Marine Biophysical Assessment of Black Bream and Estuary Perch

Fisheries Adaptation to Climate Change – Marine Biophysical Assessment of Black Bream and Estuary Perch

Greg Jenkins and Daniel Spooner

August 2012

Fisheries Victoria Research Report Series No. 54

Biophysical Assessment of Black Bream and Estuary Perch

If you would like to receive this Author Contact Details: Name: Greg Jenkins information/publication in an Fisheries Research Branch, Fisheries Victoria accessible format (such as large PO Box 114, Queenscliff Vic 3225 print or audio) please call the Authorised by the Victorian Government, Customer Service Centre on: 1 Spring Street, Melbourne 136 186, TTY: 1800 122 969, Printed by DPI Queenscliff, Victoria or email Published by the Department of Primary [email protected] Industries. © The State of Victoria, Department of Primary Copies are available from the website: Industries, 2012. www.dpi.vic.gov.au/fishing This publication is copyright. No part may be General disclaimer reproduced by any process except in accordance This publication may be of assistance to you but with the provisions of the Copyright Act 1968. the State of Victoria and its employees do not guarantee that the publication is without flaw of Preferred way to cite this publication: any kind or is wholly appropriate for your Jenkins G. P., and Spooner, D. R.. (2012) Fisheries particular purposes and therefore disclaims all Adaptation to Climate Change – Marine liability for any error, loss or other consequence Biophysical Assessment of Black Bream and which may arise from you relying on any Estuary Perch. Fisheries Victoria Research Report information in this publication. Series No. 54. 41 pp. ISSN 1448‐7373 ISBN 978‐1‐74326‐265‐8 (Print)

Biophysical Assessment of Black Bream and Estuary Perch ii Executive Summary

Black bream and estuary perch are two of the key recruitment of estuary perch between the Snowy estuarine fish species for fishing in Victoria. This and Glenelg estuaries. On the other hand, local‐ report builds on a previous study of black bream scale influences were suggested by the fact that in Gippsland Lakes to investigate the other estuaries showed unique recruitment relationship between recruitment of these species patterns, an example being the Hopkins estuary and freshwater flow and salinity stratification in for both species. The results clearly showed that a range of Victorian estuaries. The aim is to look recruitment patterns for black bream and estuary for general patterns in these relationships that perch are substantially different across the can be used as a guide to future population estuaries studied. trends in these species under climate change. The In general, strong recruitment of black bream results are used to make recommendations to was associated with years of well developed managers in regard to improving the resilience salinity stratification in the estuary over the and adaptation of these species and fisheries to spring spawning season. In most estuaries the climate change. stratification was associated with reduced The study was conducted in estuaries in western freshwater flow, although there were exceptions Victoria; the Glenelg, Surry, Fitzroy, Eumeralla such as the Eumeralla estuary where strong and Hopkins, was well as the Snowy estuary in stratification was associated with increased eastern Victoria. Data on salinity stratification freshwater flow. In contrast to black bream, with depth were available from three sites within recruitment of estuary perch tended to be higher each of the western estuaries for the period 2003 in years of increased freshwater flow and – 2010, and freshwater flow data were available reduced stratification over the spring spawning for all the rivers entering these estuaries. Black season. bream and estuary perch were sampled by mesh A re‐assessment of previous results from and seine net in 2011 and 2012 so that Gippsland Lakes in the light of the present study recruitment estimated from age structure could suggested a possible two‐phase mechanism, with be compared with salinity stratification and highest recruitment occurring when relatively freshwater flow. Black bream were sampled from low freshwater flows in the spring spawning all estuaries while estuary perch were sampled season were followed by higher flows in the from the Glenelg, Hopkins and Snowy estuaries. following year, which expanded the habitat for Additionally, existing age‐structure data from young juveniles into the broader lakes area. research and diary angler sampling was used to increase the length of the time series for A key result from this study is that two comparison of recruitment variation with important estuarine fish species with high levels freshwater flow. of recruitment variability and similar spawning periods have almost opposite requirements in Freshwater inflows into the estuaries studied terms of freshwater flow and stratification for were relatively similar over the past 30 years, successful recruitment. As a result of this reflecting broad‐scale patterns of rainfall over divergence in environmental requirements it is Victoria. In contrast, characteristics of salinity clear that significant inter‐annual variability in stratification varied widely amongst the the flow regime is required to support both estuaries, reflecting the interaction of inflows species. with the topography and bathymetry of the estuary, and also the estuary mouth opening Climate change is likely to lead to a significant characteristics. reduction in freshwater flows in Victoria, and most of this reduction will occur in spring. Based Both black bream and estuary perch showed on the results of this study, black bream will be highly variable recruitment in this study. The favoured in most systems by lower flows over influence of broad‐scale climatic factors such as the spawning period leading to salt wedge rainfall on recruitment variability in these species development and stratification. In the Gippsland was suggested by the similarity in recruitment Lakes, the fact that flows will not be greatly patterns for black bream in the three most reduced in the autumn period should also limit western Victorian estuaries, and the similarity in the negative effects of climate change, although

Biophysical Assessment of Black Bream and Estuary Perch iii the impact of flow events becoming more In the case of black bream in the Gippsland intermittent and intense is unknown. In contrast, Lakes, catchment management will have to take our results suggest that lower flows over the into account that successful recruitment of bream spring spawning period of estuary perch will may require a two‐phase mechanism where have a deleterious effect on the populations in periodically a relatively low flow over the spring most systems. spawning period is followed by a higher flow over the following twelve months. The key to resilience of these species under climate change will be for managers, in particular It is well known that climate change is likely to catchment mangers, to maintain flows and flow result in winners and losers and it appears from variability at similar levels to that which has this study that black bream in Victoria may occurred historically. The results of this study generally be “winners” and estuary perch may be show that there is no single flow level or narrow “losers”. Management will need to focus on range of flow levels that can be set to maintain maintaining natural variability in flows to which resilience of fish species in the system. The these species are adapted. In terms of fisheries resilience of these two species relies on the management, overfishing will tend to decrease maintenance of inter‐annual variability in flows the resilience of fish populations to climate so that suitable conditions of recruitment of both change, and the sustainable management of species will occur frequently enough for fishing may be most critical for the estuary perch populations to be supported. In the case of fishery. estuary perch, it may be critical to ensure that significant flows occur over the spring period in some years.

Biophysical Assessment of Black Bream and Estuary Perch iv Table of Contents

Executive Summary...... iii

Introduction...... 1 Study Species...... 1 This Report...... 2 Objectives...... 2 Outcomes...... 2

Project Design and Method...... 3 Study Area...... 3 Fish Sampling...... 5 Age analysis...... 5 Physical data...... 5 Data analysis...... 5 Statistical Analysis...... 5

Results...... 7 Age Structure...... 7 Black bream ...... 7 Estuary perch...... 7 Freshwater Flow...... 14 Surface and Bottom Salinity...... 14 Salinity stratification...... 14 Recruitment variation ...... 21 Black bream ...... 21 Estuary perch...... 21 Relationship between recruitment variability and physical variables...... 27 Black bream ...... 27 Estuary perch...... 27

Discussion...... 34 Physical characteristics ...... 34 Recruitment of black bream and estuary perch ...... 34 Effects of freshwater flow and stratification on recruitment ...... 35 Re‐assessment of results from Gippland lakes...... 35

Biophysical Assessment of Black Bream and Estuary Perch v Conclusions ...... 37 Potential climate change implications for two important Victorian estuarine fish species ...... 37 Opportunities for improving the resilience and adaptation of black bream and estuary perch to climate change...... 37

Acknowledgements ...... 39

References ...... 40

Biophysical Assessment of Black Bream and Estuary Perch vi List of Tables Table 1. Characteristics of west Victorian catchments and their estuaries in this study (Sherwood et al. 2008)...... 4 Table 2. Dates of fish sampling in Victorian estuaries...... 6

List of Figures Figure 1. Map of estuaries sampled in western and eastern Victoria...... 3 Figure 2 Sites for water quality monitoring in western Victorian estuaries...... 4 Figure 3. Age structure of black bream from the Glenelg estuary sampled by netting (2011–2012) and angling (2008–2010) ...... 8 Figure 4. Age structure of black bream from the Surry, Fitzroy and Eumeralla estuaries sampled by netting...... 9 Figure 5. Age structure of black bream from the Hopkins River sampled by netting (2012) and angling (2006–2010)...... 10 Figure 6. Age structure of black bream from the Hopkins River sampled by angling and from the Snowy River sampled by netting...... 11 Figure 7. Age structure of estuary perch from the Glenelg estuary and the Hopkins estuary sampled by netting...... 12 Figure 8. Age structure of estuary perch from the Hopkins estuary sampled by netting (2010) and angling (07/08 – 09/10), and from the Snowy estuary sampled by netting ...... 13 Figure 9. Daily average freshwater flow from July to December for rivers entering six Victorian estuaries ...... 16 Figure 10. Salinity measurements between July and December at the surface (circles) and bottom (crosses) for the Glenelg and Surry estuaries...... 17 Figure 11. Salinity measurements between July and December at the surface (circles) and bottom (crosses) for the Fitzroy and Eumeralla estuaries...... 18 Figure 12. Salinity measurements between July and December at the surface (circles) and bottom (crosses) for the Hopkins estuary ...... 19 Figure 13. The average difference between surface and bottom salinities for the July to December period for five west‐Victorian estuaries ...... 20 Figure 14. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of black bream in the Glenelg estuary...... 22 Figure 15. Standardised residuals from the catch curve regression of the age structure of black bream in the Surry estuary...... 22 Figure 16. Standardised residuals from the catch curve regression of the age structure of black bream in the Fitzroy estuary...... 23 Figure 17. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of black bream in the Eumeralla estuary ...... 23 Figure 18. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of black bream in the Hopkins estuary ...... 24 Figure 19. Standardised residuals from the catch curve regression of the age structure of black bream in the Snowy estuary ...... 24 Figure 20. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of estuary perch in the Glenelg estuary ...... 25

Biophysical Assessment of Black Bream and Estuary Perch vii Figure 21. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of estuary perch in the Hopkins estuary...... 25 Figure 22. Standardised residuals from the catch curve regression of the age structure of estuary perch in the Snowy estuary...... 26 Figure 23. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (2004 – 2010) in the Glenelg estuary...... 29 Figure 24. The relationship between recruitment of black bream estimated by catch curve residuals and stratification (1995 – 2010) at the upper site in the Glenelg estuary...... 29 Figure 25. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (1994 – 2010) in the Surry estuary ...... 30 Figure 26. The relationship between recruitment of black bream estimated by catch curve residuals and stratification (1996 – 2010) averaged over sites in the Fitzroy estuary...... 30 Figure 27. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (2004 – 2010) in the Eumeralla estuary ...... 31 Figure 28. The relationship between recruitment of black bream estimated by catch curve residuals and stratification (1993 – 2010) averaged over sites in the Eumeralla estuary ...... 31 Figure 29. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (1990 – 2010) in the Hopkins estuary...... 32 Figure 30. The relationship between recruitment of estuary perch estimated by catch curve residuals and stratification (2002 – 2010) averaged over sites in the Glenelg estuary ...... 32 Figure 31. The relationship between recruitment of estuary perch estimated by catch curve residuals and freshwater flow (2004 – 2010) in the Hopkins estuary...... 33 Figure 32. The relationship between recruitment of estuary perch estimated by catch curve residuals and stratification (1990 – 2010) at the lower site in the Hopkins estuary...... 33

Biophysical Assessment of Black Bream and Estuary Perch viii Introduction

It is predicted that climate change will result in prepare fisheries sectors and fisheries managers changes to ocean circulation patterns, water for change. temperatures and sea levels (Poloczanska et al. Under this initiative, the marine biophysical 2007). Climate change is also predicted to cause assessments are aimed at understanding the changes in weather patterns across south eastern biophysical implications of climate change to Australia, leading to reduced seasonal rainfall better inform decision making. These and infrequent high intensity rainfall events, assessments aim to determine the degree of resulting in increased salinity levels. In addition, exposure a species has to climate change to demand for freshwater will result in increased inform assessments on how vulnerable Victoria’s regulation of freshwater flows. fishing and aquaculture sectors are to these The best estimate of rainfall change based on changes. climate modelling under a medium emissions This project builds on and is informed by the risk scenario is a deficit of 2–5% by 2030, increasing to assessment undertaken in 2008/09 and the a deficit of 5–10% by 2070 (Anon. 2007). This desktop review of literature in 2009/10. These change is highly seasonal, with a spring deficit of previous projects assisted in establishing a 20–30% compared to an autumn deficit of 2–5% prioritisation framework for focusing research by 2070 (Anon. 2007). As well as a reduction in regarding climate change implications for fish in overall rainfall, rain will tend to occur in more Victoria. intense events, interspersed with an increasing proportion of dry days, signifying more extreme weather fluctuations (Anon. 2007). In terms of Study Species rainfall effects on runoff and salinity, reduced Black bream was specifically identified as one of runoff and increasing salinity due to decreasing the higher priority species for Victoria. This rainfall will be exacerbated by increased solar species represents a key recreational and radiation and decreased humidity leading to commercial fish species in Victoria that increased evaporation rates (Anon. 2007). This completes its life cycle within an estuarine means that the projected decrease in runoff will environment. This species may also be used as an be in the order of 30% by 2060, and the greatest indicator species for understanding the decease will be in the west of the State (Mills and vulnerability of estuarine fish species in Victoria Womersley 2012). and measures for enhancing the sustainability of estuarine species (Hutchinson et al. 2010). Estuary These physical changes will have implications for perch are another key recreational fish species the biomass and range of marine and estuarine that is estuary dependent (Douglas 2010; Walsh fish and the ecosystems that support them. In et al. 2010). At present, little is known about the some cases these changes will manifest in environmental requirements for successful declines in abundance and distribution, and for recruitment of this species, and how these other species increased abundance and requirements compare to those of black bream distribution. These changes in abundance and (Walsh et al. 2010). distribution mean that management arrangements will need to be responsive to Gippsland Lakes has the only remaining change. commercial black bream fishery in Victoria, and is also considered an important recreational An understanding of the likely implications to fishery for black bream. In Gippsland Lakes it the key Victorian fisheries is necessary to has been demonstrated that salinity stratification adequately prepare for responding to these conditions and freshwater flow in the first year of challenges and to better target management life are critical to recruitment success and year efforts. class strength (Jenkins et al. 2010). The salt wedge Fisheries Victoria is undertaking a suite of provides for a zone of high productivity that projects under the Future Farming Strategy provides food for larvae (Jenkins et al. 2010). In initiative ʺAdaptation of fisheries, aquaculture particular, the presence of a well developed salt and fisheries management to climate changeʺ to wedge in the rivers feeding into the Lakes seems

Biophysical Assessment of Black Bream and Estuary Perch 1 to be critical for larval survival (Williams et al. There are two specific work areas presented in 2012). this report: Information on flow dependencies and salinity • Assessment of the relationship between stratification leading to strong bream recruitment black bream recruitment success and in the Gippsland Lakes has played a role in environmental flows and salinity developing flow recommendations for the stratification in six Victorian estuaries. northern river systems that flow into Gippsland • Assessment of the relationship between Lakes. However, in Victoria there are 110 river estuary perch recruitment success and systems that drain into estuarine environments. environmental flows and salinity These estuaries have varied entrance conditions, stratification in three Victorian estuaries. nutrient inputs, hydraulic retention times, The discussion presented in this report provides bathymetry and water quality (Barton et al. 2008). guidance on importance of environmental flows The reliance of suitable environmental flows and and salinity stratification for black bream and salinity stratification to facilitate successful black estuary perch recruitment across a range of bream spawning and recruitment needs to be estuaries. Where possible this enables us to tested across a broader range of Victorian provide advice on suitable environmental flow estuaries. requirements for maintaining sustainable black The life cycles of other estuarine, euryhaline fish bream and estuary perch populations. species are also likely to be influenced by the The potential changes to these relationships quality and timing of freshwater flows entering under altered patterns of rainfall and other the estuary. Similar to black bream, estuary perch environmental variables under climate change (Macquaria colonorum) are an apex predator in are also explored. Implications for water flow south‐eastern Australian estuaries, and are an and estuarine management requirements, extremely important component of these particularly in areas such as artificial mouth ecosystems (Douglas 2010; Walsh et al. 2010). opening and water abstraction under future Estuary perch are also a species of great interest climate change scenarios, are also considered. to recreational fishers for sport and eating qualities; however to date, little biological and ecological information has been collected for Objectives estuary perch (Walsh et al. 2010). From the 1) To inform decision makers on the limited information available it appears that vulnerability of black bream and estuary environmental flows and seasonal changes in perch to climate change in a range of key primary and secondary productivity are likely to Victorian estuaries. play a key role in the recruitment success rate of 2) Inform opportunities for improving the estuary perch (Newton 1996; Walsh et al. 2010). resilience and adaptation of black bream and Of particular interest to climate change estuary perch to climate change. adaptation is whether the conditions of environmental flows and salinity stratification Outcomes for successful recruitment of estuary perch are similar to, or different from, black bream. 1) Improved understanding of the potential climate change implications for two This Report important Victorian estuarine fish species 2) Informed fisheries and natural resource The work presented in this report builds on the management decisions on managing fisheries outcomes of the biophysical risk assessment and estuarine environments under a (Hutchinson et al. 2010) and the assessment of changing climate. key species (Jenkins 2010) through targeted fish sampling in a variety of Victorian estuarine systems, and collation and analysis of salinity profiles and catchment discharge data.

Biophysical Assessment of Black Bream and Estuary Perch 2 Project Design and Method

hydrological cycle where estuaries are highly Study Area stratified in the summer and autumn with the The primary study area was western Victoria potential for low dissolved oxygen in bottom due to the presence of a range of estuaries waters, followed by increased flows and important for recreational fishing and the reduced stratification and increased dissolved availability of water quality data that included oxygen in the winter/spring (Newton 1996). The depth stratified sampling of salinity. In western Glenelg River had the longest estuary length Victoria, the Glenelg, Surry, Fitzroy, Eumeralla and largest catchment, and was the only and Hopkins river estuaries were sampled regulated river studied in western Victoria (Figure 1). The Glenelg, Surry and Fitzroy (Table 1). Additional samples were collected estuaries are relatively linear, while the from the Snowy River estuary between the Eumeralla has a broad coastal receiving area confluence of the Snowy and Brodribb Rivers (Yambuck Lake) and the Hopkins is relatively and the mouth (Figure 1); however in this case broad in the lower reaches (Figure 2). These only physical time‐series data available was for estuaries tend to be highly stratified and are freshwater flow. The Snowy River flow is highly intermittently closed at the mouth under low regulated near the source at Lake Jindabyne. flow conditions. There tends to be a distinct

Surry River

Figure 1. Map of estuaries sampled in western and eastern Victoria

Biophysical Assessment of Black Bream and Estuary Perch 3

Hopkins River Eumeralla River

Fitzroy River Surry River Glenelg River

Figure 2 Sites for water quality monitoring in western Victorian estuaries

Table 1. Characteristics of west Victorian catchments and their estuaries in this study (Sherwood et al. 2008). Estuary Longitude (E) Latitude (S) Catchment Pop. Estuary Catchment Area (km2) Density Length Water (km‐2) (km) Regulation Glenelg 140° 59’18” 38° 03’36” 12,362 1.11 70 Yes

Surry 141° 42’06” 38° 15’39” 355 1.12 10 No

Fitzroy 141° 51’13” 38° 15’50” 1,435 1.19 13 No

Eumeralla/Ya 142° 02’35” 38° 20’22” 874 0.27 7.8 No mbuk

Hopkins 142° 30’24” 38° 24’14” 9,009 1.1 9.5 No

Biophysical Assessment of Black Bream and Estuary Perch 4 Fish Sampling Data analysis Black bream and estuary perch were sampled Recruitment variability was estimated from the with mesh nets deployed at two sites in each age structure of the sampled bream using catch‐ estuary in early 2011 and 2012 (Table 1). curve regression (the natural log of the number Supplementary samples were also collected with of fish classified to each year class regressed a seine net from the Glenelg and Hopkins against age) following the methods of Maceina estuaries in 2012 to increase the sample size of (1997) and Staunton‐Smith et al. (2004). We black bream. Additional age data came from assumed that deviation from the catch‐curve angler diary and research angler samples from regression was a reflection of variable the Glenelg and the Hopkins collected over the recruitment (Staunton‐Smith et al. 2004), with past decade which had been routinely aged as large positive and negative studentized residuals part of annual stock assessment. representing strong and weak year‐classes respectively (Halliday et al. 2008). Black bream Age analysis and estuary perch were considered to be fully In the laboratory, otoliths of black bream and susceptible to mesh and seine nets by age 1, and estuary perch were dissected from fish and to diary and research angling by age 2. Catch stored dry for ageing. Opaque zones in the curves were therefore calculated from these ages otoliths of black bream (Morison et al. 1998) and for each gear type. estuary perch (Walsh et al. 2010) have been validated as forming annually. Transverse Statistical Analysis sections of otoliths were aged using standard For recruitment estimated catch curve regression, protocols developed at the Fisheries Research correlation and simple and multiple linear Branch, Queenscliff (Morison et al. 1998). The regression was used to examine the relationship method, validation and precision of ageing black between recruitment variability and the bream otoliths is described by Morison et al. environmental variables: water column (1998). In this study the same method was stratification and freshwater flow. Residual plots applied to ageing estuary perch. were examined when undertaking regression analyses to check assumptions relating to Physical data homogeneity of variance, non‐linearity, leverage, The Glenelg Hopkins Catchment Management and outliers (Quinn and Keough 2002). In Authority has been recording depth stratified accordance with the standard ageing method, the measurements of physical and chemical variables estimated year class to which an individual fish in western Victorian estuaries at approximately belonged is normally estimated as the year that monthly intervals since late 2003. The three the first increment was formed. However, for sample sites closest to the estuary mouth were both black bream and estuary perch, this is likely analysed (lower (site 3), mid (site 2), upper (site to have occurred at approximately 12 months 1) (Figures 1,2). after spawning (i.e. spawning occurs in spring Surface and bottom salinities were averaged for and the first increment is formed the following sampling times for the months of July to spring). Therefore, when analysing the possible December (the approximate spawning season). effects of freshwater flow and stratification on An index of water column stratification was then spawning and eggs and larval survival, the estimated by subtracting the average surface estimate of year‐class strength was lagged by one salinity from the average bottom salinity to give year. an annual estimate. Flow (discharge, Ml d‐1) data are recorded for each river system entering the estuaries and are stored at the Victorian Water Resources Data Warehouse (http://www.vicwaterdata.net/vicwaterdata/hom e.aspx). Daily flow data over the period of the present study were extracted and annual averages were calculated for the July to December spawning period.

Biophysical Assessment of Black Bream and Estuary Perch 5

Table 2. Dates of fish sampling in Victorian estuaries. Estuary 2011 2012

Glenelg 17 March 8 February

1 March

Surry 16 March

Fitzroy 29 April

Eumeralla 28 April 7 February (Yambuk)

Hopkins 27 April 6 February

29 February

Snowy 21 February

Biophysical Assessment of Black Bream and Estuary Perch 6 Results

Age Structure Estuary perch Estuary perch age structure sampled by research Black bream netting in the Glenelg estuary showed episodic Black bream showed variable age structure in the recruitment, with most of the fish coming from Glenelg estuary, with a strong year‐class in 2006, the 2008 and 2005 year classes (Figure 7). moderately strong year‐classes in 2003, 2000 and Sampling in 2012 also indicated a significant 1998 (Figure 3). Year‐classes in the most recent cohort of 0+ age recruits (Figure 7). years also appeared to be moderately strong (Figure 3). Age structure of estuary perch in the Hopkins estuary showed high variability but not to the Like the Glenelg estuary, 2006 was also a extent seen in the Glenelg estuary (Figure 7). dominant year class in the Surry and Fitzroy Recent year classes since 2007 appeared to be estuaries (Figure 4). There was a moderate year relatively strong, as were the 2004 and 2005 year class in 2009, and the 2003 and 2000 year classes classes (Figure 7). Older year classes of were also in evidence in both estuaries (Figure 4). significance included 2000 and 1996 (Figure 7). The Surry River was notable for the large number Sampling of estuary perch from the Glenelg prior of 0+ age fish caught in 2011 (Figure 4). to the present study indicated that as well as in 2005, there were significant year classes in 2003‐ The age structure of bream in the Eumeralla estuary showed a different pattern to the three 2004, 1999‐2000 and 1996 (Figure 8). Individuals estuaries to the west, with strong year classes in from year classes from the early to mid 1980s were also present (Figure 8). 2010 and 2005, and moderate year classes in 2009, 2008 and 2004 (Figure 4). Year classes at the end The age structure of estuary perch sampled from of the 1990s were also in evidence (Figure 4). the Snowy estuary by research netting was dominated by the 2008 year class (Figure 8). The age structure of bream from the Hopkins estuary in 2012 showed significant year classes in 2009, 2008, 2005, 2000 and 1999 (Figure 5). Sampling by angling indicated that there was a strong year class in 1999 (Figures 5,6), sampling in 2004 indicated that the 2000 year class was also prominent (Figure 6). Sampling in 2003 indicated significant year classes from 1994 to 1996 (Figure 6) and the presence of older fish from the early to mid 1980s (Figure 6). The age structure of bream from the Snowy River showed a dominance of recent year classes including 2010, 2009, 2007 and 2005, as well as a few older individuals from year classes in the 1980s (Figure 6).

Biophysical Assessment of Black Bream and Estuary Perch 7 40 2012 N=97

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

40 2011 N=69 30

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1 40 0910 N=92

Number of bream of Number 30

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1 60

50 0809 N=116

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

Year class

Figure 3. Age structure of black bream from the Glenelg estuary sampled by netting (2011–2012) and angling (2008–2010) Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 8

40 Surry 2011 N=82

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1 40 Fitzroy 2011 N=62 30

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 0 9 9 9 9 2 2 1 1 1 1 40 Eumeralla 2012 N=98 Number of bream of Number * 30

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1 40 Eumeralla 2011 N=78 30

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

Year class

Figure 4. Age structure of black bream from the Surry, Fitzroy and Eumeralla estuaries sampled by netting.

Biophysical Assessment of Black Bream and Estuary Perch 9

40 Hopkins 2012 N=99 30

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

40 Hopkins 0910 N=35 30

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

40 Hopkins 07 N=31 30 * Number ofbream 20

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

80 Hopkins 06 N=111

0 0 5 0 5 0 5 0 1 0 0 9 9 8 8 0 0 0 9 9 9 9 2 2 2 1 1 1 1

Year class

Figure 5. Age structure of black bream from the Hopkins River sampled by netting (2012) and angling (2006–2010) Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 10

80 Hopkins 05 N=122

0 0 5 0 5 0 10 05 9 9 8 808 0 0 00 9 9 9 2 2 2 19 1 1 1

60 Hopkins 04 N=124

0 0 1 5 5 0 5 0 0 0 00 9 9 8 8 2 0 0 9 9 9 9 2 2 1 1 1 1 Number of bream Number 80 Hopkins 03 N=146

60 *

0 0 1 0 5 0 5 0 0 05 0 9 9 8 8 2 0 0 9 9 9 9 2 2 1 1 1 1

60 Snowy 2012 N=99

0 10 05 0 5 0 5 0 0 0 9 9 8 8 2 0 9 9 9 2 20 1 19 1 1

Year class

Figure 6. Age structure of black bream from the Hopkins River sampled by angling and from the Snowy River sampled by netting Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 11 80 Glenelg 2012 N=99 60

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 2 0 9 9 9 9 2 1 1 1 1 80 Glenelg 2011 N=104 60

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 2 0 9 9 9 9 2 1 1 1 1 * 40

Number of estuary perch Hopkins 2012 N=99 30

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 2 0 9 9 9 9 2 1 1 1 1 40 Hopkins 2011 N=125 30

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 2 0 9 9 9 9 2 1 1 1 1

Year class

Figure 7. Age structure of estuary perch from the Glenelg estuary and the Hopkins estuary sampled by netting Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 12 20 Hopkins 2010 N=38

0 0 5 1 0 0 5 0 5 0 0 0 9 9 8 8 2 0 0 9 9 9 9 2 2 1 1 1 1 20 Hopkins 0910 N=34

0 0 1 5 0 5 0 5 0 0 0 0 9 9 8 8 2 0 0 9 9 9 9 2 2 1 1 1 1 20 Hopkins 0809 N=63

0 0 5 1 0 0 5 0 5 0 0 0 9 9 8 8

Number of estuary perch estuary of Number 0 2 2 0 9 9 9 9 2 1 1 1 1 20 Hopkins 0708 N=80

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 2 0 9 9 9 9 2 1 1 1 1 80

60 Snowy 2012 N=100

0 0 5 1 0 0 5 0 5 0 0 0 0 9 9 8 8 2 2 0 9 9 9 9 2 1 1 1 1 Year class

Figure 8. Age structure of estuary perch from the Hopkins estuary sampled by netting (2010) and angling (07/08 – 09/10), and from the Snowy estuary sampled by netting Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 13 11). Bottom salinities in the Fitzroy estuary were Freshwater Flow variable, with the highest values (between 30 The average freshwater flows from July to and 40) showing an increasing trend through December to the six estuaries varied widely, time at the lower site (Figure 11). Significant with the highest volumes of water entering the pulses of freshwater near the bottom at the Snowy, Glenelg and Hopkins estuaries, and lower site were evident in 2004, 2009 and 2010 relatively low flows entering the Surry, Fitzroy (Figure 11). and Eumeralla estuaries (Figure 9). Flows in all estuaries were generally higher from 1980 to The Eumeralla River at the upper site was too 1995 compared to since 1995, particularly in the shallow for a meaningful comparison of surface larger Glenelg, Hopkins and Snowy Rivers, and bottom salinities. Salinities at the mid site reflecting the extended drought that occurred in rarely exceeded 20 while a wide range of this period (Figure 9). Flows also varied salinities reaching 40 occurred at the lower site substantially on a one to three year scale; for (Lake Yambuk) (Figure 11). Surface salinities example, in the past decade flows in the western were often in the 10 to 30 range, particularly in estuaries were higher in 2000‐2001, 2004, 2007, 2006 (Figure 11). Bottom salinities were and 2009 – 2010 (Figure 9). Flows in all rivers generally high at the lower site with the were significantly correlated amongst each other exception of 2006 and some samples from 2008 (P<0.05). Highest correlations were between (Figure 11). Significant pulses of freshwater near rivers in western Victoria (Pearson’s R = 0.811 – the bottom at the lower site were evident in 2004 0.944) while correlations between flow in the and 2010 (Figure 11). Snowy River and western rivers were lower (R = Surface salinities in the Hopkins estuary were 0.353 – 0.508). variable, generally ranging from just above zero to approximately 30; freshwater at the surface Surface and Bottom Salinity only occurred in 2010 (Figure 12). Salinity in Surface salinities in the Glenelg estuary were bottom waters of the Hopkins estuary was generally less than 10 at the upper and mid sites, typically high, with hypersaline conditions but were much more variable at the lower site, occurring in 2004 (Figure 12). Bottom salinities sometimes reaching above 30 (Figure 10). were generally lower in 2006 and 2007 (Figure Bottom salinities in the Glenelg estuary were 12). Salinities in some bottom samples in 2006 generally between 30 and 40 and were lower were below 20 (Figure 12). The only pulse of from 2006 to 2008 (Figure 10). Bottom salinities freshwater observed in the bottom samples was close to zero, indicating a pulse of freshwater at the upper site in 2010 (Figure 12). throughout the water column, were evident in 2004, 2007 and 2010 (Figure 10). Salinity stratification Surface salinities in the Surry estuary were quite Salinity stratification in the Glenelg estuary was variable, ranging between zero and 30 (Figure quite strong, especially at the mid and upper 10). Surface salinities tended to be lower in 2004 sites (Figure 13). Stratification at the upper site and 2009, while surface salinities in the 10 to 30 showed yearly variation, with peaks in 2005 and range were common in 2005 and 2007 (Figure 2008, and minima in 2004, 2007 and 2010 (Figure 10). Bottom salinities in the Surry estuary were 13). At the mid and lower sites, 2009 was a year also variable, with some hypersaline values of of relatively high stratification (Figure 13). over 40 recorded at the lower site, but a wide Stratification was less well developed in the range of values recorded at the mid and upper Surry estuary compared to the Glenelg estuary, sites (Figure 10). Pulses of freshwater near the particularly at the mid and upper sites (Figure bottom were evident in all years except 2005 and 13). Stratification tended to be relatively 2006 (Figure 10). stronger in 2005 and 2010 and comparatively Salinity in the Fitzroy estuary showed weak in 2009 (Figure 13). significant variation depending on site (Figure Like the Surry estuary, salinity stratification was 11). Surface salinities were near zero with the not strongly developed in the Fitzroy estuary, exception of 2005 and 2006 at the upper site, but particularly at the upper site (Figure 13). The were much more variable at the mid and lower annual trend in stratification was highly variable sites, reaching between 30 and 40 in some years amongst sites although 2005 showed relatively at the lower site (Figure 11). In 2005, surface high stratification at all sites (Figure 13). salinities were always well above zero (Figure

Biophysical Assessment of Black Bream and Estuary Perch 14 In the Eumeralla estuary the salinity in the water column was essentially homogeneous at the mid site, but stratification was highly variable at the lower site (Lake Yambuk) (Figure 13), ranging from moderately strong stratification in 2004, 2007 and 2009/10 to no stratification (homogeneous salinity) in 2006 (Figure 13). Stratification in the Hopkins estuary showed considerable variation amongst years, most notably at the mid site (Figure 13). Stratification was well developed in 2004 and 2009, but was relatively weak in 2006 at the mid site and 2005 and 2006 at the lower site (Figure 13).

Biophysical Assessment of Black Bream and Estuary Perch 15 7000 6000 Glenelg 5000 4000 3000 2000 1000 0 400 Surry 300

200

100

0 400

300 Fitzroy

200

100

0 400

Flow (ML/d) Eumeralla 300

200

100

0 4000 Hopkins 3000

2000

1000

0 12000 10000 Snowy 8000 6000 4000 2000

0 1980 1985 1990 1995 2000 2005 2010 2015

Year

Figure 9. Daily average freshwater flow from July to December for rivers entering six Victorian estuaries Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 16

Glenelg - upper Surry - upper

40 40

30 30

20 20 Salinity

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2011 2004 2005 2006 2007 2008 2009 2010 2011

Glenelg - mid Surry - mid 40 40

30 30

20 20 Salinity

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2011 2004 2005 2006 2007 2008 2009 2010 2011

Glenelg - Lower Surry - Lower 40 50

40 30

20 Salinity 20

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2011 2004 2005 2006 2007 2008 2009 2010 2011 Year Year Figure 10. Salinity measurements between July and December at the surface (circles) and bottom (crosses) for the Glenelg and Surry estuaries Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 17

Fitzroy - upper 40

20 Salinity

0 2004 2005 2006 2007 2008 2009 2010 2011

Fitzroy - mid Eumeralla - mid 40 40

30 30

20 20 Salinity Salinity

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2011 2004 2005 2006 2007 2008 2009 2010 2011

Fitzroy - Lower Eumeralla - Lower 40 40

30 30

20 20 Salinity Salinity

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2011 2004 2005 2006 2007 2008 2009 2010 2011

Year Year Figure 11. Salinity measurements between July and December at the surface (circles) and bottom (crosses) for the Fitzroy and Eumeralla estuaries

Biophysical Assessment of Black Bream and Estuary Perch 18 Hopkins - upper 40

20 Salinity

0 2004 2005 2006 2007 2008 2009 2010 2011

50 Hopkins - mid

30 Salinity 20

0 2004 2005 2006 2007 2008 2009 2010 2011

50 Hopkins - lower

30 Salinity 20

0 2004 2005 2006 2007 2008 2009 2010 2011

Year Figure 12. Salinity measurements between July and December at the surface (circles) and bottom (crosses) for the Hopkins estuary Note different scales of Y axis

Biophysical Assessment of Black Bream and Estuary Perch 19 40 40 Glenelg Surry

30 30

20 20 Stratification

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2004 2005 2006 2007 2008 2009 2010

40 40 Fitzroy Eumeralla

30 30

20 20 Stratification

10 10

0 0 2004 2005 2006 2007 2008 2009 2010 2004 2005 2006 2007 2008 2009 2010

Year

40 Hopkins

30 Lower

20 Mid Upper Stratification

0 2003 2004 2005 2006 2007 2008 2009 2010

Year

Figure 13. The average difference between surface and bottom salinities for the July to December period for five west‐Victorian estuaries

Biophysical Assessment of Black Bream and Estuary Perch 20 2009, 2006, 2003 and 2000 year classes were all Recruitment variation strong (Figures 14‐16). Black bream Catch curve analysis for black bream in the six Estuary perch estuaries showed highly variable recruitment Like black bream, catch curve analysis for (Figures 14‐19). estuary perch in three estuaries showed highly variable recruitment (Figures 20‐22). In the Glenelg estuary, catch curve analysis indicated that peaks in 0+ age recruitment In the Glenelg estuary, catch curve analysis occurred in 2009, 2006, 2003, 2000 and 1998 indicated that peaks in 0+ age recruitment of (Figure 14). A very low level of recruitment was estuary perch occurred in 2008 and 2005 (Figure recorded in 2002 (Figure 14). 20). A low level of recruitment was estimated to have occurred in 2009 and 2007 (Figure 20). Recruitment variation based on catch curve residuals in the Surry estuary indicated high 0+ Recruitment variation based on catch curve age recruitment in 2011, 2006, 2000, 1998 and residuals in the Hopkins estuary indicated high 1996, while moderate recruitment was also 0+ age recruitment in 2008, 2003‐2005, 1999‐2000, indicated in 2009 and 2003 (Figure 15). and 1996 (Figure 21). Recruitment was estimated Recruitment was estimated to be very low in to be very low in 2001‐2002, and moderately low 2004 and 2005 (Figure 15). in 2006 and 1998 (Figure 21). Recruitment of 0+ age black bream in Fitzroy Recruitment variation based on catch curve estuary was estimated to be highest in 2006, and residuals in the Snowy estuary indicated very moderately high in 2008‐2009, 2003, and 1999‐ high 0+ age recruitment in 2008 (Figure 22). A 2001 (Figure 16). Recruitment was estimated to low level of recruitment was estimated to have be very low in 2002 and 2010 (Figure 16). occurred in 2010, and to a lesser extent in 2007 (Figure 22). Recruitment variation based on catch curve residuals in the Eumeralla estuary indicated Recruitment variation based on catch curve high 0+ age recruitment in 2010, 2004‐2005, 1997‐ residuals was compared amongst the three 2000, and 1995 (Figure 17). A low level of estuaries sampled for estuary perch using recruitment was estimated to have occurred in correlation analysis. Recruitment variation was 2002 and 2007 (Figure 17). significantly correlated between the Glenelg estuary and the Snowy estuary (R = 0.786, P = Catch curve analysis of bream age structure in 0.012) but neither was significantly correlated the Hopkins Estuary indicated very strong 0+ with recruitment in the Hopkins estuary (P > age recruitment in 2009 and 1999, and 0.05). The significant correlation between moderately strong recruitment in 2005‐2006, recruitment in the Snowy and Glenelg estuaries 1994‐1995, and 1990 (Figure 18). Relatively low was mainly driven by the dominant 2008 year recruitment was estimated to have occurred in class in both (Figure 20, 22). 1993, 1997, 2003, 2007 and 2010 (Figure 18).

Recruitment variation based on catch curve residuals in the Snowy estuary indicated high 0+ age recruitment in 2009‐2010, 2007, 2005, 2000 and 1998 (Figure 19). A low level of recruitment was estimated to have occurred in 2003 and 2008 (Figure 19). Recruitment variation based on catch curve residuals was compared amongst the six estuaries sampled for black bream using correlation analysis. Recruitment variation was significantly correlated amongst the three most western estuaries (Glenelg versus Surry, R = 0.567, P = 0.043; Glenelg versus Fitzroy, R = 0.661, P = 0.014; Surry versus Fitzroy, R = 0.640, P = 0.019), but recruitment was not significantly correlated amongst other estuary combinations (P > 0.05). In the three western estuaries, the

Biophysical Assessment of Black Bream and Estuary Perch 21 3 2012 2011 2009/10 2 2008/09

-1 Catch Curve residuals Catch Curve

-2

-3

-4 1990 1995 2000 2005 2010 2015 Year-class

Figure 14. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of black bream in the Glenelg estuary

-1 Catch residuals Curve -2

-3 1990 1995 2000 2005 2010 2015

Year-class Figure 15. Standardised residuals from the catch curve regression of the age structure of black bream in the Surry estuary

Biophysical Assessment of Black Bream and Estuary Perch 22 3

-1 Catch Curve residuals Curve Catch

-2

-3 1990 1995 2000 2005 2010 2015

Year-class Figure 16. Standardised residuals from the catch curve regression of the age structure of black bream in the Fitzroy estuary

2011 2 2012

-1 Catch residuals Curve

-2

-3 1990 1995 2000 2005 2010 2015

Year-class Figure 17. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of black bream in the Eumeralla estuary

Biophysical Assessment of Black Bream and Estuary Perch 23 6

2012 5 2010/11 2007 2006 4 2005 2004 3 2003

1 Catch Curve residuals Curve Catch 0

-1

-2

-3 1985 1990 1995 2000 2005 2010 2015

Year-class Figure 18. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of black bream in the Hopkins estuary

-1 Catch Curve residualsCatch Curve

-2

-3 1990 1995 2000 2005 2010 2015

Year-class Figure 19. Standardised residuals from the catch curve regression of the age structure of black bream in the Snowy estuary

Biophysical Assessment of Black Bream and Estuary Perch 24 4

3 2012 2011

Catch residuals Curve -1

-2

-3 1990 1995 2000 2005 2010 2015

Year-class Figure 20. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of estuary perch in the Glenelg estuary

3 2012 2011 2010 2 2009/10 2008/09 2007/08 1

-1 Catch Curve residuals Catch Curve

-2

-3 1990 1995 2000 2005 2010 2015

Year-class Figure 21. Standardised residuals (data points) and average of the residuals (solid line) from the catch curve regression of the age structure of estuary perch in the Hopkins estuary

Biophysical Assessment of Black Bream and Estuary Perch 25 5

0 Catch Curve residuals Curve Catch

-1

-2

-3 1990 1995 2000 2005 2010 2015 Year-class

Figure 22. Standardised residuals from the catch curve regression of the age structure of estuary perch in the Snowy estuary

Biophysical Assessment of Black Bream and Estuary Perch 26 was marginally non‐significant (n = 15, R = ‐ Relationship between 0.452, P = 0.091). In contrast to freshwater flow, recruitment variability and there was a strong, positive relationship physical variables between stratification averaged across sites and recruitment, with nearly 90% of recruitment Black bream variation explained (R = 0.942, F1,4 = 31.393, P = In the Glenelg estuary there was a strong 0.005; Figure 26). There was no improvement to negative relationship between freshwater flow the recruitment variability explained by and the level of stratification at the upper site including freshwater flow and average between 2004 and 2010 (R = ‐0.902, F1,5 = 21.928, P stratification in a multiple regression. = 0.005). Over the same period there was a significant decline in recruitment with In the Eumeralla estuary there was a significant positive relationship between freshwater flow increasing freshwater flow (R = ‐0.546, F1,16 = 6.780, P = 0.019; Figure 23). When the and stratification averaged across sites between comparison with freshwater flow was extended 2004 and 2010 (R = 0.780, F1,5 = 7.790, P = 0.038). back to 1995 using all available recruitment data, Over the same period there was a significant there was still a significant negative relationship positive relationship between recruitment and between freshwater flow and recruitment (R = ‐ freshwater flow, with more than 70 % of recruitment variability explained (R = 0.852, F1,10 0.303, F1,54 = 5.477, P = 0.023). In contrast to freshwater flow, there was a strong, positive = 26.546, P < 0.001; Figure 27). When the relationship between stratification at the upper comparison with freshwater flow was extended back to 1993 using all available recruitment data, site and recruitment (R = 0.726, F1,16 = 17.879, P = 0.001; Figure 24). there was no significant relationship between freshwater flow and recruitment. There was a In the Surry estuary there were no significant strong, positive relationship between correlations between freshwater flow and recruitment and stratification at both the stratification between 2004 and 2010. There was entrance and mid sites, with the highest also no significant relationship between variance in recruitment explained (80%) by freshwater flow and recruitment over this stratification averaged across sites (R = 0.893, period. When the comparison was extended F1,10 = 39.253, P < 0.001; Figure 28). back to 1994 using all available recruitment data, there was a significant negative correlation In the Hopkins estuary there was a positive between freshwater flow and recruitment (R = relationship between freshwater flow and stratification between 2004 and 2010; however, 0.568, F1,15 = 7.127, P = 0.017; Figure 25). There was a positive relationship between this was not statistically significant. There was stratification and recruitment at the upper site; also no significant relationship between however, this was not statistically significant, freshwater flow and recruitment over this most likely due to the small sample size (n = 6, R period. When the comparison was extended = 0.565, P = 0.242). A multiple regression of back to 1990 using all available recruitment data, recruitment against freshwater flow and there was a significant negative correlation stratification at the upper site explained 80% of between freshwater flow and recruitment (R = ‐ recruitment variation, but was not statistically 0.289, F1,93 = 8.458, P = 0.005; Figure 29). There significant, again possibly due to the small was no significant relationship between recruitment and stratification at the individual sample size (R = 0.885, F2,3 = 5.447, P = 0.100). This suggested that good recruitment years in sites or averaged across the sites. the Surry estuary may occur under conditions of In the Snowy estuary there was a negative low freshwater flow and high stratification at correlation between black bream recruitment the upper site. and flow; however, this was not statistically In the Fitzroy estuary there were no significant significant (n = 13, R = ‐0.461, P = 0.113). correlations between freshwater flow and Estuary perch stratification between 2004 and 2010. There was As mentioned, in the Glenelg estuary there was also no significant relationship between a strong negative relationship between freshwater flow and recruitment over this freshwater flow and the level of stratification at period. When the comparison was extended the upper site between 2004 and 2010. Over the back to 1996 using all available recruitment data, same period there was a positive relationship there was a negative correlation between between freshwater flow and recruitment of freshwater flow and recruitment; however, it

Biophysical Assessment of Black Bream and Estuary Perch 27 estuary perch; however, this was non‐significant There was a significant positive relationship (n = 11, R = 0.574, P = 0.065). When the between recruitment and stratification at the comparison with freshwater flow was extended lower and mid sites, as well as stratification back to 2002 using all available recruitment data, averaged over sites. The highest amount of there was a positive relationship between recruitment variability (36%) was explained by freshwater flow and recruitment, but this was stratification at the lower site (R = 0.603, F1,15 = also non‐significant (n = 17, R = 0.420, P = 0.093). 6.186, P = 0.010; Figure 32). There was an There was a strong and significant negative improvement in the amount of recruitment relationship between recruitment and variability explained (52%) when stratification stratification at the mid and upper sites, as well averaged across sites and freshwater flow were as stratification averaged over sites (R = 0.821, included as independent variables in a multiple F1,9 = 16.386, P = 0.002; Figure 30) which regression (R = 0.721, F2,154= 4.424, P = 0.006). This explained nearly 70% of the recruitment result indicated that high estuary perch variability. The variance in recruitment recruitment in the Hopkins estuary occurred in explained improved to over 75% when years of increased freshwater flow and reduced stratification averaged over sites and freshwater stratification. flow were included in a multiple regression (R = In the Snowy estuary there was a positive 0.874, F2,8 = 12.980, P = 0.003). This result correlation between estuary perch recruitment indicated that high estuary perch recruitment in and flow, however this was not statistically the Glenelg estuary occurred in years of significant (n = 9, R = 0.428, P = 0.250). increased freshwater flow and reduced stratification. In the Hopkins estuary, as already mentioned, there was a positive but non‐significant relationship between freshwater flow and stratification between 2004 and 2010. Over the same period there was a significant positive relationship between recruitment and freshwater flow (R = 0.606, F1,21 = 12.162, P = 0.002; Figure 31). When the comparison was extended back to flow and stratification at the 1990 using all available recruitment data, there was no significant correlation with freshwater flow.

Biophysical Assessment of Black Bream and Estuary Perch 28

-1 Catch curve residuals Catch curve

-2

-3 0 500 1000 1500 2000

Freshwater flow (ML/d) Figure 23. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (2004 – 2010) in the Glenelg estuary

-1 Catch curve residuals curve Catch

-2

-3 15 20 25 30 35

Stratification index Figure 24. The relationship between recruitment of black bream estimated by catch curve residuals and stratification (1995 – 2010) at the upper site in the Glenelg estuary

Biophysical Assessment of Black Bream and Estuary Perch 29 3

-1 Catchresiduals curve

-2

-3 0 100 200 300

Freshwater flow (ML/d) Figure 25. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (1994 – 2010) in the Surry estuary

-1 Catchresiduals curve

-2

-3 0 5 10 15

Stratification index Figure 26. The relationship between recruitment of black bream estimated by catch curve residuals and stratification (1996 – 2010) averaged over sites in the Fitzroy estuary

Biophysical Assessment of Black Bream and Estuary Perch 30

-1 Catch curve residuals curve Catch

-2

-3 0 50 100 150 200 250

Freshwater flow (ML/d) Figure 27. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (2004 – 2010) in the Eumeralla estuary

-1 Catch curve residuals Catch curve

-2

-3 0 5 10 15

Stratification index

Figure 28. The relationship between recruitment of black bream estimated by catch curve residuals and stratification (1993 – 2010) averaged over sites in the Eumeralla estuary

Biophysical Assessment of Black Bream and Estuary Perch 31

Catch curve residuals -1

-2

-3 0 1000 2000 3000 4000

Freshwater flow (ML/d) Figure 29. The relationship between recruitment of black bream estimated by catch curve residuals and freshwater flow (1990 – 2010) in the Hopkins estuary

Catch curve residuals Catch curve -1

-2

-3 20 22 24 26 28 30

Stratification index Figure 30. The relationship between recruitment of estuary perch estimated by catch curve residuals and stratification (2002 – 2010) averaged over sites in the Glenelg estuary

Biophysical Assessment of Black Bream and Estuary Perch 32

-1 Catch curve residuals curve Catch

-2

-3 0 100 200 300 400 500 600 700 800 900

Freshwater flow (ML/d) Figure 31. The relationship between recruitment of estuary perch estimated by catch curve residuals and freshwater flow (2004 – 2010) in the Hopkins estuary

-1 Catch curve residuals

-2

-3 5 10152025

Stratification index Figure 32. The relationship between recruitment of estuary perch estimated by catch curve residuals and stratification (1990 – 2010) at the lower site in the Hopkins estuary

Biophysical Assessment of Black Bream and Estuary Perch 33 Discussion

Physical characteristics Recruitment of black bream and Freshwater flows into the estuaries considered in estuary perch this study were similar over a thirty year period, Both black bream and estuary perch showed reflecting long‐term climate phenomena such as highly variable recruitment in this study. This is the decade long drought that extended from the consistent with previous studies on black bream late 1990s to the late 2000s, and shorter term, 2 – in Gippsland Lakes (Morison et al. 1998; Jenkins 5 year variation in the El Nino Southern et al. 2010), and estuary perch in the Bemm River Oscillation (ENSO), such as the intense El Nino (Walsh et al. 2010). This ‘episodic’ recruitment in 1998 – 1999 where conditions were very dry, to suggests that suitable conditions for spawning the intense La Nina of 2009 – 2011 when major and egg – larval – juvenile survival occurs on an flooding occurred across Victoria. infrequent basis reflecting variability in the Considering that the inflows to estuaries were estuarine environment. relatively similar, there was considerable The influence of broad‐scale climatic factors such variation in the characteristics of salinity as rainfall on recruitment variability in these stratification amongst the estuaries over the July species was suggested by the similarity in to December period. In the Glenelg estuary, recruitment patterns for black bream in the three increasing flows led to reduced stratification at most western Victorian estuaries, and the the upper site, while in the Eumeralla estuary, similarity in recruitment of estuary perch increased flows led to increased stratification between the Snowy and Glenelg estuaries. On averaged across sites. These differences reflect the other hand, local‐scale influences were the interaction of inflows with the topography suggested by the fact that other estuaries show and bathymetry of the estuary, and also the unique recruitment patterns, an example being estuary mouth opening characteristics. the Hopkins estuary for both species. The results The estuaries considered in this study varied clearly showed that recruitment patterns for greatly in their topography and bathymetry, black bream and estuary perch are substantially ranging from a relatively linear, larger and different across the estuaries studied, suggesting longer estuary such as the Glenelg, to linear the environmental requirements of the two estuaries that were smaller, shorter and species for successful recruitment are also shallower such as the Surry and the Fitzroy. The substantially different. Eumeralla and Snowy estuaries had broader In Victoria, spring is considered to be the lagoon and fringing wetland systems near the primary spawning period for both black bream mouth, while the Hopkins estuary was (Newton 1996; Nicholson et al. 2008; Jenkins et al. characterised by deep pools. 2010) and estuary perch (Walsh et al. 2010; Walsh The western Victorian estuaries considered in et al. 2011). The spawning habitat of the two this study were intermittently open while the species, however, may be quite different. Black Snowy estuary is permanently open (Barton et al. bream egg and larval distribution and survival is 2008). Estuaries in western Victoria are generally greatest at intermediate salinities (10‐20) characterised by a seasonal hydrological cycle (Newton 1996; Haddy and Pankhurst 1998; 2000; (Newton 1996). Low flows in summer – autumn Nicholson et al. 2008) and often (Nicholson et al. lead to high stratification and depleted oxygen 2008; Williams et al. 2012) but not always (Sakabe near the bottom (Newton 1996). Higher flows in and Lyle 2010; Sakabe et al. 2011) in association winter – spring lead to reduced stratification and with strong salinity stratification (salt wedge increased dissolved oxygen, with a gradual re‐ development). These environmental conditions development of stratification in early summer mean that under low flow conditions spawning (Newton 1996). Entrance closure is most likely to may occur well upstream in the estuary (Sakabe occur under low flow conditions and opening is et al. 2011). Although less is known about the likely when strong flows occur. The pattern of spawning locations of estuary perch, it is entrance opening and closing is irregular and is generally thought that this species moves often managed artificially. downstream and spawns in higher salinity water

Biophysical Assessment of Black Bream and Estuary Perch 34 near the mouths of estuaries (Douglas 2010; The mechanism for increased recruitment of Walsh et al. 2011). These potential differences in estuary perch in years of increased freshwater spawning habitat suggest different flow and reduced stratification is unknown, environmental requirements for successful mainly because of our poor knowledge of the recruitment. biology of this species. Trnski et al. (2005) collected estuary perch larvae entering a central Effects of freshwater flow and New South Wales estuary from the ocean on a flood tide, suggesting that larvae were stratification on recruitment potentially dispersed into the sea after spawning. In the case of black bream there was a general This dispersal from spawning areas near the trend across the estuaries for recruitment to be mouths of estuaries would be enhanced under higher in years of reduced flows. The only conditions of high freshwater flow (and high exceptions were for the Eumeralla estuary and flow may be required to open the estuary mouth for recent drought years in the Hopkins estuary in some systems). Another possible advantage of where there was a positive relationship with flow spawning under higher flow conditions would in contrast to a negative relationship over the be that areas of low dissolved oxygen formed longer term. In contrast to freshwater flow, under low flow and highly stratified conditions recruitment of black bream was generally higher would be flushed from the system. in years of high stratification, with 80 – 90 % of recruitment variability in the Fitzroy and Re‐assessment of results from Eumeralla estuaries explained by stratification alone. Gippland lakes In undertaking ageing for the present study, we In general, there was a consistent trend across realised that the standard ageing technique estuaries for recruitment of black bream to be previously used for black bream did not take into higher in years of lower freshwater flow and account the spring spawning period. The increased stratification. It is difficult to determine notional year class of 0+ fish using the standard which of these variables is of greater importance ageing method actually represented the year because they tend to be related in these systems, after the spawning year. This meant that it was with low flows leading to higher stratification necessary to lag our recruitment estimates by one (Newton 1996). Stratified conditions in the salt year when comparing with flow and wedge have been found to be areas of high stratification data. In our earlier study of black productivity of zooplankton prey for fish larvae bream recruitment in Gippsland Lakes, pre‐ (Sirois and Dodson 2000; North and Houde 2001; existing ageing data was used that was not 2003; Shoji et al. 2005), thereby possibly adjusted for the spring spawning period (Jenkins enhancing the survival of larval bream. Recent 2010). Like the present study, a strong positive sampling of the Mitchell River has shown high correlation was found between recruitment and concentrations of zooplankton prey associated stratification in Gippsland Lakes; however, this with the highly stratified area of the salt wedge correlation related to 0+ juveniles of 6 – 12 in areas of highest black bream abundance (J. months age rather than eggs and larvae as was Williams, unpublished manuscript). In contrast, assumed at the time (Jenkins 2010). Multiple black bream in the Swan estuary, Tasmania, were regression analysis suggested that highest found to spawn upstream in low flow conditions recruitment of 0+ juveniles occurred in conditions in the absence of strong water column of high stratification in the Lakes and stratification (Sakabe and Lyle 2010; Sakabe et al. intermediate freshwater flows in the rivers, 2011). contrasting with high recruitment in low river In contrast to black bream, recruitment of estuary flow conditions found in the present study. The perch tended to be higher in years of increased high stratification in the lakes from June to freshwater flow. Also in contrast to black bream, December could be indicative of high freshwater recruitment of estuary perch was reduced in the flows earlier in the year. Indeed, further analysis Glenelg estuary in years of high stratification. has shown a positive relationship between flow Although there was a positive relationship from January to June in the year after spawning between estuary perch recruitment and and year class strength (R = 0.581, F1,63 = 32.132, P stratification in the Hopkins, there was a stronger < 0.001). The regression indicated that a relationship in a multiple regression showing combined average flow from the Mitchell, Tambo higher recruitment in years of increased and Nicholson Rivers of approximately 2500 freshwater flow and reduced stratification. ML/d from the January to June period resulted in

Biophysical Assessment of Black Bream and Estuary Perch 35 higher recruitment. This correlation between 23.786, P < 0.001), suggesting recruitment was flows and abundance of 0+ juveniles is supported stronger when flows were reduced over the by a previous analysis that showed a positive spawning period; this is consistent with the correlation between rainfall in the May after results for black bream across estuaries in the spawning and year class strength of black bream present study. This result was also consistent in Gippsland Lakes (Walker et al. 1998). with previous analyses of black bream recruitment in the Gippsland Lakes showing that This re‐assessment means that the originally dominant year classes were associated with low proposed hypothesis of high egg and larval river flow in October during the spawning survival when the Gippsland Lakes are stratified, period (Hobday and Moran 1983; Walker et al. because suitable spawning and larval survival 1998). conditions expanded beyond the feeder rivers (Jenkins 2010) must be reassessed. A possible These results suggest a possible two‐phase mechanism that could explain higher recruitment mechanism leading to high recruitment in the of 0+ juveniles under intermediate flows and Gippsland Lakes, where successful spawning stratified conditions in the lakes is that significant and larval survival occurs in the salt wedge in freshwater flows after the spawning period may feeder rivers under relatively low flow increase the available habitat for juveniles in their conditions (Williams et al. 2012), but is then first year of life by allowing them to spread from followed by higher freshwater flow after the rivers into the lakes where extensive seagrass spawning period that would create a suitable beds occur. Higher flows could also improve the habitat for juveniles in the lakes. A caveat is that suitability of habitat areas for juvenile bream in the analysis in Gippsland Lakes occurred over a the lakes by increasing dissolved oxygen levels relatively high flow period (1986–1990), and it is that can be chronically low under reduced flow possible that under very low flow conditions as conditions (Walker et al. 1998). occurred in the recent drought, conditions for spawning and egg and larval survival could be When the recruitment estimated from age affected where salt water intrusion reaches structure in Gippsland Lakes was re‐analysed barriers in the river (for example the weir in the with a one year lag in the recruitment estimates Mitchell River) and the salt wedge is reduced. (Jenkins 2010), a negative relationship with freshwater flow was found (R = 0.369, F1,58 = 9.162, P < 0.004) together with a positive relationship with surface salinity in the Lakes (R = 0.557, F1,53 =

Biophysical Assessment of Black Bream and Estuary Perch 36 Conclusions

period will become more intermittent and intense Potential climate change (Anon. 2007). Although rainfall will not change implications for two important markedly over summer autumn, increased Victorian estuarine fish species evaporation may still lead to a decline in freshwater flows over this period. A key result from this study is that two important estuarine fish species with high levels Based on the results of this study, these changes of recruitment variability and similar spawning may be largely favourable for black bream but periods have almost opposite requirements in negative for estuary perch populations in terms of freshwater flow and stratification for Victoria. Black bream will be favoured in most successful recruitment. Strong year classes of systems by lower flows over the spawning black bream tend to be associated with lower period leading to salt wedge development and river flow and higher salinity stratification over stratification. In the Gippsland Lakes, the fact the spawning period while for estuary perch the that flows will not greatly decline in the autumn opposite is true, with higher flow years and period should limit the negative effect of climate lower stratification resulting in stronger year change, although the impact of flow events classes. For black bream the situation may be becoming more intermittent and intense over this more complicated in the Gippsland Lakes, with period is unknown. In contrast, our results strong year classes apparently resulting from a suggest that lower flows over the spring two phase mechanism where low freshwater spawning period of estuary perch will have a flow occurs over the spawning season and then is deleterious effect on the populations in most followed by higher flows after the spawning systems. season during the first year of juvenile life. As a result of this divergence in environmental Opportunities for improving the requirements it is clear that significant inter‐ resilience and adaptation of black annual variability in the flow regime is required bream and estuary perch to to support both species. This inter‐annual variability is driven by the ENSO cycle at the climate change scale of a few years and also by longer term The key to resilience of these species under climate variation such as extended droughts and climate change will be for managers, in particular wet periods. These two species are well adapted catchment mangers, to maintain flows and flow to this variability through their longevity (over variability at similar levels to that which has 30 years) and ability to produce strong year occurred historically. The results of this study classes on an episodic basis when conditions are show that there in no single flow level or narrow suitable. Because strong year classes of the two range of flow levels that can be set to maintain species will tend to occur in different years there resilience of fish species in the system. The is less potential for competition for resources resilience of these two species relies on the between the two species in the early life stages. maintenance of inter‐annual variability in flows so that suitable conditions of recruitment of both Climate change is likely to result in both a species will occur frequently enough for seasonal shift and a regime shift in the amount of populations to be supported. Under climate freshwater flow entering Victorian estuaries. The change there will be an overall reduction in flows regime shift in freshwater flows will see runoff in the spring, and in the case of estuary perch, it reduced by in the order of 30% by 2060 (Mills may be critical to ensure that significant flows and Womersley 2012) through the effects of occur over the spring period in some years. Even reduced rainfall and increased solar radiation in the case of black bream, although low spring and decreased humidity leading to increased flows are beneficial in maintaining the stratified evaporation rates (Anon. 2007). The seasonal salt wedge in the system, if flows become too low shift will see a marked reduction in the rainfall then conditions may deteriorate where there are and associated flows over the spring period but stream barriers. Examples would be in the little reduction in rainfall over the summer to Mitchell River where there is an artificial barrier autumn period, although rainfall events over this or the Hopkins where there is a natural barrier,

Biophysical Assessment of Black Bream and Estuary Perch 37 where under very low flows essentially marine estuary perch, possible dispersal of larvae to the conditions would occur up to the barrier and sea. This is an area that requires more focus in bream spawning would be severely terms of estuary management and climate compromised. change impacts. In this respect, proposals to open up the Gippsland Lakes to more exchange with In some systems there may be exceptions to these the sea will need to be considered in light of general principles of environmental requirements potential negative impacts on bream recruitment for successful spawning of these species. For where stratified conditions in the lakes may be example, black bream recruitment in the necessary over the first year of life for successful Eumeralla estuary was positively related to recruitment. Opening the lakes to the sea would freshwater flow, so in this system reduced spring tend to make them a marine dominated system flows under climate change may have a negative with low stratification. effect on bream recruitment. This indicates that although general principles apply, management It is well known that climate change is likely to in some cases may need to be tailored to result in winners and losers and it appears from individual estuarine systems. In the case of black this study that black bream in Victoria may bream, it appears to be the presence of generally be “winners” and estuary perch may be stratification, whether maintained by low or high “losers”. Management will need to focus on flow depending on the system, which is critical. maintaining natural variability in flows to which these species are adapted. In terms of fisheries In the case of bream in the Gippsland Lakes, management, overfishing will tend to decrease catchment management will have to take into the resilience of fish populations to climate account that successful recruitment of bream change, and the sustainable management of may require a two‐phase mechanism where fishing may be most critical for the estuary perch periodically a relatively low flow over the spring fishery. spawning period is followed by a higher flow over the following twelve months. Apart from maintaining minimum flows and retaining natural variability in the flow regime as much as possible, there are other possible management actions related to estuary entrance opening and closing. Although not covered in this report due to lack of data, estuary opening and closing will be a critical factor in the development of stratification, and in the case of

Biophysical Assessment of Black Bream and Estuary Perch 38 Acknowledgements

We thank the Glenelg Hopkins Catchment Management Authority for providing physico‐ chemical data for the west Victorian estuaries.

We thank Simon Conron for the use of ageing data derived from angler diary and research angler sampling.

We wish to acknowledge the funding for this work provided by the Future Farming Strategy Initiative on climate change adaptation.

Biophysical Assessment of Black Bream and Estuary Perch 39 References

Anon. (2007). Climate change in Australia. Assessment of Key Species. Fisheries CSIRO and Australian Bureau of Victoria, Research Report Series No. 49. Meterorology, Jenkins, G. P., Conron, S. D., and Morison, A. K. http://www.climatechangeinaustralia.go (2010). Highly variable recruitment in an v.au/. estuarine fish is determined by salinity Barton, J. L., Pope, A. J., Quinn, G. P., and stratification and freshwater flow: Sherwood, J. E. (2008). Identifying implications of a changing climate. threats to the ecological condition of Marine Ecology Progress Series 417, 249‐ Victorian estuaries. Department of 261. Sustainability and Environment Maceina, M. J. (1997). Simple application of Technical Report. using residuals from catch‐curve Douglas, J. (2010). Estuary perch movement and regressions to assess year‐class strength habitat use in the Snowy River. in fish. Fisheries Research 32, 115‐121. Recreational Fishing Grant Program ‐ Mills, R., and Womersley, T. (2012). Implications Research report, Fisheries Victoria. of future climate for Victoriaʹs Marine Haddy, J. A., and Pankhurst, N. W. (1998). Environment: Physicochemical Annual change in reproductive conditions. Water Technology Report condition and plasma concentrations of for Glenelg Hopkins Catchment sex steroids in black bream, Management Authority (Draft). Acanthopagrus butcheri (Munro) Morison, A. K., Coutin, P. C., and Robertson, S. (Sparidae). Marine and Freshwater G. (1998). Age determination of black Research 49, 389‐397. bream, Acanthopagrus butcheri Haddy, J. A., and Pankhurst, N. W. (2000). The (Sparidae), from the Gippsland Lakes of effects of salinity on reproductive south‐eastern Australia indicates slow development, plasma steroid levels, growth and episodic recruitment. fertilisation and egg survival in black Marine and Freshwater Research 49, 491‐ bream Acanthopagrus butcheri. 498. Aquaculture 188, 115‐131. Newton, G. M. (1996). Estuarine Halliday, I. A., Robins, J. B., Mayer, D. G., ichthyoplankton ecology in relation to Staunton‐Smith, J., and Sellin, M. J. hydrology and zooplankton dynamics (2008). Effects of freshwater flow on the in a salt‐wedge estuary. Marine and year‐class strength of a non‐diadromous Freshwater Research 47, 99‐111. estuarine finfish, king threadfin Nicholson, G., Jenkins, G. P., Sherwood, J., and (Polydactylus macrochir), in a dry‐tropical Longmore, A. (2008). Physical estuary. Marine and Freshwater Research environmental conditions, spawning 59, 157‐164. and early‐life stages of an estuarine fish: Hobday, D., and Moran, M. (1983). Age, growth climate change implications for and fluctuating year‐class strength in recruitment in intermittently open black bream in the Gippsland Lakes, estuaries. Marine and Freshwater Research Victoria. Marine Science Laboratories, 59, 735‐749. Ministry for Conservation, Victoria, 20. North, E. W., and Houde, E. D. (2001). Retention Hutchinson, N., Gavine, F., Morris, E., and of white perch and striped bass larvae: Longmore, A. (2010). Adaptation of Biological‐physical interactions in Fisheries and Fisheries Management to Chesapeake Bay estuarine turbidity Climate Change: Marine, estuarine and maximum. Estuaries 24, 756‐769. freshwater biophysical risk assessment. North, E. W., and Houde, E. D. (2003). Linking Department of Primary Industries, 92, ETM physics, zooplankton prey, and Queenscliff. fish early‐life histories to striped bass Jenkins, G. P. (2010). Fisheries Adaptation to Morone saxatilis and white perch M. Climate Change – Marine Biophysical

Biophysical Assessment of Black Bream and Estuary Perch 40 americana recruitment. Marine Ecology (Macquaria colonorum) and Australian Progress Series 260, 219‐236. bass (M‐novemaculeata) (Perciformes : Poloczanska, E. S., Babcock, R. C., Butler, A., Percichthyidae), and comments on their Hobday, A. J., Hoegh‐Guldberg, O., life history. Fishery Bulletin 103, 183‐194. Kunz, T. J., Matear, R., Milton, D. A., Walker, S., Sporcic, M., and Coutin, P. (1998). Okey, T. A., and Richardson, A. J. Development of an environment‐ (2007). Climate change and Australian recruitment model for black bream: a marine life. In ʹOceanography and case study for estuarine fisheries Marine Biologyʹ. (Eds R. N. Gibson, J. D. management. Fisheries Research and M. Gordon and R. J. A. Atkinson.) pp. Development Corporation, 96/102, 407‐478. (Taylor & Francis: Boca Raton.) Canberra. Quinn, G. P., and Keough, M. J. (2002). Walsh, C. T., Gray, C. A., West, R. J., D.E., v. d. ʹExperimental Design and Data Analysis M., and L.F.G., W. (2010). Growth, for Biologists.ʹ (Cambridge University episodic recruitment and age truncation Press: Cambridge.) in populations of a catadromous Sakabe, R., and Lyle, J. M. (2010). The influence percichthyid, Macquaria colonorum. of tidal cycles and freshwater inflow on Marine and Freshwater Research 61, 397– the distribution and movement of an 407. estuarine resident fish Acanthopagrus Walsh, C. T., Gray, C. A., West, R. J., and L.F.G., butcheri. Journal of Fish Biology 77, 643‐ W. (2011). Reproductive biology and 660. spawning strategy of the catadromous Sakabe, R., Lyle, J. M., and Crawford, C. M. percichthyid, Macquaria colonorum (2011). The influence of freshwater (Günther, 1863). Environmental Biology of inflows on spawning success and early Fishes 91, 471–486. growth of an estuarine resident fish Williams, J., Hindell, J. S., Swearer, S. E., and species, Acanthopagrus butcheri. Journal of Jenkins, G. P. (2012). Influence of Fish Biology 78, 1529‐1544. freshwater flows on the distribution of Sherwood, J., Mondon, J., and Fenton, C. (2008). eggs and larvae of black bream Classification and management issues of Acanthopagrus butcheri within a drought‐ estuaries in Western Victoria, Australia. affected estuary. Journal of Fish Biology Proceedings of the Royal Society of Victoria 80, 2281‐2301. 120, 257‐276. Shoji, J., North, E. W., and Houde, E. D. (2005). The feeding ecology of Morone americana larvae in the Chesapeake Bay estuarine turbidity maximum: the influence of physical conditions and prey concentrations. Journal of Fish Biology 66, 1328‐1341. Sirois, P., and Dodson, J. J. (2000). Influence of turbidity, food density and parasites on the ingestion and growth of larval rainbow smelt Osmerus mordax in an estuarine turbidity maximum. Marine Ecology Progress Series 193, 167‐179. Staunton‐Smith, J., Robins, J. B., Mayer, D. G., Sellin, M. J., and Halliday, I. A. (2004). Does the quantity and timing of fresh water flowing into a dry tropical estuary affect year‐class strength of barramundi (Lates calcarifer)? Marine & Freshwater Research 55, 787‐797. Trnski, T., Hay, A. C., and Fielder, D. S. (2005). Larval development of estuary perch

Biophysical Assessment of Black Bream and Estuary Perch 41