (April 1999) individuals 10-3 0mm in length caught at the entrance site (Figure 5.6B). Ckloberl996 0- "I I I I 1 I I I 1 I I I 0 10 aD M 40 SD eo 70 80 90 100 110 120 130 140 150 BaruaayUW B 100- 3 z -\—I—I—I—I—I—r T 1 1 0 10 20 M 40 aO eo 7D 80 go 100 110 120 130 140 150 an-I Apill999 100- -l—I—I—I—l~~l—I—I—I—I 0 10 20 30 40 50 60 70 80 90 100 110 120 IX 140 ISO TSXtr October 1999 100- T 1 1 I I I I 1 1 1 1 1 1 1 1 0 10 20 » 40 a) eo 7D 80 90 100 110 120 130 140 ISO Foricleri^th (iTTT^ Figure 5.5: The number of Acanthopagrus australis at each 10mm length interval at the peak recruitment times for Coila Lake 188 (A) (B) ICD. October 1997 SO- Ji4yl998 EKrance -I—t—r T—r ~ I I I I I I ,0 ioao»40BDeDioaD 90 10D 110 12D 130 140 190 Htetayl998 n—r- . 0 10 20 30 « 50 -r~i—I—I—I—I—I—I—I—I—I—I—I—I—I April 1998 •!—I—I—I—I—I—I—I—I—I—I—I 10 20 30 40 50 60 7D 60 90 IX 110 120 130 140 150 0- Vppa 1 1 1 1 1 1 1 1 1 1 T 1 1 1 10 20 40 60 60 70 83 SO 100 110 120 130 140 19D 1CD- Myim BO- 11 —I—I—I—I—I—I—I—I—I—I L0 10 20i X « 50 60 70 60 90 100 110 120 1» 140 ISO 1 Rifkien^(nni) 1 1 1 1 1 1 1 1 1 1 1 ) 10 i20 L» 40 60 80 70 80 so 100 110 120 130 140 190 0[tab»-1998 October 1998 Entrance -1 1 1 1— -1—I—I—I—I—1—I—I L10 LX X 40 X X 70 X X IX 110 120 IX 140 IX Fei>nia>yl999 JQ X- E Central -1—I—I—I—I—r~i~~^—I—I—1—I—I—I S so- 10 20 X 40 X X 70 X X iro 110 120 130 140 IX April 1999 »H—I—P—1—1—r- 0 10 20 30 40 so Upper -1 1—I—I 1—I 1—I—I—i— lU10 X X 40 X X 70 X X IX 110 120 IX MO IX Jiiyl999 —I—I—I—I—I—I—1—I—I—I ±0 10 2) X 40 so X 70 80 90 IX 110 IX IX 140 1S0 Ftrkien^trnn) 1—1 1 1 1—I—I—I—I 1 1—I 10 X X 40 X X 70 X X IX 110 IX 1X 140 IX October 1999 April 1999 -|—I—I—I—I—r 3 10 X X 40 X X 70 X X 1» 110 IX IX 140 IX IX. I I I II l~ I I I I I I Fetiiaiy2000 , L0 10 Lffl X 4 0 X ro 70 X X IX 110 IX IX 140 IX X- Central 1 —r "I— -r 1 1 1 1 1 1 1 1 1 ,^ J 10 -| X -| X X IX 110 IX IX 140 IX I.. X X 40 X 70 1 1 1 —,—J— —I— - T—r- I April 2000 10 20 X 40 50 ro 70 X X IX 110 IX IX 140 IX 1X. Upper -1 1—I—I 1 1—I 1—I 1—I 1—I—I—I »- 10 X X 4a X X 70 X X IX 110 IX IX MO IX 1 1 1 1 1 1 1 1 1 July200O 10 X X 40 ro 70 X X IX 110 IX IX 140 150 X- Fo(1< len^h (nvn) 0 -I—I—I—I—I—I—1—I—i—I—r—I—I—I—I 10 X X 40 X X 70 X X IX 110 IX IX MO IX FQri Figure 5.6: (A) Size composition of Acanthopagrus australis caught in Wallaga Lake over the three-year sampling period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Wallaga Lake have been shown. 189 While, the timing of recmitment of Acanthopagrus australis in Wallaga Lake was similar to the other estuaries (i.e., spring/summer period), the recmitment of this was also quite prominent in the period April to October, indicating slight latitudinal differences in the timing of peak recmitment events along this section of coast. 5.3.3 Girella tricuspidata (Quoy and Gaimard 1824) Previous studies Girella tricuspidata belongs to the Girellidae family, and is found in nearshore coastal waters and estuaries, from Hervey Bay in Queensland to Kangaroo Island in South Australia, as well as waters of Tasmania and parts of New Zealand (Kuiter 1993). Girella tricuspidata are believed to be only moderately fished, but this finding is based on poor data and a preliminary assessment (NSW Fisheries 2002). Tagging studies in NSW have shown that Girella tricuspidata can travel between estuaries, both in a north and south direction along the coast (Thomson 1959; West 1993; Gray & Miskiewicz 2000). This indicates that probably only one genetic stock exists along the eastem Australian coast. Reproductive studies on Girella tricuspidata are limited, but mature fish undertake pre- spawning runs from rivers and estuaries to the ocean. It is generally assumed that Girella tricuspidata spawn in the coastal zone along surf beaches and near the mouth of estuaries. There appears to be a latitudinal gradient in the timing of spawning, from July to September in southem Queensland and northem NSW, August to December in central NSW, and October to March in central Victoria (Kailola et al 1993; West 1993). The larvae of Girella tricuspidata settle in shallow seagrass beds for the first few months before moving to mangrove creeks and 190 rock walls. In central NSW Girella tricuspidata larvae have been caught between September and January (Miskiewicz 1987), and in Botany Bay (Sydney) postlarval Girella tricuspidata were foimd between October to December (SPCC 1981). 5.3.3.1 Discussion of Results Patterns of Abundance in juvenile Girella tricuspidata Girella tricuspidata were found in all estuaries, with a total of 3369 individuals caught over the three-year period. The highest abundances were found in St Georges Basin, followed by Lake Illawarra, Wallaga Lake and Merimbula Lake (Figure 5.7). Low numbers of Girella tricuspidata was caught in Coila Lake (Table 5.1). With the exception of Merimbula Lake, the mean abundances of Girella tricuspidata fluctuated significantly among localities and between sampling times, displayed no consistent inter-estuary pattem (Table 5.2). Inconsistent differences in the abundances of Girella tricuspidata among sampling events accounted for the largest amount of variation in the ANOVA model, while the effect of location within an estuary was weak (between 0.5 to 11.5%) (Table 5.3). Length Frequency of Girella tricuspidata The timing of recmitment of Girella tricuspidata along the south-eastem coast of NSW appears to occur fi-om October to Febmary, but the strength and timing changed slightly on a latitudinal scale. Detailed recmitment information will focus on Lake Illawarra, St Georges Basin, Wallaga Lake and Merimbula Lake. 191 Lake Illawarra St Georges Basin —•— entrance • central *• upper 4 lit - ^ I 1 1 1 1 1 1 1 1 1 1——r 1— 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2t00 4/00 7/00 10/97 ZraS 4/98 7/98 10/98 2/99 4/99 7/99 10«9 2A)0 4/OQ 7/00 Lake Conjola Burrill Lake • ^ E A a a 1 A 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Coila Lake Wallaga Ldce 2.0- 2.0- 1.S- 1.5- i • • 1.0- 1.0- • * • • • 0.5- 0.5- • \ • 1 A t A 0.0- a a a «- 0.0- « • —a a —1 1 1 1 1 1 r 1— • 1 I 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2A)0 4/DO 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 SampHng Event Merimbula Lake 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2A)0 4/00 7/00 Sampling Event Figure 5.7: Mean number of juvenile Girella tricuspidata captured at the entrance, central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake, which was sampled quarterly for two years. Data was log (x+1) transformed. Bars denote standard error. 192 The main period of recmitment of Girella tricuspidata for Lake Illawarra occurred during October in the first and second year and in April and July in the third year. Postlarval Girella tricuspidata were found during most sampling events within Lake Illawarra (Figure 5.8A), however there were notable peaks in recmitment during October 1997 and 1998 (Figure 5.8A). Smaller numbers of newly-settled larvae were caught during the months of Febmary, but these were mamly larger juveniles of 40-80mm fork length. During the third year postlarval Girella tricuspidata were also caught during October and Febmary, but the most notable recmitment was during July 1999 and April 2000 (Figure 5.8A). Distribution of newly-settled larvae between the entrance, central and upper locations within Lake Illawarra also varied over time (Figure 5.8B). During October 1997, Girella tricuspidata 10-30mm in fork length were only caught at the entrance location, while the following year during October 1998 individuals less than 40mm were caught at all locations with the highest number caught at the central location. The situation changed again during April 2000 when the majority of Girella tricuspidata were found at the entrance (Figure 5.8B). In St Georges Basin new recmits less than 40mm fork length were evident during the period October to Febmary during the first two years of sampling, and this appeared to be the main recmitment time. During the last year, from October 1999 to Febmary 2000, very few postlarval Girella tricuspidata were caught, with reasonable catches only during the Febmary sampling event (Figure 5.9A). The major peak in recmitment of Girella tricuspidata occurred during October 1998, where there was a five-fold increase in the abimdance of Girella tricuspidata compared to other periods. The pattem of distribution of newly settled larvae within St Georges Basin differed between locations and sampling time (Figure 5.9Bb). For example, during Febmary 1998 and 1999, new recmits of a size 10-40mm were caught at the 193 (B) October 1997 i OclobH-1997 I I I I I I I I I I I I ggO 10 20 30 40 50 60 70 80 90 100 110 120 1X 140 150 -1—I—I—I—I—i—I—I—1—I—I—I February 1998 50 \k0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Cmtral —1—I—I—r~T—I—I—I—I—1—I—I 20 30 40 so 60 70 80 90 100 110 120 130 140 150 AprQ199S -1—I—I—I—I—I—1—I—I—I—I—I—I—I—I 25 50 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Upper —I 1 1 ^ 1 1 1 1 1 1 1 40 50 60 70 80 90 100 110 120 130 140 150 Jiilyl998 "H—I—I—I—I—I—I I I—I—I—I—I—I—I—I 0 10 20 30 40 50 80 TO 83 90 100 110 133 1» 140 ISO Folk lenglti(nii| -1 1 1 1 1 1 1 1 1 1~~1 1 l~~l 1 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 October 1998. ~ I 1 I L 1 1 I 1 i I 20 30 40 50 60 70 80 90 100 110 120 130 140 150 February 1999 1—I—r—T—I—I—I—I—I—I—I—I ,(jlJ> 10 20 M 40 50 eo 70 80 so 100 110 120 130 140 150 -I 1 1 ( 1 1 1 Central 20 30 40 50 60 70 80 90 100 110 120 IX 140 150 April 1998 —I—1—I—I—I—1—I—I—I 1—I ^ffjOa 10 20 30 40 5 0 60 70 80 so 100 110 120 130 140 150 —I 1 1 1 1 1 1 1 1 1 1 1 Upper 10 40 50 60 70 80 90 100 110 120 130 140 150 July 1999 I—I I I—I—I—I—I—I—I—I—I—I—I—I 0 10 20 X 40 50 60 70 80 so 10O 110 120 130 140 150 T 1 1 1 r I P—I—1 1 1 1 ; Forit length (im^ 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 October 1999 A|]rjl2000 I I 1 1 1— —I 1 1 1 1 1 EninaKe 20 30 40 50 60 70 80 100 110 120 130 140 150 February 2000 1—I—^—I—t—t—[ 1—1 1 "~1 1 1 1 1 1 1 1 1 1 1 1 f 6g0,L 0 10 2L3 X 40 50 60 70 80 90 1X 110 120 130 140 150 40 60 60 70 80 90 100 110 120 130 140 150 Central April 2000 I I I 1 1 1 1 1 1 1 1 -1—I—I—r 20 30 40 SO 60 70 80 90 100 110 120 130 140 150 g, 0 10 X X 40 X 60 70 X X 1X 110 120 1X 140 IX July 2000 l*per —I—r~~i—I—1—I—I—I—I—I—I—I oH—I—I—I—t—I—I—I—r-T—I—I—I—I—I—I 0 10 40 50 60 70 80 90 100 110 120 130 140 150 0 10 X X 40 X X 70 X X IX 110 133 IX 140 IX R>rk length (mm) FQriclenglh(iiii| Figure 5.8: (A) Size composition of Girella tricuspidata caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recmitment events distribution of individuals among locations within Lake Illawarra have been shown. 194 (B) 50 (A) October 1997 26- FEbiuylWS 0 "1 I 1 l~~l 1 1 1 1 1 1 75 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 50- ^m FebrDaiyl998 n—I—I—I—I—I—I—i—I—I—I—I 25 SOJ) 10 20M4O50607D8O 90 100 110 120130 140150 0 —1 1 1 1 1 1 1 Central 50 0 10 20 30 40 50 60 70 90 100 110 120 130 140 150 I 25 April 1998 26' l-T 1—I 1 1 1 1 1 1 1 50i) 10 2030405060708090 IM 110 120 130 140 150 -r I I I I I Upper 55 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 July 1998 25H ^—I—I—I—I—I—I—I—I 1—I 0 10 20 X 40 50 W 70 80 90 100 110120130 140 160 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Forl(len0i(imt 200-1 ISO October 1998 100 50 0 60 J.0V 10 20 l30 4 0 50 60 70 80 90 100 110 120 130 140 150 February 1999 -1—I—I—I—I—I—I—I—I—I—I—I—I—I I 25. joo-P 10 20 30 40 60 60 70 80 X 100 110 120 130 140 160 Oailral 0 T—r~~i—I—I—I—I—1—I—I—I—I 100- ^H 50-0¥ 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 April 1999 25 0-1—^W- 200-9 10 20 30 40 50 60 70 80 90 100 110 120 IX 140 160 -1—I—n'n—r -r —1 1 1 1 1 1 1 \ Uppa- soil 10 20 30 40 50 60 70 90 100 110 120 130 140 150 10O July 1999 25- I PH 0 10 20 30 40 50 60 70 80 90 100110 120 130 140150 I ' I—r"~i—I—I—I—1—I—I—I—I—I—I—I 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Faiklenglh(inT4 50 October 1999 25- 60-1 Fd]niaiyl999 0 I I 1 1 1— —1 1 1 1 1 1 1 1 1 25- 50^1 10 20 30 40 50 70 80 90 100 110 120 130 140 150 February 2000 ^—I—I—I—I—I—1—I—I—1—I—I—I 60.(l 10 2030406060708090 100 1101201X140150 0 T I I I I r I I I I I Central 50-? 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 April 2000 25- 1 f~~l 1 1 1 1 1 1 1 1 1 0 —^ 1 1 1 1 1 1 1 r 1 r 1 Sofi 10 20 X 40 60 60 70 W M IX 110 IX IX 140 IX 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Upper 50-' July 2000 25- 25- 0 ^ 1 1 1 1 1 1 1 1 \ 1 1 1 0 —1 ^^ 1 1 1 1 1 1 1 1 1 1 0 10 X X 40 60 X 70 X » IX 110 IX IX 140 IX 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 Fork length (imf Fork length (mm) Figure 5.9: (A) Size composition of Girella tricuspidata caught in St Georges Basin over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within St Georges Basin have been shown. 195 entrance, central and upper locations, while during the major recmitment event of October 1998, the majority of individuals 10-30mm in length were captured at the central location (Figure 5.9B). The main recmitment period for Girella tricuspidata in Wallaga Lake occurred during October to April. Again, October 1998 was a particularly strong recmitment time (Figure 5.10A). During the third year, recmitment was weaker than for the previous two years, with individuals less than 40mm only caught during October 1999. Newly-settled larvae were caught at the entrance, central and upper locations within Wallaga Lake but the number of individuals at each location changed with time (Figure 5.10B). For example, the highest abundance of individuals less than 30mm were caught at the entrance in April 1998, but during October 1998 the highest number of postlarval Girella tricuspidata were caught at the upper location (Figure 5.1 OB). The timing of recmitment of Girella tricuspidata in Merimbula Lake was slightly different to the other lakes, with the peak recmitment evident during the month of Febmary. Unlike the other lakes very few individuals were caught during either October or April (Figure 5.11 A). The majority of Girella tricuspidata less than 40mm were caught at the entrance location of this lake (Figure 5.1 IB). 196 (A) (B) Ortnba-1997 AprflUW T—I—I—r~-\—I—1—I—I—I 0 10 X X 40 X X 70 X M IX 110 ia IX 140 IX X February 1998 25- n—[—1—I—I—I—I—I—I—I 50J) 10 X X 40 X X 70 X X IX 110 1X 1X 140 1X -| 1 1 i 1 1 1 1 Coitral 40 X X 70 X X 1X 110 IX IX 140 1X 125^ E April 1998 ^—I—I—I—I—I—I—I—I—I 50 0 10 X X 40 X X 70 X X 1X 110 IX 1X 140 1X Upper T 1 1 1 1 1 1 1 1 0 10 a X 40 X X 70 » X IX 110 IX IX 140 IX 25- July 1998 0 10 X X 40 X ffi 70 X X IX 110 IX 130 140 1X Forte length (nnif I I I—I—I I I—I—I—I—I—I—I—I—I 0 10 20 X 40 X X 70 X X 1X 110 ia IX 140 IM IX Octoba-1996 October 1998 IX- X- -|~n 1 1 1 1 1 1 1 1 1 0 10 a X 40 X X 70 X X IX 110 ia IX 140 IX S0•^u . 50JjIl 10 LX X 40 X ffl 70 X X IX 110 IX 1X 140 1X February 1999 & Ontral .a 25 E -t~~l 1 1 T 1 1 1 1 i 0 10 a X 40 X X 70 X X IX 110 ia ix 140 ix ^—I—I—r^—I—I—I—I—I—I—I—t- ,Ooil 10 X X 40 X X 70 X X 1X 110 IX IX 140 IS April 1999 \ X- 75 Vppar X 25- -1 1 1 l~~l 1 1 1 1 1 1 25 40 X X 70 X X IX 110 ia IX 140 IX 0' 1—I—I—I—I—I—I—I—I—I—I—1 July 1999 i0 1k0 X X 40 X X 70 X X IX 110 IX IX 140 IX 25- Rxklen0h(niTi| 0 T^ 1~~1 1 1 1 1 1 1 1 0 10 a X 40 X X 70 X X IX 110 ia IX 140 IX FebnBiyl999 Octoberl999 25- ^ 10 X X 40 X X 70 X X 1X 110 1X 1X 140 IX 0- ^—^—I—I—I—I—I—I—I Central ggO 10 a X 40 X X 70 X X IM 110 ia 1X 140 1X Febniaiy2000 25- ^n—I—I—1—1—I—I—I—I—I—\—I—I—I 50i) 10 X X 40 X X 70 X M IX 110 IX IX 140 1X -| 1 r T 1 1 1 1 1 1 1 UHxr 0 10 a X 40 X X 70 X X IX 110 ia IX 140 IX April 2000 I I I I I I 1 1 1 1 1 1 1 1 1 0 10 X X 40 X X 70 X X IX 110 1X 1X 140 1X Folic length (nnt 1 —I— —I— 1 —I— —f -Tf——t — 1 —1—1 —r 1—1 1 3 10 X 40 X X 70 X X . a IM 110 ia IX 140 IX July 2000 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ) 10 a X 40 X X 70 X X IM 110 ia IX 140 IX Fork length (mr^ Figure 5.10: (A) Size composition of Girella tricuspidata caught in Wallaga Lake over the three-year period, separated into the twelve samphng events. (B) For peak recruitment events distribution of individuals among locations within Wallaga Lake have been shown. 197 (A) (B) 50- OUterWi Febnaiyl999 EOnax ll T—r- "I~~1 1 1 1 \ 1 1 1 1 1 60 60 70 a) 90 100 110 120 133 140 150 -I—I—r n—I—I Rbn«yl999 10 a X 40 X ffl 70 X X ix 110 ia IX 140 IX GeOrd ,0 10 20 33 40 E 25- T"~l I I I I I I I I I B 5QO 10 20 30 40 50 eo 70 eo go loo no 120 i30 i40 150 1—1—I—I—I—I—;—I—1—!—I—I /^nll999 10 a X 40 X ffl 70 x X IX 110 ia IX 140 ix 25- x-P '-I ^^^^- liper 1—r T 1 1 1 1 1 1 1 1 50 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 JUyl999 1—I—^—r-1—I—I—I—I—I—I—1—I—I 5 25 0 10 a X 40 X ffl 70 X X IX110 ia IX 140 IX E T—I—1—r- -| (~~l 1 1 1 1 1 1 1 1 0 10 20 30 40 50 60 70 80 90 100 110 123 130 140 150 Ouotaa-isgg 75n FEJbruaiy 21X10 X- ^_ EUrame I I I—I—I—I—I—1—I—I—I 1 25- 50 eo 70 80 90 100 110 120 130 140 150 L Fdnaiy2ixn 75- ) 110 a X 40 X ffl 70 X X IX 110 ia IX 140 IX Catia T 1 1 1 1 1 1 1 1 1 1 8 50n0 10 20 X 40 50 eo 70 80 90 100 110 120 130 140 150 Numbe r A|nl2000 K 25. o 1 10 a X 40 ffl ffl 70 X X IX 110 ia IX 140 IX S I X- liper 3 10 2D 30 40 50 eo 70 80 90 100 110 120 130 140 150 50- 25- July 2000 25- ~1 1 1 I 1 1 1 1 1 1 1 1 1 1 3 10 a X 40 X ffl 70 X X IX 110 ia ix 140 IX Fcriclen^(nn) II 1 1 1 1 1 3 10 20 30 40 50 eo 70 80 90 100 110 120 130 140 150 Forklan0i(iTiTt Figure 5.11: (A) Size composition of Girella tricuspidata caught in Merimbula Lake over the two-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Merimbula Lake have been shown. 198 5.3.4 Meuschenia trachylepis (Gunther 1870) Previous studies Meuschenia trachylepis belongs to the Monacanthidae family of which is represented by 27 genera and almost 60 species in Australia (Kuiter 1993). Meuschenia trachylepis is an oceanic species but is dependent on the estuarine habitat as juveniles. The adults are believed to spawn in inshore habitats close to the entrance of estuaries (SPCC 1981). Biological and fishery-related information for Meuschenia trachylepis is extremely limited as it is for most leatherjacket species. For example, it is not presently possible to determine conmiercial fishery catch rates on individual leatherjacket species (NSW Fisheries 2002). For the Estuarine General Fishery in NSW, leatherjacket species are combined into a non-descript "leatherjacket (all)" category, which appears to be generally composed of yellow-finned leatherjacket, variable leatherjacket and fan-bellied leatherjacket. This is a critical point especially given that catch rates in the estuary general fishery have declined from 40 tonnes in the 1980s to approximately 15 tonnes in the late 1990s (NSW Fisheries 2002). The leatherjacket fishery has previously been severely fished and now, while considered a by product species is regarded as fully to overfished (NSW Fisheries 2002). Stock assessments of leatherj ackets are very poor based on little data and almost no life history information. Little is known about the time of spawning and recruitment of Meuschenia trachylepis along the NSW coast. The main recruitment period of Meuschenia trachylepis in Botany Bay (Sydney) was found to occur from October to December, with peaks mainly in December (SPCC 1981; McNeill et al 1992a). Similarly, recmitment of Meuschenia trachylepis to 199 Zostera beds within Lake Macquarie occurred mostly during October to November, and were concentrated in a zone near the entrance (Hannan & Williams 1998). 5.3.4.1 Discussion of Results Over the three-year sampling period a total of 1142 Meuschenia trachylepis individuals were caught in the seven estuaries. The highest catches of Meuschenia trachylepis were made in St Georges Basin, followed by Lake Illawarra and Lake Conjola. Only one individual was caught in Coila Lake and nine in Merimbula Lake (see species table, Chapter 3). Due to these low catches, these latter two lakes will be excluded from further analysis. Patterns of Abundance of Meuschenia trachylepis There were significant differences in the abundances of Meuschenia trachylepis, both spatially and temporally for Lake Illawarra, St Georges Basin, Lake Conjola and Wallaga Lake (Table 5.2, Figure 5.12), and the interaction ofthese factors explained the largest amount of variance in the ANOVA model (Table 5.3). The interaction of time and location was not significant within Burrill Lake, but there were consistent differences in the abundance of Meuschenia trachylepis throughout time (Table 5.2). 200 Lake Illawarra 2.0 ^ St Georg es Basin —•— entrance —•— central ^*- upper 1.5- 1.5- 1 • 1.0- 1.0- \^ i • • • * * 0.5- i 0.5- \ t /*> 0.0- •- '^m—tf I A * « • ft H 0.0- • — 1 —1— 1 1 1 1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 2.0-, Lake Conjola Burrill Lake 1.5- ' t ;- 1.0- 8" O.S- A 0.0- -m- k 1 1 1 1 —1 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Coila Lake Wallaga Lake • A * * ^ \ A ' ' - m « 1 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2^)0 4/00 7/00 Sampling Event Merimbula Lake —I 1 1 1 1 1 1 1 1 1 1 1— 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Event Figure 5.12: Mean numbers of juvenile Meuschenia tracttylepis captured at the entrance, central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled quarterly for two years. Data was log (x+1) transformed. Bars denote standard error. 201 Length Frequency of Meuschenia trachylepis The recruitment period of Meuschenia trachylepis appears to occur during October, and probably extends to December. A range of length sizes of Meuschenia trachylepis was caught by the sampling method. For example, within Lake Illawarra large juveniles 40-110mm in length were caught during October 1997 and February 1999 (Figure 5.13A). Abundance of new recruits (<40mm) was considerably higher during October 1998, compared to 1997 and 1999 (Figure 5.13A). The majority of these new recruits were caught at the central location (Figure 5.13B). No individuals at all were caught in the period October 1999 to July 2000 in Lake Illawarra. While the highest number of Meuschenia trachylepis were caught in St Georges Basin, the majority of the catch were large juveniles, greater than 70mm in size. These large juveniles and other sub-adults were caught on all sampling events (Figure 5.14A). There was only one major recruitment event of Meuschenia trachylepis that was detected by this study and it occurred during October 1997, when large numbers of individuals 10-20mm in size were caught (Figure 5.14A). The majority of the catch was from the entrance location, with lower numbers found at the central location (Figure 5.14B). During October 1998, new recmits were caught again, but considerably less than the previous year. During both February 1998 and 1999 Meuschenia trachylepis 20-30mm in size were caught but in very low abundance. 202 (A) (B) Otti*erl997 1—I—I—I I I 1 1—1—I—I—I—I—I—I 0 10 20 30 40 50 80 70 80 90 100 110 120 133 140 150 FehoaylSSS -I—I—I—I—I—I—I— -| 1 1 1 1 1 1 10 20 30 40 50 eo 70 90 100 110 ia) 130 140 150 April 1998 -1—I 1 1 1—I—I—I—I—I—I—I—I—I—I 10 20 X 40 50 eo 70 80 90 KX) 110 120 130 140 150 T 1 1 1 1 0 10 20 30406060708090 100110120130140150 Jdyl996 Folk length (mm) -1—I—I—I—I—r ni—I—I—I—I—I—I—I—I 10 20 30 40 so eo 70 80 90 100 110 120 130 140 150 Octoba'1998 50- Oilalla'l<)98 tanax —1 1 1 1 1 1 1 25-J 50 so 70 90 100 110 120 130 1« 1S0 FchTffliyl999 0- —1—1—I—1—r- -1—I—1—1 1 50 0 10 2m0 30 40 50 80 70 80 90 100 110 120 130 140 150 I I I 1 1 1 1 90 100 110 120 130 1<0 150 April 1999 1 1 1 1 1 1 1 1 \ 1 g) 0 10 20 30 40 50 60 70 80 90 10O 110 120 IX 140 150 -1 1 1 1 I I 1 90 100 110 120 130 140 160 mw Julyl999 01 1 1 ^ 1 1 1 1 1 1 1 1 1 1 0 10 20 X 40 X eo 70 eo 90 100 110 12D IX 140 IX —1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10 20 30 40 50 eo 70 eo 90 too 110 120 130 1« 150 Forte lB^0t (nn| October 19» I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ) 10 20 X 40 X X 70 X X IX 110 IX IX MO IX February 2000 -1 1—I—1 1—I 1 1—I 1—I—I—I—I—I 10 a X 40 X X TO X X IX 110 120 IX 140 IX April 2000 T 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 10 X X « X X 70 X X IX 110 IX IX 140 1X July 2000 T—I—I—r -1—I—I—I—I—1—I—I—I—I—I 10 X X 40 X X 70 X X IX 110 1X IX 140 IX Ftx1(lengai(mni^ Figure 5.13: (A) Size composition of Meuschenia trachylepis caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Lake Illawarra have been shown. 203 (A) (B) 150-| October 1997 75- October 1997 100- • I 1 ) 10 20 30 n 1 60 70 80 90 100 110 120 130 140 150 40 50 *i Kbnaryim 25- 0-t—^ffr ,5Qi) 10 20 3300 40 SO X 70 X X IX 110 IX 1X 140 IX Central —T" 1 —I 1— 1^ 1 —1— 1 1 1 1 1 1 1 50-|) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 A(nll999 25- ,50J) 10 X X 40 50 ffl 70 X X IX 110 IX IX 140 IX Upper 1 -1—T r—1 1 1 soi) 10 20 30 40 50 60 70 80 -r 100 110 120 130 140 150 90 Jiiyl99» 25- 0 10 X X 40 X X 70 X X IX 110 IX IX 140 IX Fc>1(len9lti(nTr) 1 1 1 _••1 _1 1 "~1 I 1 1 1 1 3 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 50- October 1998 25- 1" 1 I 1 1 I— 1 r 1 1 1 50-p 10 20 30 40 60 60 70 80 90 100 110 120 130 140 150 February 1999 25- Numbe i 1 • 1 " 1 1 1 50-p 10 20 30 40 50 60 70 eo 90 100 110 120 1» 140 160 A|xiI1999 25- -T— 1 —1 T- 1 1 sn-! 20 30 40 50 60 70 —^ 90 100 110 120 IM 140 160 ? ^° 80 July 1999 25- r r-—I— —I— 1 - 1 •T- 1 1 1 1 i~ 1 1 3 10 20 30 40 50 60 70 80 90 100 110 120 IM 140 150 50-| October 1999 25- 1 1 20 70 100 110 120 130 140 150 50-^ 10 30 40 50 60 80 90 July 1999 25- —I— 1 1— 1 —1— ~1— II 1 1 1 'i 50-ij 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 April 2000 25- —1— 50-S 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 July 2000 25- —1— I— 1 —r-—r-—1— n -1 1 1 1 1 C 10 20 30 40 50 80 90 60 70 100 110 120 130 140 150 Fork length (mm) Figure 5.14: (A) Size composition of Meuschenia trachylepis caught in St Georges Basin over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within St Georges Basin have been shown 204 Recruitment of Meuschenia trachylepis into Lake Conjola was evident in both October 1997 and 1998, but higher numbers were caught in 1998. No recruitment event was evident in October 1999 (Figure 5.15A). Recruitment was most evident at the central location, with only low number of the new recruits caught at the entrance (Figure 5.15B). Like other estuaries mentioned, the Meuschenia trachylepis caught in Febmary 1999 were large juveniles in the size range of 40-70mm. A low number of new recruits as well as juveniles were found in Febmary 2000 (Figure 5.15A). During the first year of sampling there was no large recmitment event detected by this study in Wallaga Lake, but individuals less than 40mm were caught on all sampling events, as well as larger juveniles (Figure 5.16A). A recruitment peak occurred in October 1998, and individuals 10-30mm in length were caught, surprisingly mostly at the upper location (Figure 5.16B). As was the case for the other three lakes, juveniles in the size range 60-120mm being caught in Wallaga Lake in Febmary 1999, and these were found at the central and upper location (Figure 5.16B). No other obvious recmitment events occurred with only larger individuals being caught (Figure 5.16A). 205 (A) (B) Q*terl997 T—I—r "T I I I I I I I I 10 20 30 40 50 60 70 80 90 103 110 120130140150 RbunylSSB October 1998 T 1 1 1 1 1 1 1 1 1 1 1 1 1 1 5^0 1QaD3040SDeQ7DaD90 10D110iaD13314Q15D April 1998 1—I—I—I—I—I—I—I—I—I 25- jpO0 10 20 » 4400 50 eo 70 83 90 1® 110 123 130 140 150 -I—I—I—I—I—I—I—I—I—I—I—I—I—I—I 504* 1OaDX4050eD7O8090ia)110ia)130140150 Ji^1998 0-1—^^^^- -I—I—I—I—I—I—I—I—I—I—I 50 0 10 20 30 « 50 60 70 80 90 100 110 120 130 140 150 -| 1 1 1 1 1 1 1 1 1 1 1 1 1—I 0 10 20X405060708090 100 110 120130140130 ICOn QUH-1998 33- 1—r^—1—I—I—I—I—I—!—I—I—I—I—I 0 10 20 X 40 50 60 70 80 90 100 110 123 130 140 150 -| 1 1 1 1 1 1 1—I 1—I 100-f 10 20 3D 40 30 60 70 80 90 100 110 12) 130 140 150 RliiBiyl999 I 50- E -1 P -I—I—I—I—I—r F*nBiy«99 3 0 10 20 M 40 30 eo 70 80 90 100 110 120 130 140 150 ^ 60-P ApdI1999 25- —1 1 1—I 1—I I I I I I I I I I I I I I I I -! 1 1 1 I I 1 T— igjj) 10 20 X 40 X ffl 70 X X IX 110 IX 130 140 IX 50-P 10 20304050607080 100 110 120 130 140 150 Julyl9!l» 25- I ' I I r-~i r-^i I r~T i i i i i -1—r 0 10 2D X 40 50 60 TO aD 90 m 110 120 130 140 153 3 10 20 X X40 X X TO « X 100 110 120 IX 140 IX ro- 3D- OddaerW) Vfpa 25J X- 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 p 10 aD X 40 53 60 70 X 90 100 110 120 IX 140 IX 1 1 1 1 1 1 1 1 1 1 n 1 1 1 1 S0-| D 10 20 X 40 50 60 70 80 90 100 110 120 130 140 150 Ktnay20tD Fort(Lfin9h(iTiT| 3- 0- 1 1 n 'i"~r 1 II x^P 10 2) X 40 X ffi 70 X X iro 110 IX IX 140 1X ^^2000 25- -1 1 1 1—I—I—I—I 1 1—I—1 1—I—I X. 10fflX4DfflffiTOffiX10D110 1X1X1401X MyWa 25- I I I I I I I I I I I I I I I 10 X X 40 X X 70 X X IX 110 120 IX 140 IX Rikki|)Ui(inT| Figure 5.15: (A) Size composition of Meuschenia trachylepis caught in Lake Conjola over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Lake Conjola have been shown 206 50-| (B) Ortoharl997 25- o4 1 1 " 10 20 30 40 50 60 70 X 90 IX 110 120 IX 140 IX 50-^ February 1998 50-, October 1998 fiOnux 25- 25- -I I 1 50-? 10 20 30 40 50 60 70 X 90 100 110 120 IX 140 IX 0- 1 April 1998 10 20 30 40 SO 80 70 80 90 100 110 120 130 140 ISO 25- 50- Cmtral 1 1 1 1 1 1 !•• 1 1 25- 50-j 10 20 30 40 50 60 70 X 90 IX 110 120 IX 140 IX July 1998 0- 1 -T" 1 100 110 120 IX 140 150 25- 50- 10 20 30 40 50 60 70 80 90 Upper 0- 1 ~l "• 1 1 1 1 1 1 1 1 1 ~T" ' 1 26- 0 10 20 X 40 50 X 70 X 90 IX 110 120 1X 140 IX 50-| October 1998^^^ 1 1 1 ' ' 1 1 25- 0 10 20 30 40 60 60 70 80 90 100 110 120 IX 140 150 0- 1 —1— —T" 1 n—1—1—1—1—1—I- 1 1 10 20 30 40 50 eo 70 50- X X IX 110 120 IX 140 IX 25- Fdbnmiyl999 RxklenE^(rm4 Numbe r 'H —I— 1 50 50- 3 10 20 30 40 50 X 70 X X IX 110 120 IX 140 IX ditnoce April 1999 25 25- FiElnBryl999 0- 0 ••— 1 1 —r- 1 i——I — 1 1 1 3 10 20 40 50 eo 70 X X IX 110 120 IX 140 IX 50 ) 10 23 40 60 60 70 80 90 IM 110 120 IX 140 IX 50- 30 July 1998 Central 25- 1 ^ 3 0- Z 1 1 1 1 1 ~i 1 1 1 1 1 1 1 1 1 3 10 20 30 40 50 70 X X iro 110 120 IX 140 IX eo ) 10 30 50 eo 70 80 90 IX 110 IX IX 140 IX 50 50 20 40 October 1999 Upper 25 25 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 50 20 X 40 X X 70 X X IX 110 120 IX 140 IX 1 1 J) 10 0 10 20 X 40 50 60 70 80 90 IX 110 IX IX 140 IX FdxuvylOOO RiKlenEfli(n>i4 25 0 1 T— r 1 —r —r —r 1 —1—r—i—I ~i— 1 r^ 50 0 10 X eo 70 20 40 SO X X IM 110 IX IX 140 IX 25 April 2000 0 1 1 1 1 1 1' 1 1 1 1 1 1 1 1 1 50 P 10 20 X 40 X X 70 X X IX 110 120 IX 140 IX July 2000 25 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 10 20 X 40 X X 70 X 90 100 110 120 IX 140 IX Fork length (mr^ Figure 5.16: (A) Size composition of Meuschenia trachylepis caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Wallaga Lake have been shown 207 5.3.5 Monacanthus chinensis (Osbeck 1765) Previous studies Monacanthus chinensis is a member of the Monacanthidae family of which there are approximately 60 species in Australian waters (Kuiter 1993). They inhabit a variety of habitats, from estuaries to inshore reefs at a depth of 5-50 metres, but are occasionally trawled much deeper (Kuiter 1993). Monacanthus chinensis is part of the Estuary General Fishery in NSW, but again it is not possible to determine catch rates as all leatherjacket species are combined in the available statistics. This is despite the fact that the leatherjacket species caught in the estuaries all have very different life history characteristics, habitat requirements and basic biology. Confidence in the stock assessment of leatherjacket populations is regarded as low (NSW Fisheries 2002) There is little information on reproductive behaviour available, but Monacanthus chinensis are known to spawn within estuaries. Hannan & Williams (1998) concluded that the main recruitment period on the central coast of NSW was from February to June. In Botany Bay (Sydney), recruitment was evident in February (SPCC 1981). 5.3.5.1 Discussion of Results A total of 311 individuals were caught in the seven estuaries. The highest abundance of Monacanthus chinensis was caught in Wallaga Lake, followed by St Georges Basin (Figure 5.17). Less than fifty individuals were caught in each of the remaining estuaries (See species 208 table, Chapter 3). Only three individuals were caught in Coila Lake and seven in Lake Illawarra. These latter estuaries will be excluded from further analyses. Patterns of Abundance of Monacanthus chinensis There was significant difference in the abundance of Monacanthus chinensis among locations and through time for St Georges Basin, Burrill Lake and Wallaga Lake (Table 5.2). For these estuaries, the interaction of site and time explained the largest amount of variation in the model, followed closely by time of sampling. The location factor contributed very little to explaining the variation in abundance of Monacanthus chinensis (Table 5.3). There appeared to be high variability in the strength of recruitment between years. No consistent differences in the abimdance of Monacanthus chinensis were found in Lake Conjola and Merimbula Lake (Table 5.2). For St Georges Basin, Burrill Lake and Wallaga Lake, there were differences among these estuaries in the timing of peak abundance, as well as where the greatest abundance was caught within the estuary (Figure 5.17). For example, in St Georges Basin, during the first year there were peaks during February, April and July the fish were caught at the entrance and central locations. In Burrill Lake, there was a peak only in July and October 1998 and these fish were caught at the entrance (Figure 5.17). Wallaga Lake was different again, as very few individuals were caught at the entrance and peaks occurred in February (Figure 5.17). 209 Lake Illawarra St Georges Basin - entrance - central upper -l^S>*B —«--'J-;=^* -m—m^i^m^^ o.c -m-^'i ii 53 H 2 B m-^»^ Lake Conjola Burrill Lake I 0.5- ' • • 1 * • « « a * a a .^S-n- . 2 Coila Lake WaUaga Lake 1 »—*—*--*-: *___.i_ M -• — *—*--*-• •---•—•—•—•—•—m i- m-^~^-m—• -T ; 1 1 1 10/972/98 4/98 7/9810/98 2/99 4/99 7/9910/99 2/00 4/00 7/00 10/97 2/98 4/98 7/9810/98 2/99 4/99 7/9910/99 2/00 4/00 7/00 Sampling Event Merimbula Lake .-1 • -- »- 10/97 2/98 4/98 7/9810/98 2/99 4/99 7/9910/99 2/00 4/00 7/00 Sampling Event Figure 5.17: Mean numbers of juvenile Monacanthus chinensis cqjtured at the entrance, central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled for two years. Data was log (x+1) transformed. Bars denote standard error. 210 Length Frequency of Monacanthus chinensis Detailed recruitment information will be limited to St Georges Basin and Wallaga Lake, due to the small catches at the other estuaries. Monacanthus chinensis appear to have a protracted recruitment period, and the timing of peak recruitment was different between these two estuaries. In St Georges Basin, the main recruitment period was from February to July with recruits less than 40mm in length caught during the sampling events of February, April and July 1998 (Figure 5.18a). However, the magnitude of recruitment during this period was quite variable between years (c.f,, April 1999, February and July 2000) (Figure 5.18a). The distribution of individuals within the estuary changed throughout time. During April 1998, small individuals (<30mm) were caught at the entrance, and larger juveniles (30-130mm) were caught at the upper location (Figure 5.18b). Pattems of distribution changed during the next sampling event with new recruits caught at the enfrance and central locations, but no juveniles caught at the upper location (Figure 5.18b). Wallaga Lake also had similar variability in the strength of recruitment between years, and recruitment was stronger in the first half of the study. New recruits were caught in the period from February to October in 1998 (Figure 5.19a). For the remainder of the study, new recruits were not found in the October sampling event. The peak recruitment period seemed to occur primarily in early February 1999, with a large number of Monacanthus chinensis 30-50mm caught at this time (Figure 5.19a). Individuals less than 40mm were also caught during February 2000, with a very small number caught in April 2000 (Figure 19a). Within Wallaga Lake, individuals were mainly caught at either the cenfral or upper locations (Figure 5.19b). 211 (A) (B) 20 Octoberl997 10- i«pai998 I I I I I I I I I I I I I I I p 10 20 X 40 X X 70 X X 1X 110 IX 1X 140 1X F*cuaryl99g 10- T—I—I—I—I—I—r IQJ) 10 20 X 40 X eo TO 80 X 100 110 120 IX 140 IX T-T- -l—l- 1 1 20-iS>i 10 20 X 40 X X 70 X X 1X 110 IX IX 140 IX Qllial i^l998 —I—I—I—I—I—I—I—I—I—I—I—I—I—I—I -1 (—I I—I 1 1 10 2D X 40 a 60 70 X X IX 110 IX IX 140 IX X X 70 X X ix 110 IX IX 140 ia 10-P July 1998 10- 0 -1 1 I I I I 1 1 1 1 1 1 1 1—I 0 10 X X 40 X ffl 70 X X IX 110 IX 1X 140 IX 0 10 X X 40 X 60 70 X X IX 110 IX IX 140 IX Fi3klen^(nTTi) Cfctoberl -1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 p 10 X X 40 X X 70 X M IX 110 1X IX 140 1M My 1998 I Febniaiy 1999 -1—I—I—r —\ 1 1 1 1 1 ^ 1 1 1 P 10 20 X 40 X X 70 X X IX 110 120 1X 140 IX -|—I—I—I—I—I April 1999 ,0i) 10 X X 40 X X 70 X X IX 110 IX IX 140 IX Gxtral -1 r -1 1 1 1 1 1 1 1 1 1 2oi) 10 X X 40 X X 70 X X IX 110 1X IX 140 IX July 1999 fQjf 10 X X 40 X ffi 70 X X IX 110 IX IX 140 IX 10- 0 -1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 10 X X 40 X X 70 X X IX 110 IX IX 140 IX X October 1999 —1—I—I—I—I—I—I—I—I 10 0 10 X X 40 X 70 X X IX 110 IX IX 140 IX Fbrt -I—I—I—r- -1—I—I—I—I—I—I—I—I—I—I p 10 X X 40 X X 70 X X IX 110 IX IX 140 IX April 2000 ~\ 1 1 1— -1 1 1 1 1 1 1 1 1 1 1 x-V 10 X X 40 X X 70 X X IX 110 1X IX 140 IX July 2000 10 0 -| l~~l \ 1 1 1 1 1 1 1 1 1 1 1 0 10 X X 40 X X 70 X X IX 110 IX 1X 140 IX Folk tefigth (imf Figure 5.18: (A) Length of Monacanthus chinensis caught in St Georges Basin during each sampling event, (B) Distribution of individuals at peak recruitment times at the entrance, central and upper locations. 212 (A) (B) 20 October 1997 10- 0 —1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 20 J? 10 20 30 40 X 60 70 X X IM 110 120 IX 140 IX Fdituaiy 1998 10 0 T- -P 1—1 r 20^ 10 20 30 40 X X 70 80 X IX 110 IX IX 140 IX April 1998 10- 0 -1 1 1 1 1 1 1 1 1 20-9 10 X 30 40 X X 70 M X 1X 110 IX IX 140 IX July 1998 Fehmaiyl999 -i 1 1 1 1 1 1 1 1 10 20 30 40 X 60 70 80 X IX 110 IX 130 140 IX 20- October 1998 0> -]—I—I—I—I—I—I—I—I—I—I—I—I—I—I .a 10- 2oJ) 10 20 X 40 X X 70 80 X IX 110 IX IX 140 IX E 3 -1 1 1 1 1 1 1 1 1 1 1 1 Z 10 20 X 40 50 X 70 X X IM 110 120 IX 140 IX 20-V February 1999 10- 2oil 10 20 X 40 X X 70 X X IX 110 IX IX 140 IX -| 1 1 1 1 1 1 10 20 X 40 M X 70 X X IM 110 120 IX 140 IX i^ll999 1 1 1 1 I I 1 i 1 1 1 1 1 1 1 0 10 X X 40 X X 70 X X IX 110 IX IX 140 IX 0- -I—I—I—I—I—I—I—r~T—I—I—I—I—I—I Fccklen£^(nn4 X- 10 » X 40 X X 70 X » 100 110 120 IM 140 IX July 1999 10- 0 -1—I—I—I—I—I—I—I—I—I—i~n—I—I—I 0 10 X X 40 X X 70 X X IM 110 120 IX 140 IX 20-, Octoba-1999 Fetiuaiy2000 10- 0 —1 1 1 1 1 1^ 1 1 1 ^ 1 1 204" 10 20 X 40 X X 70 X X 1X 110 IX IX 140 IX I—I—I—r~i—I—I—I—I—I—I—I—I—I—I February 2000 ,oil 10 X X 40 X X 70 80 X IX 110 IX IX 140 IX 0 -1 1 1 1 1 1 1 1 20-9 10 X X 40 X X 70 80 X IX 110 IX 1X 140 IX y^ril2000 ^—I—n~i—I—I—I—I—I—I—I—i—I—I 1Qi> 10 X X 40 X X 73 X X IX 110 IX IX 140 IX LfepCT 0 I 'I n—I—I—T"^—^—I—I—I 20-' 10 20 X 40 X X 70 80 X IM 110 1X 1X 140 IX July 2000 10- 1—I—I—I—I—I—I—I 0 10 X X 40 X X 70 80 X IX 110 IX IX 140 IX 0 —[ 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Forkleng»i(nn]| 10 20 X 40 X X 70 80 X IM 110 120 1X 140 IX R>rk Lengtti (mm) Figure 5.19: (A) Size composition of Monacanthus chinensis caught in Wallaga Lake over the three- year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Wallaga Lake have been shown 213 5.3.6 Gerres subfasciatus (Gunther 1859) Previous studies Gerres subfasciatus belong to the Gerreidae family, and are a small silvery species of fish inhabiting estuaries, shallow coastal waters and sandy habitats over reefs (Kuiter 1993). They are distributed in temperate waters between central NSW and southem Westem Ausfralia (Kailola et al. 1993). Gerres subfasciatus are harvested by commercial fishes, mainly in NSW, using beach seine nets in inshore waters. Approximately 100-176 tonnes a year are harvested (Kailola et al 1993). Gerres subfasciatus are thought to be estuary spawners. The main recruitment period for Gerres subfasciatus in Botany Bay (Sydney) was from Febmary to April, and the species was caught in shallow waters at approximately 5-24mm long (SPCC 1981). In Lake Macquarie on the cenfral coast of NSW, the main recmitment period was from Febmary to August (Hannan & Williams 1998). 5.3.6.1 Discussion of Results The highest number of Gerres subfasciatus was caught in Lake Illawarra, with similar numbers caught in Lake Conjola and Wallaga Lake (Table 5.1). Less than one hundred individuals were caught m Merimbula Lake and Burrill Lake, while in St Georges Basin and Coila Lake no Gerres subfasciatus were caught at all over the three year sampling period (Figure 5.20). St Georges Basin and Coila Lake have been excluded from further analyses. 214 Patterns of Abundance of Gerres subfasciatus There was considerable spatial and temporal variation in the abvmdance of Gerres subfasciatus between locations and throughout time for Lake Illawarra, Lake Conjola and Merimbula Lake (Table 5.2). There was no significant differences among sites and time for Wallaga Lake and Burrill Lake (Table 5.2). Length Frequency of Gerres subfasciatus Discussion of recmitment events and size distributions will be limited to Lake Illawarra, Lake Conjola and Wallaga Lake. Overall, the recmitment period for Gerres subfasciatus in south- eastem Ausfralia appears to occur from Febmary to July, with a recmitment peak in April. Within Lake Illawarra, newly-settled Gerres subfasciatus less than 40mm in length were caught in high abundance during the months of Febmary and April, with weaker recmitment extending into July (Figure 5.21a). Larger juveniles of a size 30-90mm were caught in the month of October, suggesting that recmitment may extend into August/September (Figure 5.21a). Recmitment was particularly sfrong during Febmary 1998, and new recmits were exclusively caught at the upper location of Lake Illawarra (Figure 5.21b). The distribution of Gerres subfasciatus was not as constrained during April 1999, when recmits were found at the cenfral and upper locations (Figure 5.2IB). 215 1.8-, Lake Illawarra St Georges Basin -entrance central jk upper 1.2- 1 • • • 0.6- / \ •Vl ! A \ A 4 A • / 4 • * 0.0- • "•-• » m - m 1— I 1 1 1— 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2^8 4/98 7/98 10/98 2/99 4/98 7/99 10/99 2/00 4/00 7/00 Lake Conjola Burrill Late 3 0.6 c s . + »t s J H i s t -T 1 r- —T 1 r~ 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/09 10/99 2/00 4/00 7/DO 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Coila Lake Wallaga Lake 1.2- • 0.6- /'• • * * 0.0- • m- it * 1 . ! * 1 1 r— 10/97 2/98 4/98 7/98 10/96 2/99 4/99 7/99 10/99 2/00 4/00 7/00 10/97 2/98 4/98 7/98 10/98 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Event Merimbula Lake 1.2- A. 0.6- • A 0.0- a • * m 1 1 —1— —I— —1—1 10/97 2/96 4/98 7/98 10/96 2/99 4/99 7/99 10/99 2/00 4/00 7/00 Sampling Event Figure 5.20: Mean munbers of juvenile Gerres subfasciatus captured at the entrance, central and upper locations of the six estuaries sampled quarterly over three years, and for Merimbula Lake which was sampled quarterly for two years. Data was log (x+1) transformed. Bars denote standard error. 216 (A) (B) 80 Ti Oi*obarl997 40- I I r I I I—I—I—I—I—I 80 .•?) 10 2^0 40 50 60 70 80 90 100 110 120 130 140 150 F«hruaiyl999 40 Febniaiy 1998 • —\ I I I I 1 I I I 1 I goJj) 10 20 30 40 50 60 70 80 90 ICO 110 120 130 140 150 —1—I—I 1—r—1—I—1—I—I—I 1 1 1—I April 1998 10 20 30 40 50 60 70 80 90 100 110 120 IX 140 160 40 Central -r ^ "I 1 1 1 1 1 1 1 1 1 1 gQ 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 J«yl998 40- 30^1 10 2^0 44<0 50 60 70 80 90 100 110 120 130 140 160 l*!W -1 1 1—1- T 1 1 1 1 1 1 1 1 1 1 0 10 20 X 40 50 60 70 80 90 100 110 120 IX 140 150 80' October 1998 O-l ^^^W T 1 1 1 1 1 1 1 1 1 Ji 40- 0 10 20 30 40 60 60 70 80 90 100 110 120 130 140 160 E Forte length (mrj) Z 0 —I 1 f- I I I I I 1 1 1 1 1 1 80.0 10 20 X 40 50 60 70 80 90 100 110 120 1X 140 ISO Februaiyl999 T 1 1 1 1 1 1 1 1 1 Asriim 60 60 70 80 90 100 110 120 130 140 150 Eetnace Aprill999 ^tm —1 I I I 1 I I I I I I I I I I 50 60 70 80 90 100 110 120 IX 140 150 ajj) 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 July 1999 Gontral —1 1 1 1 1 1 1 1 1 1 1 10 20 X 40 X X 70 X X IM 110 1X IX 140 IX I I I I I I I I I X- 20-P 10 20 X 40 50 60 70 80 90 100 110 120 130 140 150 October 1999 40- l*I»r P[ p^ r !•• —i— —I— —I— 1 floJ X X 40 30 X 70 X X T 1 ^^^^"1- -1—I—I—I—I—I 1—I—I—I IX 110 IX IX 140 IX Fd)ruiiry2(IQ0 0 10 20 X 40 50 60 70 80 X 100 110 120 IX 140 150 40- Fork length (rrrrj) 0- 1 —r- 1 -T- 1 1 1 1 1 1 X- j) 10 X X 40 X X 70 X X IX 110 IX IX 140 IX April 2000 40- •• I •1~ "T" "T- "T— 1 1" 1 1 1 1 1 j) 10 X X 40 X X 70 X —r-1X 110 IX IX 140 IX x-j X MyUm 40- 0- —i— -m-—r- 1 1 1 —I 1 1 1 1 1 0 10 X X 40 X X 70 X X IX 110 IX IX 140 IX ForkL£nc|th(inrj| Figure 5.21: (A) Size composition of Gerres subfasciatus caught in Lake Illawarra over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Lake Illawarra have been shown. 217 The strength of recruitment of Gerres subfasciatus into Lake Conjola varied considerably through time, with one major recruitment event recorded for April 1999 (Figure 5.22a). Very few individuals were caught diuing the first six sampling events, but after April 1999, low numbers of individuals, ranging from 10-50mm in length, were caught during the remainder of the study (Figure 5.22a). Like Lake Illawarra, newly-settled recruits of Gerres subfasciatus in Lake Conjola were concentrated at the central and upper locations (Figure 5.22b). Wallaga Lake also showed considerable temporal variation among years in the abundance of Gerres subfasciatus. Recruitment was apparent from February to July but was relatively weak (Figure 5.23a). A high abundance of Gerres subfasciatus was caught during April 1998, and the majority of the small individuals 10-30mm in length were caught at the entrance location, with lower numbers caught at the central and upper locations (Figure 5.23b). 218 (A) (B) XT Octoberl997 40 20- 0 —1 l~~l 1 1 1 1 1 1 1 1 1 1 1 1 X-^ 10 20 X 40 X X 70 X X IX 110 IX IX 140 1X 40 February 1998 20- 0 —1 1 1 1 1 1 1 1 I I 1 1 1 1 1 xJ? 10 20 X 40 X X 70 M X IX 110 120 IX 140 IX 40 April 1998 X- 0 —I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 x:? 10 X X 40 X X 70 X X IX 110 120 IX 140 IX 40- July 1998 20 0 —1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10 20 X 40 X X 70 M X IX 110 120 1X 140 IX X- October 1998 X- ApAWi 0 —1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 x-? 10 X X 40 X X 70 X X IX 110 1X IX 140 1X BUrance February 1999 M XH E 3 —I—I—I—1—I—I—I—I—I—I—I—I—I—I—I 10 30 X 40 50 60 70 80 90 100 110 120 IX 140 150 Z X0 0 10 X X 40 X X 70 X X IX 110 IX IX 140 IX Aprill999 Gstial 0 ^ 1 1 1 1 1 1 1 1 1 1 1 X .1 10 X X 40 X X 70 X X IX 110 IX IX 140 IX O-l—r~^^^- —I—I—I—I—I—I—I—I—I g, 0 10 a X 4400 X 60 70 X X lOD 110 120 IX 140 IX July 1999 X- IhB- —1—I—1 1 r "1—1 •••-1—1 '-r r—1 X- October 1999 o-l—^^W- 1—I—I—I—I—I—1—I—I—1 0 10 X X 40 X a 70 X X IX 110 120 IX 140 ia X- Rj1 0 I I I I I I I I I I I I X-f 10 X X 40 X X 70 X X IX 110 IX IX 140 IX April 2000 X- -1 1 I I I 1 1 1 1 1 1 1 1 1 1 60il 10 X X 40 X X 70 X X IX 110 IX IX 140 IX July20Q0 X- —1—r~T—I—I—I—I—I—I—I—I—I—I—i—1 0 10 X X 40 X X 70 X X 1X 110 1X IX 140 IX Fork length (inn) Figure 5.22: (A) Size composition of Gerres subfasciatus caught in Lake Conjola over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Lake Conjola have been shown. 219 (A) X (B) October 1997 25H 0 —I—I—I—I I I—r~—I—I—I—I—I—I—I—I X-!? 10 X X 40 X X 70 X X IX 110 IX IX 140 IX Febniaiy 1998 25- A|ill99B 0 I I I i I I I I 1 I I I I I I EMmce X-? 10 X X 40 X X 70 X X IX 110 IX IX 140 IX April 1998 25 0 T 1— oj—^W- T—I—I—I—I—I—I—I—I—I—I—I ^ 10 20 X 40 X X TO 83 X tOD 110 120 IX 140 160 X-? 10 X X 40 X 70 X X 1X 110 1X 1X 140 1X July 1998 Osini Si 20- E —I 1 I I 1 r—1 1 1 1—1 1 1 1—I 3 10 X X 40 X X 70 X X 1X 110 IX IX 140 IX 1—I—I—I—1—I—I—I—I—I—I—I 4QO 10 20 X 40 X 60 TO ffi X 100 110 130 IX 140 ia Ocotberl998 Vppar 10 X X 40 X X 70 X X 1X 110 IX 1X 140 IX I I I I—I—I—I—I—I—I—I—I February 1999 0 10 a X 40 ffi ffl 70 ffi X IX 110 120 IX 140 1X FaklerQ^(mT) I I I 1 1 1 1 1 1 1 1 1 1 1 1 10 X X 40 X X 70 X X IX 110 IX IX 140 IX April 1999 —^ 1 1 1 1 1 1 1 1 1 1 1 1 10 X X 40 M X 70 X X IX 110 IX 1X 140 IX July 1999 "1 I 1 1 1 1 1 1 1 1 1 1 10 20 X 40 X X 70 X X IX 110 IX 1X 140 IX October 1999 —1—r~T—I—I—I—I—I—I—I—I—1—I—I—I 10 X X 40 X X 70 80 X IX 110 IX IX 140 IM February 2000 25- 0 —1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 X-9 10 X X 40 X X 70 80 X IX 110 IX IX 140 IX April 2000 25- 0 —I 1 1 1 1 1 1 l~~I ^~1 1 1 1 1 X-? 10 X X 40 X X 70 X X IX 110 IX IX 140 IX July 2000 25 • 0- —1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10 X X 40 X X 70 X X IX 110 IX IX 140 1X RMIC length (mm) Figure 5.23: (A) Size composition of Gerres subfasciatus caught in Wallaga Lake over the three-year period, separated into the twelve sampling events. (B) For peak recruitment events distribution of individuals among locations within Wallaga Lake have been shown. 220 5.4 Conclusion 5.4.1 Major findings This study represents the first comprehensive multi-scale analysis of the recruitment of commercially and recreationally important fish species south of the Sydney Basin. It has also provided detailed information on how intermittently open and closed lakes and lagoons in the southeast region of NSW are utilised as nursery habitats by many marine and estuarine spawning fish. The major findings of this study were: firstly, that there was a substantial increase in the strength of recruitment in 1998 compared to the other two years that were sampled, and that this was evident for each of the selected species and across all estuaries; secondly, that there were no consistent sites of recmitment, and pattems of settlement for all species at the three locations within the estuaries exhibited large variability through time; and lastly, that there were regional differences in the timing and magnitude of recmitment in the seven estuaries along a latitudinal scale. 5.4.2 Summary of spatio-temporal patterns in recruitment events For the south-east coast of NSW, the species examined here had protracted recmitment periods, with timing consistent with previous observations for locations of central NSW. Some of the species exhibited latitudinal differences in the timing of peak recmitment events (Table 5.4). In summary, a general recmitment period for Acanthopagrus australis occurred during spring/summer (September/October to Febmary). This however was not consistent 221 Table 5.4: Principal recruitment periods for five fish species caught in six estuaries of southeast Australia, over a three-year period, and Merimbula Lake that was sampled for two years. Species Principal Recruitment Time Acanthopagrus Inconsistent among estuaries australis Lake Illawarra to Burrill Lake: September / October to February. Also July 2000 Coila Lake: governed by entrance opening. October & April Wallaga Lake: April to October Girella Lake Illawarra: Inconsistent among years. 1997 &1998: October tricuspidata 1999: February and April St Georges Basin: October to February Wallaga Lake: October to April Merimbula Lake: February Meuschenia Strength inconsistent among years trachylepis October, and extending to December Monacanthus Protracted season. Variable among & within estuaries chinensis St Georges Basin: February to July Wallaga Lake: February. October 1997 only Gerres February to August, with a peak in April subfasciatus None caught in St Georges Basin & Coila Lake across all estuaries. In Wallaga Lake the recmitment period was more prominent in the period April to October. The timing of recmitment of Girella tricuspidata along the south-east coast of NSW generally appeared to occur from October to Febmary, but the strength and timing varied with latitude. In Wallaga Lake it extended fi-om October to April, and in Merimbula Lake strong recmitment of Acanthopagrus australis occurred only during Febmary. Meuschenia trachylepis recruitment appeared to occur during October, and extended to December. Monacanthus chinensis appeared to have a protracted recmitment period in the 222 south coast estuaries and the timing of peak recmitment is different among the estuaries. In St Georges Basin, the main recmitment period was fi-om Febmary to July, but the magnitude of this recmitment was quite variable within this period among years. Wallaga Lake also had similar variability in the strength of recmitment among years but the peak recmitment period appears to occur primarily in early Febmary. Overall, the recmitment period of Gerres subfasciatus in the estuaries of south-eastem Australia appears to occur from Febmary to July, with a recmitment peak in April (Table 5.4). 5.4.3 Temporal patterns in recruitment There was considerable variation in the magnitude of recmitment between years for all species. The most significant finding was the large and significant increase in recmitment during spring/summer 1998/99, compared to the relatively weak recmitment events in the other years. Recmitment was particularly strong in October 1998. Importantly, this major increase in recmitment was evident across all ICOLLs, and for most species. This suggests that there had to be widespread processes occurring to cause changes on a regional scale. It is likely that extemal factors, such as climatic cues, may have influenced recmitment dynamics along the whole SE Australian coastline during this study period. Changing weather pattems such as rainfall, wind speed and wind direction have all been suggested as a spawning cue for adult fish (SPCC 1981; Smith 1999). On a larger scale, the El Nino events which cause decreased rainfall, cooling of sea temperatures and decrease in trade winds, has been linked to causing major changes in some fisheries in the Pacific region. The most well-known example is the Pemvian anchovy fishery (Lee & Pritchard 1996). The impacts of El Nino events and climate regime shift on fisheries resources and marine 223 ecosystems has been investigated though in many countries, particularly for the East China Sea, Japan sea and parts of the Pacific Ocean (Chavez et al 1999; Godinez-Dominquez et al 2000; Sugimoto et al 2001). Major changes in recmitment strength have been foimd as well as, a shifting or spreading of spawning grounds of marine species, and changes in fish community stmcture, through successive recmitment failure or success of some species (Kimura et al 1997; Lu et al 1998; Sanchez-Velaso et al. 2000). Also there are complex ecological and food web interactions, such as changes in chlorophyll concentrations and plankton biomass with El Nino cycles (Sugimoto et al 2001). In respect to estuaries, there has been research showing that the El Nino southem oscillation phenomenon influences precipitation and estuarine salinity, and thus has a strong influence on recmitment, immigration and emigration of fish species within and adjacent to estuarine habitats (Vera & Sanchez 1997; Swales et al 1999; Garcia et al 2001). In Australia, there has been little investigation of the link between El Nino cycles and recmitment dynamics of marine fish species, even though great attention is given to the terrestrial effects of El Nino (e.g., Howden et al 1999; Jones & Trewin 2000; Potgieter et al 2002). Analyses have shown that decreased rainfall in Australia tends to be associated with El Nino, and in eastem Australia dry conditions predominantly occur in winter, spring and early summer (Chiew e? a/. 1998). Ocean conditions also change during El Nino events. In south east Australia the onshore transport of surface ocean water is favoured during El Nino, while in anti- El Nino events (La Nina) ocean upwellings could be expected to be more common (Lee & Pritchard 1996). The last El Nino event occurred in 1997/98, with a highly negative Southem Oscillation Index, lasting from January 1997 to approximately April 1998. The impacts arising from this El Nino event were below average rainfall totals on eastem NSW, 224 followed by consistently above average rainfall after April 1998 (Bureau of Meteorology 2002). Rainfall data for the south coast of NSW shows that the monthly average precipitation in August 1998 was the highest for the three-year period from January 1997 to January 2001, for all areas along the south coast from Wollongong to Merimbula (Appendix 1). In the Illawarra region the rains during this period caused a massive flooding event. Not only was the August 1998 the highest rainfall event, but the period from May to September in 1998 was on average four times higher than the previous year, and the volume of rain decreased even lower during this period the following year (Appendix 1). In fact, the 1997/98 El Nino has been regarded as the strongest on record (McPhadden 1999), and research of oceanic and atmospheric anomalies in the northeast Pacific ocean during the 1997/98 El Nino, suggest that a decadal climate shift may have occurred in late 1998 (Schwing et al. 2002). In this study, the consistent peak in recmitment in 1998 across the majority of commercial species and at most locations would seem to be linked to the increased rainfall recorded for that period, and possibly to other biological and ecological effects associated with El Nino events. The latter might include the increase in nutrients and in primary production. Large increases in rainfall and flooding events would cause flushing of the small tributaries into the ICOLLs, resulting in entrance openings and/or wider entrances than normally occurs. Most studies that have investigated increased rainfall and fish populations have mainly noted a decrease in recmitment or fish species diversity and abimdance. For example, Garcia et al. (2001) found that increased rainfall and high river discharge were associated with low abundance of marine species, and a decline in dominant euryhaline species, but the diversity and range of freshwater species increased. This was mostly due to increase in freshwater 225 flows lowering the salinity of estuaries and rivers, and thus creating unfavourable conditions for stenohaline species. However, in the present study, the increase in rainfall caused only a slight decrease in salinity (see Chapter 3, Figure 3.4). This may be due to the fact that the freshwater systems entering these ICOLLs are small tributaries and creeks, and the relative volume of freshwater entering the estuaries would be small. Also the immigration and retention of small juveniles within these systems could be related to the dominant winds at that time that favoured the onshore transport of larvae (see Chapter 6). It would therefore seem that spawning events and an increase in recmitment in this region may be largely governed by climatic variables, particularly high rainfall and flooding events. Most marine populations are characterised by large fluctuations in the magnitude of recmitment among years, but the results of this study suggest that fluctuations in recmitment on a broad community scale are related to rainfall cycles occurring over several years, possibly linked to El Nino events. How this affects long-term recmitment dynamics of marine and estuarine fish species in eastem Ausfralian waters is largely unknown, but it is reasonable to suggest that impacts would be numerable. Furthermore, the climatic situation in southem NSW is different to the rainfall cycles experienced on the north coast of NSW, where there is a greater amount of rain that is more consistent between years. Recmitment dynamics of fish communities into estuaries of southem NSW may be influenced by rainfall and climatic variables to a greater degree than in the north of the state. This may result in a greater degree of uncertainty in the strength of recmitment over long time frames, and such factors must be evaluated for fiiture fisheries management along southeast Australia. 226 It is quite likely that a strong recmitment events can sustain fishery catches in the following years, but the linkage of recmitment to subsequent adult numbers is often far from being clear. The relationship between a fishable stock and recmitment variability has long been a part of traditional fisheries management, in order to determine numerical harvest levels. The strong recmitment event detected by this sampling program gives an indication that monitoring recmitment into seagrass beds may be beneficial to understanding subsequent adult numbers. For example, Virgona et al. (1998) has suggested very high catches of sea mullet in NSW during the mid-1990s may have been facilitated by strong recmitment by the 1990-year class. It has been suggested that high catches of sea mullet, followed by years of declining catch and the average age of catch, are a reflection of recmitment and subsequent mortality of a strong year class in the fishery (Virgona et al. 1998). The strong recmitment of commercial fish across all estuaries in this study during 1998/99 may see favourable catches in fiiture years, and actually sustain the fisheries in this region for many years. Conversely, the relatively weak magnitude that was detected for other years may be part of the natural fluctuation of recmitment typical of fish populations, or more significantly be an early waming of recmitment failure of particular species. In this sense, this information could be a good indicator of recmitment strength of particular year classes, and be beneficial for the sustainable management of fisheries. Similarly, the information conceming differences in the consistency and strength of recmitment among estuaries is relevant to species that are known to have strong variations in year class strength between estuaries. For example, for Acanthopagrus australis there are indications of significant spatial variation in the relative abundance of different year classes of bream throughout NSW, suggesting recmitment to the Acanthopagrus australis fishery varies 227 substantially along the coast and through time (Gray et al 2000). Thus for those estuaries where consistent catches of newly-recmited Acanthopagrus australis were made, such as Lake Illawarra and Wallaga Lake, it is possible that these estuaries might be contributing to the fishery at a higher level than other estuaries along the south coast, and hence protection of their nursery habitats would be beneficial to the fishery. Unfortunately, the tme test of the relevance of recmitment information will only be known when these individuals are of a fishable age and size, and are regarded in fishery stock assessments. This highlights that well- replicated sampling programmes providing lengthy time-series data are needed to determine the importance of recmitment processes to adult numbers. 5.4.4 Spatial patterns of settlement within estuaries While there was some noticeable concurrent recmitment events across the seven estuaries (i.e., October 1998 event), the distribution of postlarvae and juveniles within the estuaries revealed a complex situation. The sfrength and timing of recmitment for all species differed considerably among the estuaries. The results were characterised by large and inconsistent differences in abundance, not only between the estuaries but also within them. Such intra- and inter estuary differences in abundance have been found in other studies of seagrass associated fish (Ferrell et al 1993; Gray et al 1996). Inconsistent pattems in the distribution of postlarvae throughout the estuaries were found for all species studied. At the spatial scale of locations within estuaries, uniform changes in abundance at the three locations within estuaries were rare. Differences in abundance were found between sites, indicating spatial variation in fish abundance at a scale of 10-20km, but these differences were small compared to the differences m abundance found throughout time. For these ICOLLs, there was an 228 ahnost complete lack of consistency in the sites of peak recmitment. This information is quite important for the management of these estuaries, where significant nursery areas and consistent sites of recmitment, particularly of those species exploited by commercial fisheries, have been advocated as priority sites for conservation. In many estuaries, where there were distinct pattems of settlement of ocean-spawning species and lagoon spawning species along the estuarine gradient, delineation of protection zones is a relatively easy process. For example, Hannan & Williams (1998) advocated that the entrance region of Lake Macquarie (NSW), should receive priority in protection due to the concentration of recmits of ocean-spawning individuals. The present study has shown that the enfrance sites are not always the main areas for recmitment, that other locations may be equally important nursery areas, and that it is virtually impossible to predict where peak abundance might occur within an ICOLL. This is especially tme when all species are included as pattems of distribution exhibit great spatial and temporal complexity. Bell et al. (1988) proposed that zone effects in the recmitment of individuals are likely to vary among estuaries. In the case of these ICOLLs, the influence of distance from the estuary mouth on fish recmitment could depend on their shape and morphology. In shallow estuaries, wind dfrection and velocity may be the major influences on estuarine circulation and hence larval supply within the estuary. These ICOLLs are small (10-40km^), and thus while there is not strong tidal movements within these estuaries, it seems feasible that water movements within the estuaries could transport these individuals 10-20 km away from the entrance region. Where currents are directed into the estuary during flood tide, coupled with wind forcing and residual circulation may result in larval transportation beyond the entrance. Wind-driven 229 surface currents would also exert a greater influence on those larvae that are surface- swimmers, such as Girella tricuspidata, Acanthopagrus australis and Rhabdosargus sarba (Tmski in prep.). There is also increasing evidence to suggest that larvae are not passive to water current movements but are actually capable and fast swimmers, able to travel long distances (Leis & Carson-Ewart 1997; Stobutzki & Bellwood 1997; Leis & Carson-Ewart 2001). Average swimming speeds recorded for temperate estuarine species in Lake Macquarie were 6.4 cm.s"^ for Acanthopagrus australis and Rhabdosargus sarba, 12.5cm.*' for Girella tricuspidata, and 10.9 cm.^'^ for Chrysophrys auratus (Tmski in prep.). While temperate larvae are much slower than tropical larvae (Leis 2002), such swimming ability redefines ideas of larval dispersal and retention. Other reasons why the entrance region was not always highly utilised may be due to the changing dynamics of this area. These estuaries are periodically open and closed to the ocean and thus the direct impact of currents and tidal movements is a changing one, making this area susceptible to environmental/physical change. This is particularly tme when they are opened by human intervention and not on a natural cycle. 5.4.5 Regional differences in recruitment Regional differences in abundances of commercially important species occurred in two different ways. The obvious one was difference in the strength of recmitment along a latitudinal scale, where in some instances recmitment of some species was not detected further south. For example, differences in recmitment among the estuaries occurred in July 2000, where recmitment of Acanthopagrus australis was found for Lake Illawarra, St Georges Basin, Lake Conjola and Burrill Lake, but not for Coila Lake, Wallaga Lake and Merimbula 230 Lake. Mechanisms contributing to this spatial variation were not investigated in this study, but several mechanisms are possible. This regional cut-off in the recmitment of individuals in the far south of the state could be a result of variability in the strength of the East Australian Current (EAC) throughout the year. For many species of economic importance, the EAC is the main fransport mechanism of larvae from migratory spawning mns. These results suggest that estuaries in southem NSW may be subject to a higher degree of uncertainty in the timing of recmitment, depending on the sfrength of the EAC. The second regional difference was that recmitment of some species was not detected in one or more estuaries but these species were caught in adjacent estuaries. This notable absence of some species in particular estuaries has been reported elsewhere (McNeill et al 1992b; Ferrell et al 1993; Gray et al 1996), and could be due to several factors. Spatial pattems in recmitment may arise due to variability in larval supply to different areas. For example, high recmitment may occur in areas where oceanographic features such as eddies concentrate larvae into an area, whereas low recraitment may be the result of a recmitment shadow where the area is down current (Bell & Westoby 1986b). Thus for estuaries such as St Georges Basin and Burrill Lake where typically low numbers of commercial species were found, it may be the result of larval supply via oceanographic transport and/or losses due to post- settlement mortality. It was also interesting that catches of some species were poor in some estuaries. For example, catches of Acanthopagrus australis were particularly poor in St Georges Basin, Burrill Lake and Merimbula Lake. The peak recmitment event of October 1998 was evident in these lakes, but for the majority of the other sampling events no bream were caught. Reasons for low catches are unclear as good numbers of Acanthopagrus australis were caught in estuaries near them at the same time. The EAC becomes increasingly 231 erratic in current movements and eddies as it travels south, and it may be possible that these estuaries are located in a region of the coastline where larval fish essentially by-pass the entrance mouth. Small-scale hydrological features may influence the supply of larvae arriving at a patch (Kingsford et al 1991). Oceanographic features such as eddies and currents have been suggested to influence the degree of recmitment to estuarine environments elsewhere (McNeill et al. 1992b). Other physical features such as wind forcing interacting with the coastline topography and orientation of inlet sources can produce spatio-temporal variation in larval supply to potential nursery habitats (Xie & Eggleston 1999). The results of this study also highlighted the transient nature of recmitment in fish populations and low catches may be the result of recmitment failure of a species at a given location or in a particular estuary. While the sampling in this study did have its limitations on a spatial and temporal scale, it covered the time between June and November, a period when recmitment of juvenile fish was expected (Middleton et al. 1984). Growth and emigration from the habitat following recmitment may be rapid enough for important changes to be missed by this quarterly sampling schedule. For example the recmitment of some species, such as Girella tricuspidata may have occurred between quarterly samples (Worthington et al 1992b). Recmitment processes changed over the three-year period in the strength and degree of patchiness. For some species, the major flooding event in the second year appeared to encourage a protracted period of recmitment. During the thfrd year of sampling a decrease in the number of Acanthopagrus australis was evident across all estuaries, with a notable total absence from some of the lakes. Despite low numbers, there were differences in the recmitment of Acanthopagrus australis among the estuaries. For Wallaga Lake and Coila Lake, there was a major recmitment event in April 1999. While small numbers of 232 Acanthopagrus australis were caught in Lake Illawarra and Lake Conjola at this time, the majority of these individuals were in the larger size classes and no Acanthopagrus australis were caught in St Georges Basin and Burrill Lake. In comparison, several hundred individuals in the size range 10-30 mm were caught in Wallaga Lake and Coila Lake, indicating they were new recmits. This suggests that this recmitment event is probably the result of a local spawning event and not a migratory spawning event. While there is supporting evidence that Acanthopagrus australis do participate in spawning runs (West 1993), there is also evidence suggesting that spawning Acanthopagrus australis may only move outside the estuary (Kesteven & Serventy 1941; Pollock 1982b; Pollock 1984). Henry (1983) also found ripe Acanthopagrus australis in Tuggerah Lakes in most months. For Monacanthus chinensis, very few individuals were caught in Lake Illawarra and Coila Lake, while no Gerres subfasciatus were caught in St Georges Basin and Coila Lake. As these populations are relatively self-sustaining within these estuaries, there may be some concem for the status of these stocks within these lakes, especially considering that both of these species are commercially harvested. 5.4.6 Recommendations This study highlights the importance of long-term study to understand pattems of natural recmitment variability in fish populations. The research undertaken in this study was the first to investigate pattems of recmitment of major commercial fish species in southem NSW, and to investigate the importance of ICOLLS as nursery habitats to the fish populations in the region. It is important that fiirther research on fish and fisheries south of Sydney occurs. For example, no studies on the biology of Acanthopagrus australis and Monacanthidae species on 233 the south coast have been undertaken. Apart from this study, there is little information on recmitment timing for many species, and further information on recmitment and spawning is needed. In particular for species that participate in migratory spawning mns it would be interesting to investigate the relative contribution of larvae from the northward spawning run compared to local spawning events to understand population replenishment in this region. It is also disconceming to note the lack of information available for Monacanthidae species, and the way in which they are freated by NSW Fisheries in their catch information. There is little understanding of regional and local current regimes for larval transport along the south coast region. Given the nature of the EAC in this region and the differences in recmitment strength among estuaries noted here, this information would be essential for fiirthering the understanding of recmitment dynamics in this region. And most importantly, the results of this study suggest that recmitment strength of fish communities in southem NSW between years is strongly linked to long-term rainfall cycles in the region and possibly El Nino episodes, and could be subject to a far greater degree of uncertainty than previously thought. If this is the case, it has important consequences for the management of the commercial and recreational fisheries sectors in this region, and the sustainability of fish populations. It is recommended that recmitment strength of the many species that are exploited by conmiercial and recreational fisheries in this region are investigated further. 234 Chapter Six Small-scale spatial variability in the shallow water fish communities of two intermittently open and closed lakes 6.1 Introduction Variability in the abundance, distribution and composition of species assemblages has been shown to occur at different spatial and temporal scales, and is an important component of habitats and ecosystems (Levin 1992). Previous research on the shallow water seagrass fish faunas of intermittently open and closed lakes and lagoons (ICOLLs) along the south-eastem coastline of New South Wales (NSW) revealed a complex picture (Chapters 3-5). There was high variability in pattems of species diversity and abundance, with little consistency to these pattems, both within and among estuaries. Fish assemblages within ICOLLs were characterised by a high number of species that were common to the entrance, central and upper locations, and thus there was a lack of distinct grouping of fish species on the basis of life history characteristics and/or salinity preferences. While these results were surprising, it indicated that local processes of individual ICOLLs may be a much more important factor in the stmcturing of these fish communities than more general concepts of geomorphology or biogeography. Previous chapters have discussed spatial and temporal variability at a regional scale, based on the experimental design of sampling three locations within six widely spaced ICOLLs, quarterly over three years. The results of this sampling program suggested that further sampling should investigate whether differences in the fish communities could be detected at a 235 smaller spatial scale and higher temporal scale. Spatial and temporal scale of samplmg have been shown to influence results m other fish sampling programs (Bell et al. 1992). These findings indicate that extrapolating pattems and processes detected at one scale to a different scale can provide misleading information. This is especially important when determining impacts from anthropogenic disturbances, and constmcting management and zoning plans for estuarine environments. Questions involving the management of estuaries often relate to the zoning of the estuarine environment for different activities, such as commercial and recreational fishing or the conservation of biodiversity. There has been some debate on the scale of management to be used for estuaries in NSW, particularly with the recent introduction of marine protected area legislation in NSW (NSW Fisheries 2001b). Seagrass beds within estuaries are one obvious scale of management as is a "whole of estuary approach" (Ferrell et al 1993). To date there have been no studies of the importance of small spatial effects in the stmcturing fish communities in estuaries on the NSW south coast. The objective of this chapter was to quantitatively investigate the effects of a much more smaller-scale spatial and higher temporal sampling of the fish communities of two ICOLLs; Lake Illawarra and Durras Lake. These two estuaries were chosen as they are very different systems in terms of shape and size, entrance conditions, and degree of catchment development and lake usage. This intensive smaller scale program would also allow for comparison of results from the previous larger scale program, and hence to investigate appropriate sampling and management regimes for fiiture monitoring 236 6.2 Methods 6.2.1 Study Sites A detailed description of Lake Illawarra and Durras Lake has been given in Chapter One (section 1.7). 6.2.2 Site Selection The aim of this study was to investigate distribution and abundance of fishes within ICOLLs over small spatial scales, namely metres to kilometres. Both lakes were divided into eight zones with four sites in each zone. Each lake was subdivided on the basis of sub-catchments. In Lake Illawarra, the major creeks entering the system are Macquarie Rivulet, Duck Creek, Mullet Creek and Brooks Creek, and thus, four zones could be delineated based on these sub catchments. The entrance region and eastem foreshore were separated into four zones (Figure 6.1). In Durras Lake, there are three major creek systems, Cumbralaway Creek, Benandarah Creek and Bridge Creek. There are also two smaller creeks systems, entering one bay in the eastem part of the lake. Subdivision of Durras Lake into eight zones was mainly on the basis of the shape of the lake, which has an irregular shoreline and several distinct arms and bays (Figure 6.2). Within each of the eight zones, fish sampling was conducted at four sites. The four sites within each zone were selected randomly, and these same sites were sampled for the entire program. The distance of the shoreline of each zone was measured in metres using GPS (Garmin Model GPS 12). A table of random numbers (Zar 1996) was used to determine the 237 position of the four sites. The seine net (see Section 3.3) was hauled once at each of the four sites. All sites were in shallow waters (<2m), and vegetation cover was primarily Zostera capricomi, with a percentage cover of at least 50%. Along the eastem foreshore from Purry Burry Point along the Windang Peninsula, the dominant seagrass species is Ruppia megacarpa, and hence sites 5 to 8 were located in Ruppia habitat. As well, there were few seagrass beds in Yallah Bay, and the three sites had to be placed in the one seagrass meadow (sites 25, 26 and 27). 6.2.3 Fish Samplmg Fish sampling was carried out according to the method described in Section 3.3. 6.2.4 Data Analysis Community stmcture was examined by multivariate techniques using the PRIMER 4.0 software (Plymouth Marine Laboratory). Hierarchical agglomerative classification analysis and multi-dimensional scaling (MDS) ordinations were employed to examine pattems in the stmcture of the fish community data for each lake. Analyses of the 32 sites within each lake used catch data that were pooled over the six sampling occasions. Two types of transformation were used on the data for separate analysis. A 4 root transformation (x ° ^) was used to emphasize the distribution of less common species in the analysis (Clarke 1993). A presence/absence transformation was used on the data to test for differences due to the composition and distribution of species in assemblages, thus eliminating the influence of abundance and giving equal weighting to rare species. Similarity matrices were calculated using the Bray-Curtis measure (Bray «fe Curtis 1957). The data were subjected to cluster 238 analyses using group average linking to constmct hierarchical agglomerative dendograms. In order to view spatial relationships, ordination employing non-metric multi-dimensional scaling was performed to generate two-dimensional ordination plots of the data. In all cases, the community relationships were displayed in three-dimensional plots because the associated stress levels were unacceptably high in two dimensions (Clarke 1993). 239 Figure 6.1: Lake Illawarra showing the 32 sampling sites within the eight zones (see Figure 1.1 for fiirther information on location). 240 Figure 6.2: Durras Lake showing the 32 locations within the eight zones (see Figure 1.1 for fiirther information on location). 241 6.3 Results 6.3.1 Entrance Conditions The entrance to Lake Illawarra was open during the entire sampling period between May 1999 and May 2000. Durras Lake was intermittently open and closed, with the entrance closed during the sampling events in May, August and October 1999. The entrance was artificially opened in the period between October and December 1999, and remained opened for the following sampling events in December 1999, Febmary and May 2000. 6.3.2 Salinity and Temperature The range of salinities in Lake Illawarra and Durras Lake was similar. In Lake Illawarra the lowest salinity value was 21.1ppt recorded at Site 14 and the highest was 39.7ppt was recorded at Site 131 (Figure 6.3A). Such high salinity values are not uncommon for certain areas of Lake Illawarrra, where the combination of extremely shallow water (<0.5m) and high air and water temperatures can lead to hyper-saline conditions (>36ppt). The range of salinity values in Durras Lake were from 21.1 ppt at Site DIO to 38.1 ppt at Site II (Figure 6.3B). In both lakes, there were no noticeable decreases in salinity values away from the entrance and salinity values were usually very even across all sites (Figure 6.3 A, 6.3B). The two estuaries also exhibited similar minimum and maximum temperatures, 11.5-30.5 °C for Lake Illawarra (Figure 6.4A) and a range of 10.8-26.1 °C m Durras Lake (Figure 6.4B), 242 (A) Lake Illawarra 4 0 3 5 3 0 a 2 5 2 0 1 5 13 1/3 1 0 5 0 1- CM CO u> (o h^ GO a> o .- CM«^U>tOI^«00>p»-OI«^ (B) Durras Lake 4 0 3 5 3 0 2 5 ;a 2 0 1 5 t/3 1 0 5 0 T- CM « in Figure 6.3: The range of salinity values (parts per thousand) recorded at each of the thirty-two sites within (A) Lake Illawarra; and (B) Durras Lake, from May 1999 to May 2000. Sites are labelled as in Figure 6.1 and 6.2. 243 (A) Lake Illawarra 35 -, •^ m in im u m o m axim u m ^ 30H 25 H o o o o ^ o f OOOOO^OOQO OO°°°°OO °° 0) 15 H ^ ^^^ ^ ^^ ^ ^ Z^ /Ci.^^ 1 0 - 5 - T—I—I—I—I—I—T -|—I—I—I—I—I—I—I—I—I—I—I—I—I—I—I i-cjco^mtor^coojOT-cJco^iotDNootnOT-cuco^iotoh-oocnoT-cvj r-i-T-T-i-.-i-.-i-T-C\lC\|CMC\ICMCMCVJCMCM (B) Durras Lake 35 -1 30 H o o O "^ 25 o o o o o o o o o 3 o o o OOO o ° % o o a 20 a £ 0) t- 15 10 - 5 - -i—I—I—I—I—I—I—I—I—r T—I—I—I—r -|—I—I—I—I—I—I—I—r S ite Number Figure 6.4: Maximum and minimum temperatures at sites within (A) Lake Illawarra; and (B) Durras Lake, based on data during each sampling event from May 1999 to May 2000. Sites are as labelled as in Figure 1 and Figure 2. 244 with minima and maxima values related to seasonal effects. Slightly higher temperatures were evident in Lake Illawarra, probably due to shallower water conditions. There was also some variability in temperature values at the enfrance region and along the eastem foreshore due to higher summer and winter temperatures recorded at these sites. 6.3.3 Fish Communities 6.3.3.1 Lake Illawarra A total of 25 963 fish were caught during this high intensity sampling program from Lake Illawarra. This catch was made up of forty-seven fish species, of which eighteen were considered of significance to commercial and recreational fisheries (Table 6.1). The most specious families were the Gobiidae (11 species) and Monacanthidae (7 species). In terms of individual numbers, the seagrass fish fauna was dominated by large catches of Gobiopterus semivestitus, Atherinosoma microstoma, Afurcagobius tamarensis and Ambassis jacksoniensis. These species represented approximately 80% of the total catch. The main economically important species among the catches were Acanthopagrus australis, Girella tricuspidata, Gerres subfasciatus and Rhabdosargus sarba (Table 6.1). Species diversity of the catches varied around the lake, with the lowest diversity at Site 16 (14 spp) to the highest diversity caught at site U (Figure 6.5A), both situated just to the north of Bevans Island in the entrance region (Figure 6.1). Twenty-eight species were caught at Site II but it is interesting to note that for ten ofthese species only one individual was captured. High species diversity was also found at Sites 114 and 115 (Zone 14) in the south-east comer of the lake, and at Site 119 (Zone 15) located in the north-east section. 245 73 o o 00 «i ON o —1 (N t~- ^ m ;^ o o o 00 00 t- a m o oll^o o ^ s o o zn o 00 00 a ^ (N rt o m NO rt ON m o o o rt (SI VO •^ "-p 4) m »—I <=> ^ ;Q O CN" fn T-H 1 ON a oo rt O m NO rt IT) o NO OO m o S) ite s o^J CZ3 OO f<) O rt •S2 •Si * s ^ a =0 •-us O 0, M bo Si S J» u a ^ •^ >» ^ K1,0 Co 02 tj -< 03 Co c^ H a. 246 00 oo t^ tN 0\ ao <7 94 ON oo fN (N NO o o t^ O r<^ (N •^ O SS^o 00 r^ SI ON oo 00 NO NO ^ :Q CN ro ?«g2-oS^o^^ NO o fO V-) ^ ro fN ro ON NO fN t^ fN rt rt NO ro o ON 00 >o ON 00 ro f^ 2; • CN f^ ON t^ WO 0\ ^ rt O CN NO rt^ •* o 2 -^ o CN '-^ O 'JJ- O O ro O a te s CN CN t3 OTJ r4 00 ca lA I—I NO 00 05 ro 2 O O rt ^ 3^o o wo « rt 00 ro oo — ro NO f- 2 rj- ^ lO NO 2 r^ rt O CN (N -^ CN rt ^ r: 00 CN ^ f^ ON 00 ?/7 5 .'>3 ••SS * § <4J * §42 I s ss * « grandici « n species bp « us laterali us exsquis ?natus § S 09 =n « tS I — 2 1>5 >H ^ bifi-i •^^ P bi i 1 ^ ••^4 "^ *^ "^ Crj ^ "a :a ilypnodo ilypnodo •biida e « vonigobi e vonigobi Sloya 5s 3 fas i*< ^ a, a^ e) 247 •a ro fN rt t-- rtOj^^ fN CN 00 NO o WO CN ON H ro WO CN CN 00 f? V ON O O NO NO o o T^ rt ON ON CN C/D 00 NO ro rt fN 2 O WO IQ-^ wo ro 00 CN C/2 O O CS CN r^ ON CN o o ON o -H o CN WO o o CN NO o ro C/3 1-^H •* 1 V ro T-H a CO ^ rt O NO 5^ rt o O NO o •* s; •* C/2 CN f^ 4) 1 WO ON ON O O NO o CN ON oa Kl CN o o JS 1.^ CN CN on «s So" wo a O O •* O O O O O oo wo CN CN O CN ^ O O CN CN JS a W a m^g^lai O 248 Low species diversity was consistently found in catches from Ruppia beds at Sites 16, 17 and 18, and also at Sites 117, 123 and 131, all located in the westem region of the lake. Afurcagobius tamarensis, Ambassis jacksoniensis, Atherinosoma microstoma and Philypnodon grandiceps were caught at all thirty-two sites. Combining all thirty-two sites, there were seven species with only one individual caught and six species with less than ten individuals caught over the study period. Out of these species, five belonged to the Monacanthidae family (leatherjackets). Other species that were rarely caught include Tylosurus gavialoides, a marine species, and two whiting species (Sillaginidae), which are found more commonly over sand habitat. However, species such as Enoplosus armatus and Petroscirtes lupus, which have been caught in these estuaries previously (Section 3.4, Table 3.2), were caught only once. MDS ordination plots were generated from the multivariate analysis using both a 4*^* root transformation and a presence/absence transformation. These revealed a high degree of similarity in the fish communities around the perimeter of Lake Illawarra (Figure 6.6). Cluster analyses using either transformation procedure resulted in the separation of the sites from Zone 12, which were situated in Ruppia seagrass beds along the eastem foreshore (Figure 6.7, Figure 6.8). These sites were relatively diverse (14 to 18 spp.), with species such as Girella tricuspidata, Gerres subfasciatus and Nelusetta ayraudi utilising this type of seagrass. However, at these sites, catches were very much dominated by large numbers of Atherinosoma microstoma. Site 14 was also an obvious outlier in the MDS plots, largely as a result of low catch numbers of all species. Apart from these, the remainder of the sites had a high degree of similarity in the composition of their fish faunas and clustered into one large group in the MDS plot (Figure 6.6). 249 (A) Lake Illawarra B 10- Slte Number (B) Durras Lake T-CNjco^m For the Lake Illawarra fish community data that was square root transformed, sites that were spatially close to each other tended to form clusters. For example. Sites 123 and 124 had approximately 84% similarity amongst their fish faunas (Figure 6.7). These two sites are situated both in Koonawarra Bay and had relatively low catch numbers, with the majority of the catch comprised of Afurcagobius tamarensis, Gobiopterus semivestitus, Philypnodon grandiceps and Atherinosoma microstoma. Sites 19 and 120, which are also situated next to each other had 82% similarity (Figure 6.7). Catches from these sites had very similar total numbers and had the highest numbers of Pelates sexlineatus. Presence/absence analysis revealed a different picture for the similarity of the composition of the fish faunas around Lake Illawarra (Figure 6.8). There remained a high degree of similarity among the sites, as shown by the MDS plot (Figure 6.6). Only two sites (Sites 16 and 17), those in the Ruppia seagrass, were separated from the rest of the sites. These had 90% similarity in their fish faunas (Figure 6.8). Notably, the rest of the sites were not grouped spatially (Figure 6.6, Figure 6.8). Suprisingly, it was quite common for the site groupings with the highest degree of similarity to be located opposite each other in a north/south orientation. For example, Sites 110 and 128 have 85% similarity between their fish faunas (Figure 6.8), but are situated at opposite ends of Lake Illawarra (Figure 6.1). 23 species were found at Site 110, and 21 species at Site 128, with 19 ofthese species common to both sites. Several of these species were not caught at many other sites, such as Achoerodus viridis and Tetractenos glaber. Sites 114 and 124 also had a high degree of similarity of catches, with twenty shared species, even though they are again located in different bays in opposite sections of the lake. Species that were not caught in high abundance in Lake Illawarra, such 251 (A) . 0.0 (B) Figure 6.6: Three-dimensional plots of the fish community data fi-om Lake Illawarra showing the thirty-two locations sampled (as labelled in Figure 1). Sampling events have been combined and data has undergone (A) 4* root transformation (stress =0.15) and (B) presence/absence transformation (stress =0.17). 252 Zone 1 (4) Zone 2 Zone 1 (1,2) Zones (29,3031) Zones (17) Zone 3 (10) Zone 7 (25,26,27) Zone 4(13) Zone 6 (21, 22) Zone 3 (9,11,12) Zone 5 (20,18) Zone 6 (23, 24) Zone 4 (14,15,16) Zone 5 (19) Zone 1 (3) Zone 7 (28) Zone 8 (32) 50 60 70 80 90 100 Bray-Curtis Similarity Percentage Figure 6.7: Dendogram showing results of MDS classification, using abundance data for fish species caught in Lake Illawarra, between May 1999 and May 2000. Zones are shown with site numbers in brackets. Data has undergone a 4* root transformation, and sampling events have been pooled. 253 Zone 2 (6,7,8) Zone 1 (4) Zone 8 (31) Zone 5 (17) Zone 6 (21,22) Zone 7 (26) Zone 3 (11) Zone 5 (18) Zone 4(13) Zone 3 (9) Zone 5 (20) Zone 6 (24) Zone 7 (25,27,29) Zone 8 (29) Zone 4 (18) Zone 2 (5) Zone 3 (12) Zone 4 (15,16) Zone 1 (1,2,3) Zone 8 (30) Zone 3 (10) Zone 8 (28,32) Zone 5 (19) 60 70 80 90 100 Bray-Curtis Similarity Percentage Figure 6.8: Dendogram showing results of MDS classification, using abundance data for fish species caught in Lake Illawarra, between May 1999 and May 2000. Zones are shown with site numbers in brackets. Data has undergone a presence/absence transformation, and sampling events have been pooled. 254 as Meuschenia freycineti, Meuschenia trachylepis and Monodactylus argenteus, were caught at both of these sites. Sites from the entrance region (Zone II) were also more similar to either zones in the south-eastem section of the lake or to the north-east section, but not to those zones situated dfrectly across the lake (Figure 6.7, Figure 6.8). It would therefore appear that settlement processes of fish species into this ICOLL occurs along on a north-south orientation, resulting in a similar assemblage of fish communities in the south-east and north east sections of the lake. This observation is discussed fiirther in Section 6.4. 6.3.3.2 Durras Lake The catch from Durras Lake yielded 31 923 fish representing forty-eight fish species (Table 6.2). Twenty of these species are considered to be of importance to commercial and recreational fisheries. In relation to abundance, the catch was dominated by small, cryptic species with nearly 85% of the total numbers comprised of Gobiopterus semivestitus, Philypnodon grandiceps, Afurcagobius tamarensis and Ambassis jacksoniensis. In terms of species diversity, the Gobiidae and Monacanthidae families were the most specious with twelve and eight species found respectively. The commercial species with the highest catches in Durras Lake were Gerres subfasciatus, Girella tricuspidata, Acanthopagrus australis, Mugil cephalus and Rhabdosargus sarba (Table 6.2). The numbers of species caught varied around Durras Lake, from thirteen species at Sites D9 and D29, to 23 species at Site D16 (Figure 6.5B). Numbers of species were relatively even with the majority of sites ranging from 16 to 20 species. In terms of abundance, there was often large differences among sites, but this was commonly attributed to schools of Gobiopterus semivestitus, Ambassis jacksoniensis, or large number of Philypnodon 255 grandiceps being caught (Table 6.2). Site D9 had consistently low numbers of individuals caught over the year, and this could be related to its location at the edge of a channel (see Figure 6.2). There were only three species that were caught at all thirty-two sites: Gobiopterus semivestitus, Philypnodon grandiceps and Afurcagobius tamarensis. There were five other species that were missing from only one or two sites: Redigobius macrostoma, Ambassis jacksoniensis and Amoya bifrenatus, plus two commercial species, Acanthopagrus australis and Gerres subfasciatus. There were a number of species that could be considered uncommon or rare. For example, seven species were caught only once and as a single individual. Some species such as Platycephalus fuscus and Cnidoglanis macrocephala are usually found over sand or mud habitat and thus low catches of these species are not surprising. However, species such as Omobranchus anolius (oyster blenny), were in low numbers, indicating this species is relatively uncommon or that the sampling method is not suited to catching this species. There were also nine species that had less than ten individuals caught over the sampling period, of which three species belonged to the Monacanthidae family (leatherjacket) and two to the Syngnathidae family (pipefish). MDS plots indicate that there was a high degree of similarity among the fish communities in the seagrass beds around the perimeter of Durras Lake (Figure 6.9). The dendograms from the cluster analyses also revealed a high level of similarity, but there was also some degree of association of the fish communities with certain regions within the lake (Figure 6.10, Figure 6.11). Using the 4 root transformed data the fish faunas at the entrance region (Zone 1) and at the channel area (Zone 3) were most similar to each other (Figure 6.10). On the dendogram, there was also a general mixing of the sites from the bays and upper regions of 257 •* CN NO NO O ro ^^ o o o -^ CN •* O OO o •* CN 1—.C ,-H 00 H NO t—I ^H ro ro CN 00 CO O ON fN) O rt WO rt o a CN -t CN CN w^ tS ite s t/3 >^ ^..^ OO t- CN 1 ii WO CN ro NO a ON ^ 0\ NO rs t3 ite s C/2 ^^ ^^ Tf NO CN 1 4> CN t-- CN a CN O ^ o o ^ ro •^ N ite s 00 '—' ^ IT) CoN a> t^ a f—( 00 00 rs t3 B ro (N rt t>o V ro 00 ro CN 2 ^ o j:; o ro ro ro on 4) ON O ^ ro 00 o wo CN O ^ O O 00 ro bo CN oo 00 3 " CJN CN o o 22 « rt t^ 00 CN r^ ro NO CN CN ON ro !/3 >1 •S3 I is. 4!- K •I S O I J V § S 5 « "3 •S •"«a boS 09 K a s * « I t 08 -S ^ 5r § -£3 -a S o s » 3 r bo •I It es .a a '< u k. a C 1^ a 8 •o p O c 1 ^ 5^ p w) a G y s '^ u & :§ !< 1 §.^ S "2 5 a S S p §) to 5 au >* s? o I a ^ O S p ^ ^ Ci,0 Co V J S H a. 5 X PLH 258 Tj- r- ON ON O ON ro rt( •^ ON ^ CN ro rti NO NO ^ ro rt 00 NO rt CN ::o a ^ o o O ro !/3 • ON wo Tf NO WO — CN o o o wo c^ NO O ^ o ^ -N o C/3 S<^ rt - NO o 2o rt o o wo CN ^ ON ro oo NO ro ro rt 00 o t^ wo wo Tt VI NO CN NO rt ro CO m ro wo o o CN to * * es a bo E? i I on 4> K ^.1 4> S I § J5 -b es i! O O es s a u •s a « o es T3 M :a -w •1 .c o •5 "« is 4> 'S '2 C r " K S a^ (5 a w0 ^ a. 259 ro •a r.- 00 ON CN 2§roSSS ON rt r^ON^^^ CN ON O ^ 'Zl '^ ro H CN 00 <7 NO NO V ON ON rt I NO O O ro ^ r- wo O O O rt o o WO NO ON O o CN 00 0) wo ON NO wo o —> NO O O O CN O O NO ON CN CO CN ^^£5; CN WO C/3 NO W rt wo ON wo Tf O O wo CN NO rt o ON 2 ro a cs C3N o wo ro S3 ^ ^r^ i/3 O •n CN wo o wo o w^ o t-g:J- O 'Jl- o O O ND 2 <^ "* ON wo r- o CN wo &0 NO 4> ro 00 oo CN O O wo CN rt rt o CN wo CN O o o ^ 00 o o P « CN O r—I ii C3N ON a ;::;iooo^o^| CN o rt ;^ rt rt o O CN on CN 00 00 WO o o o >"" '-' O rt O O CN NO O O 0\ ^ ro ro wo CN « rt ro wo (-, rt « s * * •2 5 i"l * -a I a) .5r a a •IS •1 -S •SX u •^ e« oloru «> emive osus K S enia tida i 5 s taay ichth atus a « .bo •*.* « bo S' -K -s; a ^5 r* u o >«u; Sa "•»-^* a'— . a (»^ a a § T3 o S 5 the lake. There was no distinct clustering pattem of these zones, but there was an overall a high degree of similarity in their species composition (Figure 6.9, Figure 6.10). In many cases, adjacent sites were highly similar (i.e., between 85-90% similarity). There were also instances where sites from different areas of the lake had a high degree of similarity in their fish fauna. In these cases, there was a large number of shared species. For example. Sites D6 and D19 have 87% similarity in their fish communities from the presence/absence dendogram (Figure 6.11). These sites are both bay sites but are in distinct separate arms of Durras Lake (see Figure 6.2). Twenty species were caught at Site D6 and nineteen from Site D19, but seventeen ofthese species were common to both sites. Those species not shared were represented by only one individual. The MDS plots revealed that sites that were situated in the arms and bays of Durras Lake were most comparable in terms of species diversity and abundance of individuals. Sites from different bays were often more similar to each other than to sites within their own bays. However all these sites were situated in close proximity on the dendogram (Figure 6.10). The sites from the upper regions of the ICOLL (Zones D6, D7 and D8) also tended to cluster together. Sites D29 and D31 separate out with a presence/absence transformation due to only 13 and 14 species respectively caught at these sites over the year. Zones D7 and D8 were characterised by low numbers of a few leatherjacket species (Table 6.2). The entrance region (sites Dl-4) was characterised by a low catches (Table 6.2), and hence were situated closely together on the dendogram using the 4* root transformation (Figure 6.10). In terms of species diversity, Sites Dl and D2 had relatively high species diversity and 261 (B) -0.5 . 0.0 Figure 6.9: Three-dimensional plot from the multidimensional scaling (MDS) analysis of the fish community from Durras Lake. Sites are labelled as in Figure 2. Sampling events have been combined and data has undergone (A) 4"' root transfr)rmation (stress = 0.14), and (B) presence/absence transformation (stress = 0.15). 262 Zone 3 (9) Zone 1 Zone 3 (10,12) Zone 7 (28) Zone 8 (29,31) Zone 4 (13,15) Zone 7 (26) Zone 8 (30) Zone 6 (21) Zone 3 (11) Zone 2 (8,6) Zone 4 (16) Zone 5 (19) Zone 6 (233) Zone 7 (25) Zone 2 (5,7) Zone 5 (17,18,20) Zone 7 (27) Zone 4 (14) Zone 6 (22) Zone 8 (32) 50 60 70 80 90 100 Bray-Cxirtis Similarity Percentage Figure 6.10: Dendogram showing results of MDS classification, using abundance data for fish species caught in Durras Lake, between May 1999 and May 2000. Zones and site numbers are shown in brackets. Data has imdergone a 4* root transformation and sampling events have been pooled. 263 Zone 8 (29,31) Zone 1 (1,2) Zone 4(13) Zone 1 (3) Zone 3 (9,10) Zone 4 (14) Zone 3 (12) Zone 4 (17) Zone 2 (5,7) Zone 6 (21,23) Zone 2 (6) Zone 3 (11) Zone 4 (16) Zone 5 (19,20) Zone 1 (4) Zone 2 (8) Zone 5 (18) Zone 6 (24) Zone 7 Zone 8 (30) Zone 4 (15) Zone 6 (22) Zone 8 (32) 60 70 80 90 100 Bray-Cvirtis Similarity Percentage Figure 6.11: Dendogram showing results of MDS classification, using abundance data for fish species caught in Durras Lake, between May 1999 and May 2000. Zones are shown with site numbers in brackets. Data has undergone a presence/absence transformation, and sampling events have been pooled. 264 shared 16 species between them. Site D3 had one of the lowest numbers of species (14 spp) out of all the sites and was most similar to two of the channel sites. Twenty species were caught at Site D4 and in terms of common species it was more comparable to sites from the bays. 6.3.4 Spatial and temporal patterns of commercial fish species The majority of the commercially important fish species caught in Lake Illawarra and Durras Lake would be considered ocean spawning. The main exception is Gerres subfasciatus, which is considered an estuarine spawning species, and was captured from both estuaries in large numbers. Notably the estuarine spawning leatherjacket species, Monacanthus chinensis, was not caught in Lake Illawarra, even though it has been found in this estuary previously (see Chapter 3), and only 2 individuals were caught in Durras Lake in Zones Dl and D3 (Table 6.2). The number of ocean spawning species varied quite erratically within Lake Illawarra. The highest number of ocean spawning species were caught at Site II at the entrance zone, and also at Sites 111, 113, 114, 115 and 119 which are located in the south-east and north-east sections of the lake (Figure 6.12A). Similarly in Durras Lake, the number of ocean spawning species caught varied among sites. The highest numbers of ocean spawning species were caught at sites D13, D16, D18, which are bay sites, and at site D21, which is in the central area of the lake (Figure 6.12B). There was a decline in the number of ocean spawning species at the upper reaches of the lake, but these numbers were comparable to those found at the entrance region (Figure 6.12B). 265 (A) Lake Illawarra 10 -1 /\ / 8 - A (A 6 - Ta 1 i \l \ /^ E 4 - 8 1/ I 2 - 1—1—I—I—n—r—i—I—I I I—n—m—n—n—i i i i—n—i i i—i i i—n T-CNico->i-m (B) Durras Lake 10 -1 /\ / 8 - A I CO 6 - \l \ A I 4 - "S V 6 1—r T-r I I I I I I ••-CNim-*ir>(Dt^ooo)Oi-CNim'*io(Ot^ooo>OT-CNic«)->a-in(Ot~coo>Oi-CN) i--.-T-i-T-T-T-i-T-.,-CNICNJCNlCNICNICNlCNICNICNlCNJCOCOC0 Site Number Figure 6.12: Total nimiber of commercial fish species caught at each site in (A) Lake Illawarra and, (B) Durras Lake, from May 1999 to May 2000. Sampling events have been pooled. Sites are as labelled as in Figure 1 and Figure 2. 266 Catches of recent recruits to the seagrass beds (those less than 40mm FL) and juveniles (>40 mm and < 100mm FL) of the dominant commercial fish species are shown in Table 6.3 for Lake Illawarra, and in Table 6.4 for Durras Lake. The majority of the catch was less than 40nim, indicating they had recently settled (Worthington et al. 1992). The main exception was Meuschenia trachylepis, which was caught as large juveniles or sub-adults in both estuaries. Recruitment of Mugil cephalus was also quite weak in both estuaries, particularly Lake Illawarra (Table 6.3). Recruitment of sea mullet occurred during December in Durras Lake, after the entrance was opened, with high catches of small juveniles caught in Zones D2 and D5, while Zone Dl had high numbers of larger juveniles (Table 6.4). 6.3.4.1 Acanthopagrus australis For Lake Illawarra, high numbers of Acanthopagrus australis were caught across a range of months, with the highest catches in increasing order during May, August and December 1999 (Table 6.3). New recruits were found during all of these sampling events. While larger individuals (>50mm FL) were caught during May, a high proportion of individuals were less than 20mm (Figure 6.13). During August 1999, all of the Acanthopagrus australis caught were less than 20mm. The December catch consisted of slightly larger individuals, indicating that recruitment had occurred slightly before December. Nevertheless, the majority of the catch was approximately 20mm FL (Figure 6.13). The distribution of the new recruits changed with each sampling event. For example, in May 1999, the highest abundance of Acanthopagrus australis was caught in the south-westem section of the lake in Zones 17 and 18. In August the highest abundance was in Zones II and 13, and in December the catch was 267 Table 6.3: Total abundance of small juveniles and large juveniles of dominant commercial species caught in Lake Illawarra by zones, with site numbers given for each zone. Small juveniles are defined as those less than or equal to 40mm FL. Large juveniles are defined as greater than 40mm FL. Ocean spawners are denoted as (O). Lagoon spawners are denoted as (L). Month Small Juveniles (04Onim) Large Juveniles (>40mm) Zone Zl Z2 Z3 Z4 Z5 Z6 Z7 Z8 Zl Z2 Z3 Z4 Z5 Z6 Z7 Z8 Site Nos 1-4 5-8 9- 13- 17- 21- 25- 29- 1-4 5-8 9- 13- 17- 21- 25- 29- 12 16 20 24 28 32 12 16 20 24 28 32 Mupl cephalus (O) May 1999 1 9 August 1 6 1 2 October 1 December 1 2 7 2 2 February 1 1 3 1 12 May 2000 r 3 1 1 1 Total 5 0 0 0 7 1 13 2 13 0 3 14 1 0 2 0 Meuschenia trachylepis (0) May 1999 2 14 54 1 5 7 August 1 October 1 4 December 3 2 February 9 7 5 14 5 May 2000 1 2 4 2 Total 0 0 0 0 1 0 0 0 11 0 21 59 4 30 17 0 Girella tricuspidata (O) May 1999 13 8 2 8 1 2 3 1 August 1 1 3 1 1 3 October 33 9 19 13 37 39 7 4 1 5 6 8 2 2 1 December 3 1 5 6 34 11 10 2 3 2 February 6 5 2 1 1 2 2 8 14 1 May 2000 5 1 5 1 1 3 4 4 1 Total 61 12 35 26 77 61 18 10 6 1 12 18 26 6 5 5 Acanthopagrus australis (O) May 1999 6 1 1 8 1 25 21 4 1 34 1 2 5 August 70 2 66 18 4 6 2 October 2 1 2 1 1 2 1 2 December 15 42 19 72 25 6 7 2 2 5 5 1 February 3 2 7 1 2 May 2000 6 8 4 fi Total 93 9 109 31 101 31 37 30 6 2 7 42 10 5 6 11 Gerres subfasciatus (L) May 1999 3 31 2 5 1 47 22 5 2 August 1 5 13 8 October 1 1 3 1 1 1 2 5 3 13 2 December 2 February 7 1 10 1 2 3 May 2000 2 1 4 2 3 Total 4 32 7 14 15 4 55 34 3 1 8 11 5 13 2 8 Rhabdosargus sarba (0) May 1999 August 4 1 October 3 10 1 49 1 December 3 18 1 48 7 February 7 May 2000 11 1 1 4 18 5 1 1 Total 21 12 19 115 5 8 0 1 7 0 0 0 0 0 268 Table 6.4: Total abundance of small juveniles and large juveniles of dominant commercial species caught in Durras Lake by zones, with site numbers given for each zone. Small juveniles are defined as those less than or equal to 40nim FL. Large juveniles are defined as greater than 40mm FL. Ocean spawners are denoted as (O). Lagoon spawners are denoted as (L). Month Small Juveniles (<40nim) Large Juveniles (>40mm) Zone Zl Z2 Z3 Z4 Z5 Z6 Z7 Z8 Zl Z2 Z3 Z4 Z5 Z6 Z7 Z8 Site Nos 1-4 5-8 9- 13- 17- 21- 25- 29- 1-4 5-8 9- 13- 17- 21- 25- 29- 12 16 20 24 28 32 12 16 20 24 28 32 Mugil cephalus (0) May 1999 August October December 25 29 1 40 1 February 1 12 2 9 1 May 2000 1 2 1 Total 1 37 0 1 29 2 0 0 42 11 0 2 0 1 0 0 Meuschenia trachylepis (O) May 1999 1 2 1 4 5 1 August 1 October 3 1 2 1 December 1 2 February 5 2 May 2000 1 1 2 10 Total 0 0 0 0 0 1 0 0 1 6 1 8 10 17 1 1 Girella tricuspidata (0) May 1999 7 4 3 1 5 4 3 August 1 2 1 October 3 2 1 2 1 1 December 2 18 8 24 6 38 22 1 23 5 February 13 61 26 19 24 9 2 2 3 9 1 2 May 2000 8 4 1 3 3 1 2 1 9 Total 2 46 77 31 43 33 48 3 31 8 5 10 35 15 3 1 Acanthopagrus australis (O) May 1999 1 1 1 August 1 October 2 December 5 4 5 21 72 81 19 2 1 4 3 1 2 February 5 1 2 1 21 3 13 1 4 3 2 3 7 May 2000 3 1 9 1 1 6 1 2 Total 6 9 7 6 42 84 94 20 8 5 4 7 10 1 9 4 Gerres subfasciatus (L) May 1999 9 2 1 6 10 1 1 August 9 35 4 1 9 1 1 2 October 2 65 1 4 9 14 3 1 9 2 5 8 2 December 1 1 9 2 1 2 2 5 February 1 2 1 1 9 8 4 3 4 2 May 2000 5 84 87 107 3 13 1 1 Total 20 109 6 97 106 107 29 6 32 19 7 3 13 3 12 7 Rhabdosargus sarba (0) May 1999 August October December 1 3 6 2 48 36 17 February 1 May 2000 2 1 Total 1 4 2 6 2 49 36 17 0 0 0 0 0 0 0 0 269 (A) (B) May 1999 M^1999 I 30. 13 14 19 20 25 28 30 31 'OH—I—I—I—I—I—I—I—I—I—I—I—I—r— 1 2 3 6 9 13 14 19 20 25 28 X 31 Site August 1999 August 1999 5 |t4. 'i —T I I I I I I I 1 1 I I I I 2 3 4 6 7 11 12 19 20 21 22 28 31 32 SHe DecaiiCTl999 Decemberl999 60- C 40 1 30- ^40 u. 20- |30H E 10- •I 20 *.-•• * "I I I I I I"-T I I I I I I—T I I I I T—\ I I 1 10. I I I I I I I I I I I ] I I I I I I I I I I I 12 3 5 9 1011121314 151718192122232427283032 12 3 5 9 10111213 14151718192122232427283032 Site Site Figure 6.13: (A) Total numbers of Acanthopagrus australis caught in Lake Illawarra during May, August and December 1999; and (B) corresponding mean fork length (mm) of individuals. Lines denote standard error. Site numbers are shown. 270 (A) •)0 -1 iO - c n 1 30 - I 20 - 10 - ^ -XV 0 - —I—I—r—-|—I—I—I—I 1 I—I—1—I—I—I—I—I—I—I—1—r- 2 4 6 7 9 10 15 16 17 18 20 21 22 23 24 25 26 27 28 29 32 (B) 70 -, 60 - E 50 - E, B) 40 - 5 O 30 U. c S 20- • • • 9 10- -|—I—I—I—I—I—I—I—I—I—I—I—I—I—I—1—I—I—I—I—r- 2 4 6 7 9 10 15 16 17 18 20 21 22 23 24 25 26 27 28 29 32 Site Figure 6.14: (A) Total numbers of Acanthopagrus australis caught in Durras Lake during December 1999; and (B) mean fork length (mm) of individuals caught during this period. Lines denote standard error. Site numbers are shown. 271 concentrated in Zones 13 and 15 in the north-east section of the lake. The effect of entrance closure from May 1999 to October was quite evident in Durras Lake, with a distinct lack of ocean-spawning species, less than 40mm caught in this period (Table 6.4).. The entrance was artificially opened between the October and December sampling events and the highest number of Acanthopagrus australis were caught shortly after (December 1999) (Table 6.4). For the December sample the mean length of the majority of the catch ranged from 13.5 to 22.5 mm FL, with a few larger juveniles caught as well (Figure 6,14). The greatest number of individuals was concentrated in the middle to upper sections of Durras Lake, namely Zones D6 and D7 (Table 6.4). 6.3.4.2 Girella tricuspidata The highest catches of Girella tricuspidata in Lake Illawarra were during the months of October and December 1999 (Table 6.3). During October 1999, Girella tricuspidata were found at 27 of the 32 sites and the majority of the catch ranged from approximately 20 to 40mm FL (Figure 6.15). Sites of highest concentration of individuals were Zones II, 15 & 16 (Table 6.3). During December, Girella tricuspidata were found at fewer sites and the catch was of small sized fish, less than 30mm FL (Figure 6.15). There was also a less even distribution of individuals, with the highest concentration of small juveniles in Zone 15 (Table 6.3) Recruitment was highest for Durras Lake during December 1999 and February 2000 (Table 6.4). 272 (A) (B) 30- 60-, October 1999 October 1999 E 50-^ B, 8 20' J) 40' € £ S 30- 20- •t.f i " I I I I I I I J I I I I I I I I I I I I I I I I I I 10- 11 11 I I I 11 11 I I I 11 I I I I I I I I I I 12 3 4 5 8 9 101112131517181920212223242526273032 12 3 4 5 8 9 101112131517181920212223242526273032 SHe Site December 1999 December 1999 ^60. B)50 c 0) -1—I—I—I—1—I—I—I—1—I—1—I—I—1—I—I—I— -T 1 1 1 1 1 1 1 1 1 1 1 1 1 1— 1 2 5 10 11 13 15 17 18 19 20 21 22 27 28 30 32 5 10 11 13 15 17 18 19 20 21 22 27 28 30 32 Site Site Figure 6.15: (A) Total abundance of Girella tricuspidata caught at sites within Lake Illawarra during October and December 1999; and (B) corresponding mean fork length (mm) of individuals during those periods. Lines denote standard error. 273 In December 1999, many of the Girella tricuspidata caught were less than 20mm FL, with individuals as small as 12mm FL (Figure 6.16). Like Lake Illawarra, there was no pattem to where the new recruits were caught, with the highest catch distributed aroimd the lake at sites D2, D19 and D27. During February 2000, the catch was of a larger size, ranging in length from 17 to 65mm FL, with the majority of the catch between 20 and 40mm FL (Figure 6.16). The pattem of distribution was different to the previous sampling event and the highest abundance of Girella tricuspidata were concentrated at the entrance to various bay sections at sites Dl 1 and D12, and also within bay arms at sites D16 and D17. 6.3.4.3 Gerres subfasciatus The estuarine-spawning Gerres subfasciatus was the dominant commercial species caught in Durras Lake when the entrance was closed from May to October. Recruitment was evident in the August and October samples, confirming this species spawns within ICOLLs. The greatest number of small juveniles were caught in Zone D2 (Table 6.4). A substantial recruitment event also occurred in May 2000, with large numbers of Gerres subfasciatus caught in Zones D4, D5 and D6 (Table 6.4). Recruitment of Gerres subfasciatus was weaker in Lake Illawarra, with only relatively high numbers of small juveniles only caught in May 1999 in Zones 12,17 and 18 (Table 6.3). 6.3.4.4 Rhabdosargus sarba Within Lake Illawarra, recruitment of small individuals was highest during December 1999 (Table 6.3), and the majority of the catch was less than 25mm FL (Figure 6.17). New recruits were also caught during October 1999 and May 2000, when the fork length ranged from 274 (A) (B) December 1999 December 1999 S. 70 9 t I 60 I- § 10 E 30 20' i/ \A/-^\^ *•-•- 10 -T 1 1 1 1 1 1 1 1 1 1 1 1 ( 1 1— 5 6 7 10 11 12 16 17 18 19 20 21 22 23 24 27 6 S7 10 11 12 16 17 18 19 20 21 22 23 24 27 Site Site 35 Februaiy 2000 February 2000 30- 8 25- C B) SO' c 20- I 40 To 15- iM /"•"\ < II \\ ** —1—I—I—I—I—I—I—I—I—r—I—I—I—I—r—I—I— —I—I—I—I—I—I—I—I—I—I—I—I—I—I—1 6 6 9 10 11 12 16 17 18 20 21 23 24 25 27 28 3D 10 11 12 16 17 18 20 21 23 24 25 27 28 30 Site Site Figure 6.16: (A) Total abundance of Girella tricuspidata caught at sites within Durras Lake during December 1999 and February 2000; and (B) corresponding mean fork length (mm) of individuals during those periods. Lines denote standard error. 275 40- SO-i Octoba-1999 Deceniier 1999 ? 45- Ii E 35 B, E £ 40- g> 30- ng t 5 35- •£ o £ 25 u. 30- c II c IB 25- ^ 20' 1 20- • * • 1 • 1 * • • 15- —1— —I— —1— 1 1 1 Jill —[— 1 t 1 1 18 19 27 28 15 19 20 1 3 9 10 11 12 14 SHe Ste 30' May2000 ¥ 25 E, c 20- •K .2 •\ -I 1 1 1 1 1 1 1 1 1 1 r— 3 4 8 10 15 16 19 20 21 24 26 28 Site Figure 6.17: Mean fork length (mm) of Rhabdosargus sarba caught at sites within Lake Illawarra during October 1999, December 1999 and May 2000. Lines denote standard error. 276 approximately 25 to 35mm in October (Figure 6.17). Small juveniles were caught in Zones II to 17 throughout the sampling period, but the highest concentrations of individuals were found in Zone 15, particularly in October and December (Table 6.3). In Durras Lake the recruitment of Rhabdosargus sarba was evident only during December, either none or very few individuals caught during the other sampling events. This was probably due to entrance closures during these periods (Table 6.4). There were no trends evident in size and distance from the entrance, with the fork length ranging from 15 to 20mm 30 n December 1999 I 25^ I £ c t» 15- 10. T I I i I I I i I I 1 I 1 1 1 4 8 15 17 18 22 23 24 25 26 27 28 29 32 Site Figure 6.18: Mean fork length (mm) of Rhabdosargus sarba caught at sites within Durras Lake during December 1999. Lines denote standard error 277 FL at all sites throughout the lake where Rhabdosargus sarba were caught (Figure 6.18). The highest number of Rhabdosargus sarba occurred at Site D23 (Zone D6), which is approximately situated in the middle section of the lake. Other sites where high catches of new recruits were made were similarly located in the middle and upper sections of the lake, while very few small juveniles were caught in the entrance region or zones closest to the entrance (Figure 6.18). 6.4 Discussion 6.4.1 Structuring of Fish Communities within estuaries The shallow water fish faunas of both Lake Illawarra and Durras Lake were characterised by a high degree of similarity between sites. However, while these ICOLLs were similar in this respect there were also differences in the structuring of fish communities within each of the lakes. For Lake Illawarra, cluster analyses demonsfrated that both the relative abundance and composition of species associated with shallow water seagrass from sites separated by small spatial scales did not differ consistently. Overall there was a distinct lack of grouping of sites within Lake Illawarra and a general mixing of fish communities throughout the lake. In terms of abundance, similarity was high between sites located next to each other, indicating that samples were relatively homogenous. There seemed to be little variation at the scale examined here (metres to kilomefre). With the removal of the effect of abundance, disjunct sites showed similarity, as they had a large number of shared species. The high similarity among sites appeared to be due to the presence of a selection of species at many sites. 278 suggesting that there was little structuring influence at small spatial scales on the fish community. The fish fauna of Durras Lake also exhibited a high degree of similarity throughout the lake, but there were again differences in structuring of the fish community from the entrance locations to the upper regions of the lake. The fish fauna from sites located in the entrance region and those along charmel areas were more similar to each other than to the fish fauna inhabiting the bays and upper regions. Sites from these distinct bays and the upper reaches of the estuary also showed a high degree of similarity to each other. However, unlike other estuarine systems, where differences in fish community structure along the estuarine gradient have been attributed to environmental factors, particularly salinity (Blaber & Blaber 1980; Humphries et al 1992; Sheaves 1996; West & King 1996), the structuring of the fish community within Durras Lake did not appear to be related to the influence of salinity. The range of salinity and temperature values at sites in Durras Lake was very similar, with no evidence of a progressive decrease in salinity away from the estuary mouth. For both Durras Lake and Lake Illawarra, salinity was more variable between sampling events than between sampling sites. When fluctuations in salinity within the lake did occur between sampling events, these changes were consistent throughout the entire estuary. There was also no apparent relationship between the mean salinity values of the lake during sampling events and the total number of species caught. Even though high species diversity was found during high salinity events (>30ppt) the same number of species was caught during medium salinity events (21-27ppt). It would appear that the change in salinity of approximately 10-14 ppt, as recorded in this study, does not greatly influence the stmcture of these fish communities, or the penetration and survival of marine affiliated species in these estuaries. 279 As most ICOLLs on the NSW south coast are artificially opened, it is difficult to determine the possible effects of long periods of closure, on the composition of the estuarine fish fauna. In the Bot River Estuary in South Afiica, mass mortality of nine marine fish species occurred when salinity declined to 3 parts per thousand after a long period of entrance closure (Bennett 1985). However, it is less likely that such low salinity levels would be reached in many of the ICOLLs in SE Australia, as rainfall is generally low. It has been suggested that some fish species can tolerate large fluctuations in salinity (Young et al 1997). For example, mullet species in the Moore River Estuary in Westem Australia, penetrated the middle and upper estuary where salinities were consistently 4.5ppt (Young et al. 1997), and the sparid Rhabdosargus holubi can tolerate salinity fluctuations from 0.7 to 70ppt (Blaber 1973). Hence, the stable salinity values recorded within Durras Lake and Lake Illawarra, and the small range of salinity values recorded over time would probably have little effect on the survival of many of these stenohaline species. This would also allow their penetration of these fish species into all areas of the estuary, contributing to the similarity of the fish communities from different areas within these estuaries. 6.4.2 Influence of physical factors on small-scale spatial and temporal patterns Physical factors, rather than environmental influences, may play a more important role in the structuring of the shallow-water seagrass fish communities in these systems. Examples of important physical factors that may effect fish communities are the shape and size of the ICOLL and hydrological influences, such as the effects of wind-induced water transport. Dmras Lake has an irregular shoreline with several distinct bays, and a large saltmarsh area in the cenfral region of the lake. The shape of Durras Lake could act as a physical barrier to tidal 280 movement and transport of mdividuals. Sogard et al (1987) proposed that the network of shallow banks in Florida Bay (USA) caused a restricted water circulation, and thus limited transport of larvae. In a similar manner, differences in the fish composition of the enfrance and channel areas to bay sites of Durras Lake could easily occur due to physical barriers to the transport of individuals. In contrast. Lake Illawarra has an entrance channel leading into a wide semi-circular basin, lacking distinct arms and bays, and enhancing the flow of water movement throughout the whole lake. Wind-driven transport mechanisms are likely to be an important factor influencing fish commimity pattems in Lake Illawarra. Lake Illawarra is a shallow water system, with an average water depth less than 2m. Water circulation within shallow estuaries have been found to be very sensitive to the wind direction (Jager 2001). In a study of estuaries in Cape Cod, USA, it was found that there was a sfrong influence of winds on the flushing and circulation pattems due in part to shallow depth, which accentuated the influence of wind stress (Geyer 1997). With the absence of significant tidal movement in Lake Illawarra, wind direction and velocity may be the most important factor influencing circulation pattems and therefore larval supply and transport. For other shallow estuaries, such as the Galician estuary in Spain, strong wind speeds greatly influence the sea surface current, and the current speed induced by wind is greater than the one induced by tide (deCastro et al 2000). The influence of wind speed and direction has previously been suggested as a cue for recmitment to commence, or as an mfluence on the advection of larvae in nearshore waters (e.g.. Smith 1999). Correlations between interaimual variation in marine fish recraitment and wind-induced transport have been found for some fish stocks along the eastem seaboard of 281 America (Yoder 1983), and for brown sole m the Sea of Japan (Nakata et al 2000). Wind- driven circulation is also thought primarily responsible for the transport of cod larvae in the Baltic Sea (Voss et al 1999). However, it has rarely been applied to the distributional pattems of juveniles within small-scale environments such as estuaries. It is generally accepted that a combination of larval behaviour, initial spawning location and timing, and hydrological and meteorological forcing, is critical to the retention of, and/or transport of yoimg fish. Lake Illawarra is subject to sfrong winds for the majority of the year (Figure 6.19), and numerical modelling has predicted strong flow pattems below the Im depth contour for different wind conditions (Figure 6.20). In this study, there appeared to be a strong SW/NE relationship in the similarity of the fish communities (see Figure 6.8), indicating settlement pattems and mixing of the fish species along this gradient. Also the sites at the entrance zone were most similar to those in the NE, SW/SE quadrant of the lake, and not to those zones to the west (Figure 6.1). During the peak recmitment times during spring, summer and autumn, the dominant winds in Lake Illawarra are NE and SW (Figure 6.19). Under these wind conditions, larvae would be either held in a strong current gyre near Bevans Island, or transported to the southem area of the lake or to the north-east region respectively (Figure 6.20). This appears to correlate well with the pattems in the catches for many fish species. For example, during December 1999, catches of Acanthopagrus australis, Rhabdosargus sarba and Girella tricuspidata were concentrated in Zone 5 in the northem section of the estuary (Table 6.3). Southerly and north-easterly winds were dominant during the period from November to January, when recmitment of these species would have occurred (Figure 6.19). The effect of wind dfrection and speed is likely to 282 exert a greater influence on these species as they are considered surface-swimmers (Tmski in prep.). In contrast, wind conditions near Durras Lake are relatively calm for most of the year, except for southerly winds during summer months (Figure 6.21). Combined with the presence of bays and arms acting as a physical barrier, the transport of new recraits is less likely to be influenced by winds than in Lake Illawarra. However, there was still a high degree of similarity in the fish communities from all sections of Durras Lake. A study in the Wilson Inlet (Westem Australia) foimd that when this inlet was closed, estuarine circulation is negligible but, importantly, summer sea breezes and convective cooling are sufficient to keep the estuary mixed (Ranasinghe & Pattiaratchi 1999). Work on the bathymetry of Durras Lake has yet to be conducted, and hence water cfrculation models are not available. However it is likely that when Durras Lake is closed, wind-transport would exert a mixing influence as well, particularly in the shallow entrance and central sections. 6.4.3 Comparisons with large-scale sampling program The results of this study agree with the general findings of the larger spatial and temporal scale study of estuarine fish communities along the south coast of NSW reported in Chapter 3 & 4. ICOLLs displayed a high degree of similarity in their fish communities at small spatial scales from the entrance to central and upper regions. There was also a lack of consistent pattem in distribution and settlement of new recraits. Three of the lakes studies previously (Chapter 4), Lake Illawarra, St Georges Basin and Lake Conjola, showed some dissimilarity in the entrance fish fauna compared to the rest of the lake, as was the case for Durras Lake and 283 AM PM AM PM May 1999 November 1999 ^ 133= June 1999 January 2000 July1999 Febraary 2000 August March 1999 2000 September April 1999 2000 October May 1999 2000 Calm 1-10 11-20 21-30 31-40 >«! o40%cata » Figure 6.19: Monthly summaries of wind speed and direction for Lake Illawarra (station no. 068228) from May 1999 to May 2000. Data courtesy of Bureau of Meteorology. Insufficient data was available for December 1999. 284 mmmmsrmvLt amrULATim mywrn'mBtmLf mm-^mYm am^M,*,nm ^ ^ ^^^ C ¥:¥- Figure 6.20: Simulated circulation patterns for common prevailing winds at Lake Illawarra (from Sherman et al. 2000). 285 November May 1999 =^^ 1999 June 1999 =( ) December V 1999 July 199 January 2000 August Febraary 1999 2000 September d J March 1999 /V\ 2000 October April 1999 2000 May O__ iktm h atim«-ie ii» Figure 6.21: Monthly summaries of wind direction and speed for Durras Lake (station no. 069134) from May 1999 to May 2000. Data courtesy of Bureau of Meteorology. Only AM data available. 286 Lake Illawarra in this study. Overall, the entrance region for some ICOLLs separated for to two reasons. Firstly, there was a high species diversity but a large number of these species were marine sfragglers that were sporadically caught in exfremely low numbers. Altematively there was a low species diversity and abundance as a result of the changing hydrological conditions at the entrance region, causing considerable variability in the quality of seagrass beds as potential nursery habitat. In this study, the seagrass beds in the entrance of Durras Lake changed in area quite considerably, not only due to increased water levels as a result of entrance closure, but also due to the artificial opening. The latter obviously caused changes in water current speed and strength in this zone. The changing and dynamic nature of the entrance region in Durras Lake and in other ICOLLs (e.g.. Lake Conjola), and the resultant impact on fish communities highlights the need for protection measures involving a local decision making process. Also, as Lake Illawarra has shown in this study, areas other than the enfrance within the lake, may receive high numbers of new recraits. This may depend on the extent of entrance shoaling influencing the penetration of ocean waters into the estuary, and also the pre-dominate wind conditions at the time determining water cfrculation pattems, indicating that protection of nursery habitats of marine species may need to also focus beyond the entrance regions of estuaries. 6.4.4 Conservation and management implications The results from this study and previous research on ICOLL fish communities (Chapters 3-5) lead to questions of appropriate samplmg design for the monitoring of the health of fish populations in ICOLLs. The pattems noted in this study support conclusions of fish 287 community dynamics of ICOLLs made in Chapter 3 and Chapter 4. Thus, quarterly sampling in regions within the estuary appear to be sufficient for a general indication of community health. A long-term monitoring program, similar to the one conducted in Chapter 3, should provide a comprehensive indication of fish community health, and on-going monitoring would help infer the influence of the opening and closing regime over a long time frame. Such information is essential for the development of the concept of estuarine health and to understand the dynamics of ICOLL envfronments in south-eastem Ausfralia. However, for information conceming recraitment pattems and detailed life history information on fish species exploited by commercial and recreational fisheries, a more frequent temporal sampling program is needed. A more intensive sampling program is requfred to determine exact recraitment times for fish species, and to determine consistency of pattems between years. The sampling design may also be dependent on particular species. For example Smith (1999) recommended sampling at intervals of 1 week for determination of recraitment times for Rhabdosargus sarba. The relatively homogeneous fish communities around the perimeter of these estuaries has important consequences for the management and conservation of these envfronments. The entrance region of estuaries has previously been heralded as an important recraitment area for ocean-spawning species of commercial interest, and hence would be of priority for protection (Hannan & Williams 1998). However, for these particular ICOLLs, this conclusion did not often hold trae. The entrance regions were often quite inconsistent in terms of their overall importance as nursery areas. Other areas within the lakes often had higher recraitment compared to the entrance sites, but it was also difficult to predict which sites would have consistently high recraitment. 288 The inconsistent pattems of settlement within these two estuaries, and across a larger number of estuaries (see Chapter 4 and 5), imply the influential role of localised conditions. The zoning of the estuarine envfronment for various management goals has grown in prominence in the past few years, mainly as a result of the introduction of a national representative system of Marine and Estuarine protected areas (MEPA) for Australia (McNeill & Fairweather 1993; Anon 1998). The primary focus of MEPAs or "priority areas" is the maintenance of biodiversity and to fiilfill conservation criteria (Kelleher & Kenchington 1992). However, most MEPAs are not solely created for conservation purposes but to resolve conflicts between competing demands. Thus multiple use MP As must generate wealth from the sustainable management of activities such as fisheries and tourism, while aiming to complement the conservation needs of that environment. Decisions conceming selection criteria to establish conservation priority areas therefore remains inherently complex. In NSW the zoning plans for Marine Protected Areas incorporate four generic zone types for operational management; sanctuary zone (fiiU protection), habitat protection (protection to habitat but taking of specific fish and plants is allowed), general use (multiple use) and special purpose (protection of Aboriginal or cultural features or marine facilities) (Marine Parks Authority 2001). In many estuaries, where there is an obvious delineation of the fish community along an estuarine gradient, the protection of nursery areas will be on the basis that different areas in the estuary support distinct fish communities. Hence protection of distinct areas throughout the estuary should be sufficient to protect biodiversity. However, for the ICOLLs studied here, the high degree of similarity in the fish communities around the estuaries, coupled with inconsistent pattems of settlement and high variability in pattems of species diversity and abundance questions if a random selection of areas will be 289 enough to protect biodiversity and important nursery habitats. (Bell et al 1988) concluded that seagrass beds in all areas of an Ausfralian estuary were used as a nursery habitat, and conservation measures should include as many beds as possible within an estuary to cater for all species. Given the relatively small size of ICOLLs in southeast Australia, it seems it would be a difficult management problem to delineate and police a number of small sanctuary zones in these estuaries. The situation for protection of estuaries in the Batemans Shelf Bioregion is very different to other marine and coastal areas that will receive protection in NSW, such as rocky shores, and the larger Marine Protected Areas (MPAs) such as Jervis Bay and the Solitary Islands. The main difference is the size ofthese areas. For example Jervis Bay MPA covers an area of approximately 22,000 hectares and Solitary Islands an area of 17,000 hectares (Marine Parks Authority 2002). The size of the estuaries in question for inclusion in a representative system of MP As ranges from 10k-40km (West et al 1985). It has been advocated that these estuaries will be delineated and managed on the four zone types as applied to the Jervis Bay MPA and Solitary Islands MPA (NSW Fisheries 2001b). Hence, given the small size of these ICOLLS, the area contributed to a sanctuary zone (i.e., the marine reserve component or full protection) would be a very small area, and it is doubtfiil that such an area would have any noticeable benefits to conservation of biodiversity and/or fisheries enhancement. It is also being increasingly recognised within the scientific community that ftjU protection, rather than partial protection is critical to achieve the fiill range of benefits that marine reserves can offer (NCEAS 2001). From the results of the research presented here on the fish community dynamics of ICOLLs in SE Australia it is 290 recommended that for a comprehensive and decisive conservation strategy a "whole of estuary" approach for ICOLL conservation management is required. 291 Chapter 7 Conclusions and Recommendations 7.1 Introduction This chapter discusses the major findings of this study, particularly in respect to the conservation of estuarine fish communities in southeast Ausfralia. Management implications for estuaries in this region are also discussed and fiitureresearc h dfrections are proposed. 7.2 Large-scale and small-scale spatial and temporal variability in diversity and abundance of fish in seagrass beds One objective of this study was to compare large-scale and small-scale spatial and temporal variability in fish species diversity and abundance, and this research program represents the first detailed multi-scale study of the shallow water seagrass fish communities in ICOLLs of southeast Australia. It has provided comprehensive information on estuarine fish biodiversity for the region south of Wollongong to Merimbula, a sfretch of coastline approximately 500 km long. Major findings • There were no clear pattems to the variability of species diversity and abundance, spatially and temporally within the ICOLLS, and between them. • There was no decline in species diversity with increasing distance from the estuary mouth, as has been found in other estuarine systems. • For the seven ICOLLs studied there was a notable lack of consistency in pattems of abundance and diversity, both within estuaries and among them. 292 • Weak seasonal pattems were also noted in the fish assemblages, largely as a result of the samples taken in spring, summer and autumn exhibiting similar numbers of fish species, compared to the wmter samples, the latter often having low fish species diversity. 7.3 Seagrass fish communities in S£ Australia and pattems in the species assemblages within and between estuaries Another objective of this research was to assess the fish community assemblage of ICOLLs, and to investigate large- and small-scale pattems in fish community stracture. In terms of fish community stmcture, a feature of the shallow water seagrass fish fauna of the south coast estuaries was the occurrence of a group of species that were common and abundant throughout the estuaries (Chapter 4), which were termed the "core" group of species Majorfindings • An important finding of this study was a high degree of similarity in the assemblages of fishes within the estuaries and among them. The entrance, cenfral and upper locations in each estuary were characterised by small differences in faunal compositions, but there were many species that were common to all sites. The largest degree of dissimilarity between locations within estuaries was not due to the presence/absence of particular species but rather was the result of differences in catches of highly abundant 'shared' species. 293 7.4 Recruitment patterns of commercially and recreationally exploited fish species within ICOLLs along the southeast Australian coastline. This study represents the first comprehensive multi-scale analysis of the recraitment of commercially and recreationally important fish species south of the Sydney Basin. The recmitment strength and timing of five species over a three year period within seven estuaries were examined in detail. These species were: Acanthopagrus australis, Girella tricuspidata, Meuschenia trachylepis, Monacanthus chinensis and Gerres subfasciatus. Overall, for this section of the south-east coast of NSW the recraitment period of the species was profracted but recraitment times were consistent with periods recorded previously for cenfral NSW. Some of the species exhibited latitudinal differences in the timing of their peak recraitment events. Majorfindings • The distribution of postlarvae and juveniles within the estuaries revealed a complex picture in terms of settlement, and in terms of the differences in recmitment sfrength among estuaries. There was no clear pattem to the settlement of individuals within estuaries, not only on the spatial scale of locations within estuaries but also between seasons within years. • Significantly, his study highlighted the variable nature in the sfrength of recraitment, especially on a yearly scale. Over the three years of this research, a major increase in recmitment occurred in the second year (1998), and was evident for most commercial species, occurred in all estuaries and over an extended period. This suggests extemal cues such as climatic factors (e.g., rainfall, wind pattems) were an important factor in the spawning of many fish species. It was suggested that spawning and recmitinent of fish populations of southeast Ausfralian coastline may have been influenced by the effects of 294 El Nino, particularly the above average rainfall in NSW during 1998, and the onshore transport of surface ocean waters. 7.5 Major Conclusions There are some significant outcomes arising from this intensive three-year study of the fish assemblages in the seagrasses ofthese SE Australian ICOLLs, which are outlined below. Firstly, the factor of location within these estuaries is only sometimes an influence in the stmcturing of the fish communities. The relative importance of location within an estuary appeared to be dependent on very localised factors, such as the condition of the entrance, entrance orientation, shape, depth and size of the estuary. The manner in which these localised factors changed over time differed between estuaries. Local climatic variables also played a role in how influential location was within estuaries. For example, wind direction and speed appeared to play a major role in water movements, especially in shallower estuaries, and hence probably affected the transport and settlement of new recmits. Secondly, the effect of year was greater than that demonsfrated by seasonal changes. This was particularly evident for those ICOLLs that were closed to the ocean for long periods of time. However, even in estuaries that were open to the ocean for the entire three year period, aimual changes in the fish community stmcture were more pronounced than seasonal changes. This indicates that recraitment failure or success, or longer term climatic variables than those produced seasonally, are having the largest effect on the stracture of the fish assemblage. Lastly, it was shown that individual local estuarine processes were having a greater effect on fish community stracture than more general geomorphological features. This finding has 295 direct consequences for the current management practices and conservation procedures for ICOLLs in SE AusfraUa. 7.6 Management and Conservation Implications Two principal mechanisms that have been suggested to improve the management regime of ocean and coastal ecosystems are the infroduction of a national representative system of marine protected areas to conserve biological diversity and the use of biological indicators to monitor ecosystem "health". Marine and Estuarine Protected Areas (MEPAs) The delineation of Australia's coastal and marine environment into biogeographic regions has been underway since the infroduction of the Ocean Rescue 2000 marine conservation program by the Commonwealth government (Anon 1998). The NSW coastline has been divided into five bioregions on the basis of distinct physical and biological properties. These bioregions are Manning, Tweed-Morton, Hawkesbury, Batemans Shelf, and the Lord Howe Island Province. A process of selecting estuarine protected areas for the Batemans Shelf bioregion, which is located from the south of Wollongong to the NS WA^ictorian border, has been undertaken (NSW Fisheries 2000). Geomorphological type of the estuary and degree of maturity was used for the determination of "comprehensiveness" and "representativeness" on the basis that the ecology of an estuary is largely dependent upon these general factors (Roy et al 2001). The use of such broad features to select MEPAs highlights the obvious lack of information on the biodiversity and ecological processes for any of the estuaries located in the Batemans Shelf bioregion. However, the results obtained from the present research program have shown that local processes rather than differences in geomorphology are more important influences on the 296 stracture of shallow water fish communities. The use of such a generic level of classification (e.g., based on geomorphology) in selection of a reserve system is not supported by the present study, which highlighted the importance of local factors in stracturing estuarine fish communities in SE Ausfralia. Thus, while six of the seven estuaries in this study are classified as the same geomorhoplogical type, there is no consistency to pattems of fish diversity and abundance, or to the dynamics offish community stracture and all have varying levels of recraitment of different species. The exclusion of biological diversity and ecological processes in the reserve selection process can lead to the non-representativeness of habitat protection that has highlighted the previous ad-hoc procedure for selection of MEPAs in Ausfralia (McNeill 1994). At present, the lack of procedures in selecting MEPAs in NSW indicates a lack of commitment in utilising marine reserves as a serious management tool. This is fiirther reinforced by the present management priority aimed at a buy-out of commercial fisheries licenses in selected estuaries for the creation of recreational fishing havens, rather than for reserves. The declaration ofthese recreational fishing havens does not add to the area of NSW coastal waters protected within marine sanctuary zones. At present only 2.4% of the NSW coastal waters are in complete protection from human activities. The majority of this area occurs in only two locations, Jervis Bay Marine Park and the Solitary Islands Marine Park (Anderson 2003). It is recommended that estuarine nursery habitats need to be included in areas as marine sanctuary zones. This research also has implications for the selection procedure of marine protected areas and the creation of zoning schemes. The study of recraitment pattems indicated that it would be very difficult to consistently predict areas within these ICOLLs which would receive the highest number of new recraits. Areas that act as population sinks by consistentiy receiving large number of recraits should be afforded a high level of protection as they provide a consistent source of recraits to adult populations, and increase the chance of survival of 297 individuals at a critical stage in their life history (Norse 1993). For the ICOLLS of south- eastem Australia, there were no areas that consistently received high numbers of recraits on a spatial and temporal scale, and this findings suggest that a "whole of estuary" approach to management is needed. The investigation of the rarity of estuarine fish species captured during this study came to the conclusion that the majority of species that had low area of occupancy and/or low abundance were species that were not associated with seagrass habitat for their survival. Most of the 'rare' species were species that were marine visitors and/or are more commonly associated with other habitats such as inshore coastal reefs or sand habitats. However, some species did warrant concem over their conservation status, in particular several species from the Monacanthidae family and the pipefish, Sygnathoides biaculeatus. It is recommended that research on the habitat usage and life history characteristics is needed for species belonging to the Monacanthidae family, especially given the decline in fishery stocks of leatherjackets in NSW. The present research has shown that for estuarine fish communities in southeast Ausfralia, the use of rare species is not a usefiil criteria for conservation value in the selection procedure for a representative system of marine protected areas. However, the use of fish assemblages as surrogates of biological diversity shows promise for selecting areas for protection. Surrogate approaches involving reserve selection algorithms for marine systems have been applied to individual, intensively sampled systems, most notable Jervis Bay in NSW. The ecological surveys of Jervis Bay have resulted in one of the most comprehensive existing datasets for a coastal system. Simulations of reserve selection using the Jervis Bay dataset have investigated ecosystem-level surrogates for representation of biodiversity (Ward et al 1999) and differing levels of taxonomic resolution to select representative areas (Vanderklift 298 et al 1998). These studies highlighted that determination of the target level of representation (i.e., the percentage of area that is to be afforded the highest level of protection as the "sanctuary zone") is a critical factor as it will influence the choice of surrogate. (Ward et al 1999) showed that, depending on what percentage of a reserve is to be declared a core conservation area, such as 10, 20 to 40%, will determine how effective a surrogate will be in representing biological diversity. For example, their analysis showed that for a reservation goal >= 10%, fish or invertebrate assemblages were the best surrogates as they included most taxa in a selected area. However, if the goal is >=40%, selection of precise locations based on habitat categories were more appropriate. Reservation goals of 40% are unlikely to be achievable, and recent research indicates that a minimum of 15-20% of a reserve should be a core conservation goal (Roberts & Polunin 1993; Bohnsack 1996; Allison et al 1998; Lauck et al 1998; Fogarty 1999; Roberts 1999). Thus, the current procedure in the Tweed-Morton bioregion of using habitat categorisation as the principal surrogate guiding the selection of MEPAs (Avery in prep.) is a first step in a systematic approach to marine protected area planning. However, the validity of using habitat level information to select areas for a representative marine reserve network needs further investigation. The data from this research is well suited for investigation of the usefulness offish biodiversity information as a surrogate for biological diversity in ICOLLs. Monitoring Estuarine Health The absence of an overarching framework for the management of marine ecosystems is seen to increase the risk of conflict between the resource industry sector and environmental and conservation issues, and lead to ineffective management and protection of the ocean and estuaries (McNeill 1994). For an efficient and encompassing framework for managing coastal ecosystems, many countries worldwide including Ausfralia, England and Canada, are 299 implementing a national "State of the Environment" (SoE) reporting mechanism to document the effects of human uses on ecosystems (Griffith 1997; Ward et al 1998). The inclusion of indicators that monitor and assess the changing condition or health of an ecosystem by measuring key environmental and biological parameters is regarded an essential component of an ecosystem management regime (Sherman 1994). The infroduction of regular national SoE reports are an outcome of the National Strategy for Ecologically Sustainable Development (Anon 1992). Relating more specifically to the conservation and management of the marine biological diversity, the Ausfralian government released its "National Oceans Policy" in 1998 (Anon 1998). An important contribution to the ecosystem-based framework outlined in the National Oceans Policy, will be the national level monitoring provided by SoE reporting through the use environmental indicators (Ward 2000). The data provided by the key set of indicators will detail significant trends and impacts on estuarine, coastal and marine ecosystems. The monitoring of fish populations comes under Class 3: Habitat Quality in the list of Draft Indicators for national State of the Environment reporting (Ward et al. 1998), which relies on species or assemblage-level information and requires detailed biological information for major habitats to be monitored closely. For the estuarine environment, sampling of fish populations in shallow-water seagrass beds has considerable potential as an indicator of estuary health. Sampling fish populations fiilfill some of the extensive properties that Ward et al. (1998) suggest SoE indicators should consist of; for example: capable of providing statistically verifiable, and reproducable data to show frends over time; cost-effective to be monitored regularly and with ease; applicable to large regions; and, able to provide early waming signs. Fish populations also reflect a highly valued aspect of the environment as they are of economic value to commercial and recreational fisheries, and have a high pubUc value. Hence the monitoring of fish 300 communities in seagrass beds has relevance to policy and management needs. This study has shown that the s^npling of shallow water seagrass fish communities has several advantages as a management tool for monitoring of estuary health and their fish populations. Ffrstiy, the power analysis of our experimental design (Chapter 3) showed that a statistical power of 80% and effect sizes of approximately 30% could be achieved with the sampling design that was applied for the large-scale project, thus producing statistically verifiable data. The simple cost-benefit comparison also indicated our design to be the most cost effective, especially for a long-term monitoring program. Most importantly such a sampling design is easily reproducable, allowing comparisons throughout time. The fishing gear, number of replicates and the time-frameo f sampling (quarterly) caught a good selection of fish species and a large number of fish. It was found that this sampling design could detect community changes in the fish populations. The sampling detected changes in recraitment among years, most importantly the high recraitment period of 1998, and subsequent low recraitment periods or recraitment failure of many economically important nearshore species. Changes in the community abundance stracture were easily detected by this method. For example, the large decrease in numbers of non-commercial species, such as gobies and hardyheads, following the rise in recraitment of commercial species. The sampling design also easily distinguished fish community stracture between a lake that had been closed for several years, Coila Lake, and lakes that had more regular access to the sea. This research has provided the groundwork for implementation of a monitoring program of ICOLLs in SE Ausfralia using shallow water fish communities, and the subsequent use of these data in a continuing assessment of estuary and fish community condition or health. For example, at present a major management issue is the presence of Caulerpa taxofoila in the estuaries of Lake Conjola and Burrill Lake (NSW Fisheries 2003), which have caused major changes in the area of seagrass habitat. The 301 research described here has provided an excellent baseline database on the biodiversity and stracturing of the shallow water seagrass communities and can now be used in monitoring program to investigate before/after effects of a major impact or development. The high spatial and temporal sampling undertaken in Chapter 6 supported the findings of Chapter 4, and thus gave an indication of the appropriate scale of a monitoring program. It is recommended that quarterly temporal sampling of ICOLLs will give a detailed picture of fish community dynamics in these estuaries, and would be a valuable tool in monitoring the health of these environments. On a finer scale, sampling in winter could be omitted due to poor diversity and abundance of fish species that was consistently caught during this time. Even though there was a high degree of similarity of the fish community around the various regions of these estuaries, it is nevertheless advocated that sampling should occur in several areas of the estuaries given the lack of consistent pattems in fish diversity and abundance within and among estuaries. In terms of fisherymanagement , the temporal scale of sampling that occurred in this study (Chapter 3 & 4) would also be sufficient to describe general recraitment information for species that are commercially harvested. For example, in this study, temporal changes in the sfrength of recraitment between years were noted for a number of species. Most notably a major recraitment peak in 1998 for most species was evident, as was poorer recraitment in the following year. Such information would be valuable for long-term management of fisheries and may provide an early waming sign of recraitment sfrength. However, for detailed life history information of an individual species it is apparent that sampling on a finer temporal scale would be required. ICOLL management A major concem in the management of ICOLLS is the use of artificial opening of the enfrance mouth. It is a common practice in NSW to open the enfrances of these lakes 302 artificially (Healthy Rivers Commission of New South Wales 2002), and at present there is no understanding of the ecological effects that such manipulations have on the fauna and flora within these estuaries. On a basic level, it allows the recraitment of fish into these estuaries, but management of these systems needs to go beyond economic concems conceming fish and prawn recraitment for commercial and recreational fishes. The are multiple current statutory arrangements governing enfrance openings and include the Crown Lands Act 1989, State Environment Planning Policy 35 - Maintenance Dredging of Waterways, Environment Planning and Assessment Act 1979, Fisheries Management Act 1994 and the Water Management Act 2000 (Healthy Rivers Commission of New South Wales 2002). Despite the broad range of confrols, the NSW Coastal Lake Inquiry (Healthy Rivers Commission of New South Wales 2002) found that there was a failure to undertake assessments under the environmental planning or Crowns land legislation for entrance management works, management procedures were often ad-hoc, and there were no assessments or monitoring of the impacts of opening on lake ecosystems (Healthy Rivers Commission of New South Wales 2002). Management of estuarine environments in NSW is sfrengthened by a number of policies, such as the NSW Coastal Policy, and the recognition by several State government agencies (e.g., Department of Land and Water Conservation and NSW Fisheries) that the natural opening regime ofthese ICOLLS should be maintained where possible. Estuary management in NSW is also becoming an increasingly localised process. The NSW Estuary Management Program is executed through the preparation and implementation of sustainable estuary management plans. This process is carried out by the NSW Department of Land and Water Conservation, with significant community consultation and input from local councils. This study has highlighted that fish community dynamics are closely linked to the unique hydrological and morphological conditions of each ICOLL. Hence, the management ofthese 303 estuarine environments particularly warrant a localised process, and this study is a sfrong case for the benefits and continuation of a whole of catchment management approach. This study also highlights the need for data collection for individual estuaries, rather than the idea of collecting information from a few estuaries and applying a general rale to all. Adherence to the controls in place for artificial entrance openings would also be enhanced by a localised process, where there are opportunities for education, not only on the procedures and assessments that need to be undertaken for entrance management works, but most importantly to educate the community on the unique characteristics and sensitive envfronments ofthese coastal lakes. The management of coastal lakes and their catchments in NSW also comes under the framework of the Coastal Lakes Strategy (Healthy Rivers Commission of New South Wales 2002). The sfrategy has been designed to reinforce current planning and policy development and decision making processes that have implications for coastal lakes in NSW. Such processes include the Comprehensive Coastal Assessment, declarations of national parks, classifications of water bodies under the Water Management Act 2000, reviews of regional forestry agreements and declarations of recreational fishing havens. This is an important sfrategy as it uses a classification scheme to identify a set of goals for each lake, and the selection and use of management tools most appropriate to implementing the actions. The basis of the classification scheme is the degree of natural sensitivity, current condition of the waterbody and catchment, and other significant socio-economic factors. There are four classes in the scheme, comprehensive, significant protection, healthy modified and targeted repair, and the lakes studied in this research program have been classified as follows; Comprehensive Protection - Durras Lake; 304 Healthy Modified - Burrill Lake, Coila Lake, Merimbula Lake, St Georges Basm, Wallaga Lake; Targeted Repair - Lake Illawarra. Within each of these classes, there are outcomes and goals, and the classes of comprehensive protection and significant protection are the only ones that entail some type of conservation measure. However this existing policy of only protectmg pristine or near pristine estuaries in southem NSW is fundamentally flawed. For example. Lake Illawarra has been placed in the "Targeted Repair" category, due to the high degree of disturbance of its catchment and foreshore, and continuing community debate of the condition of the entrance. As a result, there are no protective measures and conservation policies designated for Lake Illawarra (Healthy Rivers Commission of New South Wales 2002). However, Lake Illawarra has one of the highest fisheries production levels of all the estuaries in the region, and has the largest area of the seagrass Zostera capricomi. This estuary is probably contributing more as a fish nursery habitat than most other estuaries in the region. On the other hand, Durras Lake was shown in this study to have a much lower level of fish recraitment than Lake Illawarra, and has less area of seagrass, and hence nursery habitat than Lake Illawarra. Despite this, it has been targeted for conservation (Healthy Rivers Commission of New South Wales 2002). The concept that lakes that are heavily disturbed are of no conservation value needs re-evaluation, if fish populations are to be considered in the process of conservation management. This once again highlights the danger of using over-riding and generic classification systems, such as geomorphology or degree of catchment and lake usage, as surrogates for ecological processes and real data, in conservation management planning. Overall, this study has provided the first overview of the spatial and temporal variability, and community dynamics, of fishes associated with shallow water seagrass habitats in SE 305 ICOLLs, The scale and mtensity of this research has led to many significant findings in relation to these fish species and their communities. 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