TEST OF SALT MARSH AS A SITE OF PRODUCTION AND EXPORT OF FISH BIOMASS WITH IMPLICATIONS FOR IMPOUNDMENT MANAGEMENT AND RESTORATION
By
PHILIP W. STEVENS
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2002
ACKNOWLEDGMENTS
Dr. Clay Montague, my advisor and mentor, offered his valuable time, advice, and unique ecological perspective that made this dissertation a very enjoyable and rewarding experience. Dr. Kenneth Sulak, my co-chair and friend, gave me the encouragement, employment, and freedom to pursue this project. I also appreciate his confidence in my abilities to lead projects and author scientific papers during my residence with the US
Geological Survey. My committee members, Dr. Thomas Crisman and Dr. Franklin
Percival, provided valuable input and helpful critique. Dr. George Dennis provided knowledge of fish identification, statistical analyses, and project organization. Andy
Quaid maintained datasondes in the study area, which rendered the much needed water level data that drive the ecology of this nontidal environment. The refuge managers and staff at Merritt Island National Wildlife Refuge and Canaveral National Seashore provided access to field sites, knowledge and history of impoundment ecology, and protection from the ever-present NASA security. Florida Sea Grant and the Aylesworth
Foundation provided academic financial assistance, and the US Geological Survey
Coastal Restoration Initiative provided logistics and employment. All of my field work could not have been done alone, and the following people provided enthusiastic field assistance despite the hardships of impoundment research: Cliff Bennett, James Berg,
Nick Flavin, Mike Randall, Eric Rolla, James Russell, Pam Schofield, Mat Schreiner,
Scott Stahl, George Stevens, and George Yeargin.
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Throughout my endeavors, my parents, George and Yvonne Stevens, and my sister, Carla Stevens, have provided support and encouragement. My wife, Jackie
Stevens, has always encouraged me to pursue my goals and aspirations, and has made many sacrifices on my account. I would like to thank them for their continued support and especially their patience.
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TABLE OF CONTENTS
ACKNOWLEDGMENTS ...... ii
LIST OF TABLES ...... vii
LIST OF FIGURES...... x
ABSTRACT...... xiv
CHAPTER
1 INTRODUCTION...... 1
The Role of Nekton in Saltmarsh/Estuarine Interactions...... 2 Production and Export of Nekton from Salt Marshes...... 5 Saltmarsh Impoundments in East-Central Florida...... 6 Hydrology of Saltmarsh Impoundments in East-Central Florida...... 9 Consumption and Migration of Fish Biomass from the Saltmarsh...... 10 Management and Restoration of Impoundments ...... 11 Hypotheses – Resident Migrations ...... 12 Hypotheses – Trophic Relay by Transients...... 13
2 FIELD METHODS ...... 23
Study Area...... 24 Water Conditions ...... 26 Fish Standing Stock ...... 27 Fish Ingress/Egress...... 30 Piscivores ...... 32 Statistical Analysis...... 33
3 FIELD RESULTS ...... 43
Water Conditions ...... 43 Pattern of Fish Use and Piscivore Abundance within the Impoundment...... 44 Fish Standing Stock ...... 46 Impoundment Marsh Surface...... 46 Impoundment Ditch, Creek, and Estuary Shoreline...... 46 Size Distribution of Fishes within the Impoundment ...... 48
iv
Fish Ingress/Egress...... 48 Piscivorous Fishes...... 50 Piscivorous Birds ...... 52 Notable Observations...... 52
4 FIELD DISCUSSION...... 108
Water Conditions ...... 108 Resident Fish Hypotheses ...... 109 Juvenile Transient Fish Hypotheses...... 112 Large Piscivorous Fish Hypotheses ...... 113 Other Piscivorous Animals ...... 114 Fish Use of Marsh Habitats...... 114 Conclusions...... 116
5 BIOMASS BUDGET DERIVATION ...... 118
Production Estimate from Ricker Equations...... 118 Production Estimate from Biomass Budget...... 119 Estimates of Biomass Budget Parameters...... 119 Sensitivity Analysis of Biomass Budget ...... 122
6 BIOMASS BUDGET RESULTS ...... 131
7 BIOMASS BUDGET DISCUSSION ...... 137
8 OVERALL DISCUSSION...... 145
Impoundment Management Strategies...... 145 Implications of Impoundment Management Strategies ...... 147 Conflicts between Bird and Fish Management ...... 149 Impoundment Restoration Strategies...... 150 Implications of Impoundment Restoration Strategies...... 151 Conclusions...... 154
APPENDIX
A LENGTH-WEIGHT RELATIONSHIPS FOR FISHES ...... 160
B CORRELATIONS AMONG FISH CATCHES AND WATER CONDITIONS ..... 163
C ESTIMATED BIOMASS OF FISH CAPTURED DURING STUDY ...... 175
LIST OF REFERENCES ...... 186
v
BIOGRAPHICAL SKETCH ...... 195
vi
LIST OF TABLES
Table page
1. Species cited in study...... 35
2. Terms used to describe various places, habitats, and species ...... 37
3. Summary of monthly gear deployments ...... 38
4. Fish captured by cast net on the marsh surface...... 55
5. Fish density on the marsh surface ...... 56
6. Fish captured by cast net within ditch and creek in Impoundment C20C...... 57
7. Fish captured by cast net along Banana Creek shoreline...... 58
8. Comparison of fish density among saltmarsh habitats and estuary shoreline...... 59
9. Comparison of fish catch between reduced flow and unmodified culvert traps...... 60
10. Number of small fish moving out of Impoundment C20C captured by culvert trap ...... 61
11. Number of small fish moving into Impoundment C20C captured by culvert trap ...... 63
12. Net egress of resident fish from Impoundment C20C over the study period...... 65
13. Comparison of net fish ingress among culvert locations ...... 66
14. Number of large fish moving in and out of Impoundment C20C captured by culvert trap ...... 67
15. Fish captured by gill net within Impoundment C20C...... 68
16. Fish captured by gill net along Banana Creek shoreline...... 69
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17. Comparison of piscivorous and nonpiscivorous fish catch among saltmarsh habitats and estuary shoreline ...... 70
18. Stomach contents of piscivorous fish caught in gill nets...... 71
19. Birds present within Impoundment C20C during monthly counts ...... 72
20. Birds present along Banana Creek shoreline during monthly counts ...... 73
21. Comparison of bird abundance among saltmarsh habitats and estuary shoreline... 74
22. Estimates of monthly fish standing stock within Impoundment C20C ...... 123
23. Estimates of monthly net fish ingress into Impoundment C20C ...... 124
24. Estimates of Florida gar abundance within the impoundment...... 125
25. Conversion from catch per unit effort to impoundment gar population ...... 125
26. Daily prey consumption per predator body weight for selected estuarine fishes.... 126
27. Estimates of monthly fish consumption by piscivorous fishes within Impoundment C20C...... 127
28. Daily fish consumption by piscivorous birds...... 128
29. Estimates of monthly fish consumption by birds within Impoundment C20C...... 129
30. Fish production within Impoundment C20C estimated from Ricker equations...... 133
31. Fish production within Impoundment C20C estimated from fish biomass budget...... 134
32. Sensitivity analysis of impoundment fish biomass budget ...... 135
33. Estimated fish production incorporating net fish ingress from marsh surface and other disappearance...... 141
34. Estimates of fish production among estuarine communities ...... 142
35. Length-weight relationships of fishes collected within Merritt Island NWR ...... 161
36. Monthly water conditions and culvert water flow in Impoundment C20C during the study period ...... 164
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37. Pearson’s correlation among average monthly animal catches and average monthly water conditions...... 165
38. Spearman’s correlation among average monthly animal catches and average monthly water conditions...... 170
39. Biomass of fish captured by cast net on the marsh surface...... 176
40. Biomass of fish captured by cast net within ditch and creek in Impoundment C20C...... 177
41. Biomass of fish captured by cast net along Banana Creek shoreline...... 178
42. Biomass of small fish moving out of Impoundment C20C captured by culvert trap ...... 179
43. Biomass of small fish moving into Impoundment C20C captured by culvert trap ...... 181
44. Biomass of large fish moving in and out of Impoundment C20C captured by culvert trap ...... 183
45. Biomass of fish captured by gill net within Impoundment C20C...... 184
46. Biomass of fish captured by gill net along Banana Creek shoreline...... 185
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LIST OF FIGURES
Figure page
1. Energy flow diagram illustrating impoundment trophic interactions within a saltmarsh impoundment and exchanges with the adjacent estuary...... 16
2. Nekton biomass budget in a saltmarsh impoundment ...... 17
3. Illustration of Resident Hypothesis 1...... 18
4. Illustration of Resident Hypothesis 2...... 19
5. Illustration of Juvenile Transient Hypothesis 1 ...... 20
6. Illustration of Juvenile Transient Hypothesis 2 ...... 21
7. Illustration of Juvenile Transient Hypothesis 3 ...... 22
8. Location of study site (Banana Creek) within the northern Indian River Lagoon system ...... 39
9. Map of Impoundment C20C within Kennedy Space Center ...... 40
10. Map of Impoundment C20C showing vegetation types, culvert locations, and datasonde locations ...... 41
11. Gill net deployment locations within Impoundment C20C ...... 42
12. Water level during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek ...... 75
13. Water temperature during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek ...... 76
14. Diurnal changes in temperature during a typical 10-day period ...... 77
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15. Salinty during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek ...... 78
16. Dissolved oxygen during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek ...... 79
17. Redox potential during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek ...... 80
18. Diurnal changes in dissolved oxygen during a typical 10-day period...... 81
19. Diurnal changes in redox potential during a typical 10-day period ...... 82
20. pH during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek ...... 83
21. Diurnal changes in pH during a typical 10-day period ...... 84
22. Average monthly water flow through Impoundment C20C culverts during study period...... 85
23. Average water level, and numbers involved in net fish migration, fish standing stock, piscivorous fish catch per unit effort, and piscivorous bird abundance...... 86
24. Average water level, and biomass involved in net fish migration, fish standing stock, piscivorous fish catch per unit effort, and piscivorous bird abundance...... 87
25. Number and biomass of the standing stock of resident fishes by habitat ...... 88
26. Number and biomass of the standing stock of transient fishes by habitat ...... 89
27. Size frequency of Cyprinodon variegatus caught by cast net on the marsh surface at Impoundment C20C...... 90
28. Size frequency of Poecilia latipinna caught by cast net on the marsh surface at Impoundment C20C...... 91
29. Size frequency of Poecilia latipinna caught by cast net in ditch and creek within Impoundment C20C...... 92
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30. Size frequency of Gambusia holbrooki caught by cast net in ditch and creek within Impoundment C20C...... 93
31. Size frequency of Cyprinodon variegatus caught by cast net in ditch creek within Impoundment C20C...... 94
32. Size frequency of Menidia peninsulae caught by cast net in ditch and creek within Impoundment C20C...... 95
33. Size frequency of Mugil cephalus caught by cast net in ditch and creek within Impoundment C20C...... 96
34. Size frequency of Lucania parva caught by cast net in ditch and creek within Impoundment C20C...... 97
35. Catch rate of resident fish in culvert traps during study period ...... 98
36. Net resident fish ingress by culvert location...... 99
37. Catch rate of transient fish in culvert traps during study period ...... 100
38. Net transient fish ingress by culvert location...... 101
39. Piscivorous fish catch per unit effort in gill nets by habitat...... 102
40. Size frequency of Sciaenops ocellatus captured by culvert trap and gill net during study period in Impoundment C20C...... 103
41. Size frequency of Elops saurus captured by cast net, culvert trap, and gill net during study period in Impoundment C20C...... 104
42. Size frequency of Leiostomus xanthurus captured by cast net, culvert trap, and gill net during study period in Impoundment C20C...... 105
43. Size frequency of Cynoscion nebulosus captured by culvert trap and gill net during study period in Impoundment C20C...... 106
44. Number and estimated biomass of piscivorous birds by habitat...... 107
45. Derivation of fish production equation for biomass budget ...... 130
46. Estimated fish production, water level, and marsh elevation in Impoundment C20C during study period...... 143
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47. Consumption and migration of fish production from Impoundment C20C...... 144
48. Management strategies of coastal wetland impoundments in the Indian River Lagoon, Florida...... 157
49. Restoration strategies of coastal wetland impoundments in the Indian River Lagoon, Florida...... 158
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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy
TEST OF SALT MARSH AS A SITE OF PRODUCTION AND EXPORT OF FISH BIOMASS WITH IMPLICATIONS TO IMPOUNDMENT MANAGEMENT AND RESTORATION
By
Philip Stevens
August 2002
Chairman: Clay L. Montague Major Department: Environmental Engineering Sciences
Salt marshes are among the most productive ecosystems in the world, and although they are thought to enhance the productivity of open estuarine waters, the mechanism by which energy transfer occurs has been debated for decades. One possible mechanism is the transfer of saltmarsh production to estuarine waters by vagile fishes and invertebrates. Saltmarsh impoundments in the Indian River Lagoon, Florida, that have been reconnected to the estuary by culverts provide unique opportunities for studying marsh systems with respect to aquatic communities. The boundaries between salt marshes and the estuary are clearly defined by a system of dikes that confine fishes into a known area, and the exchange of aquatic organisms are restricted to culverts where they may be easily sampled. A multi-gear approach was used monthly to estimate fish standing stock, fish ingress/egress, and predation. Changes in saltmarsh fish abundance, and exchange with the estuary reflected the seasonal pattern of marsh flooding in the
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northern Indian River Lagoon system. During a six month period of marsh flooding,
saltmarsh fishes had continuous access to marsh food resources. Piscivorous fishes
regularly entered the marsh via creeks and ditches to prey upon marsh fishes, and
piscivorous birds aggregated following major fish migrations to the marsh surface or to
deep habitats. As water levels receded in winter, saltmarsh fishes concentrated into deep
habitats and migration to the estuary ensued. The monthly estimates of fish standing
stock, net fish ingress, and predation were used to develop a biomass budget to estimate
annual production of fishes and the relative yield to predatory fish, birds, and direct
migration to the estuary. Annual production of saltmarsh fishes was estimated to be 17.7
g·m-2 salt marsh, which falls within the range of previously reported values for estuarine fish communities. The relative yields were at least 21% to piscivorous fishes, 14% to piscivorous birds, and 32% to export. Annual export of fish biomass was 5.6 g fish·m-2
salt marsh, representing about 2% of saltmarsh primary production. Saltmarsh fishes
convert marsh production to high quality vagile biomass (fishes concentrate energy,
protein, and nutrients as body mass) and move this readily useable production to the
estuary, providing an efficient link between salt marshes and estuarine predators.
xv
CHAPTER 1 INTRODUCTION
Salt marshes are among the most productive ecosystems in the world (Day et al.
1989; Montague and Wiegert 1990; Mitsch and Gosselink 1993; Montague and Odum
1997), and although they are thought to enhance the productivity of open estuarine waters, the mechanism by which energy transfer occurs has been debated for decades
(Haines 1979; Nixon 1980; Dame 1994). Historically, salt marshes were thought to contribute to estuarine productivity by exporting large quantities of detritus, which then form the base of the estuarine food web (Teal 1962; Odum and de la Cruz 1967; Wiegert et al. 1975). However, detrital and dissolved organic export from salt marshes is variable among locations and is often only a minor contribution to estuarine productivity (Heinle and Flemer 1976; Marinucci 1982; Montague et al. 1987; Dame et al. 1991; Williams et al. 1992; Borey et al. 1993; Taylor and Allanson 1995). Salt marshes were also thought to supply nutrients to estuarine waters, thereby enhancing estuarine primary production
(i.e., phytoplankton production). However, the majority of nutrients contained within saltmarsh plant tissues are recycled within the marsh and little is directly exchanged with the estuary relative to demand in estuarine waters (Haines et al. 1977; Valiela and Teal
1979; Nixon 1980; Hopkinson and Schubauer 1984).
Marsh sediments and their associated microbial communities can be sources or sinks for nutrients depending on the nutrient supply from other sources such as river discharge, upland runoff, and sewage effluent (Haines et al. 1977; Valiela and Teal 1979;
1 2
Kaplan et al. 1979). For example, marshes with high input of nitrogen (the limiting nutrient in many estuaries) are likely to be sites of net denitrification, whereas marshes with low input of nitrogen are likely to be sites of net nitrogen fixation (Haines et al.
1977; Valiela and Teal 1979; Kaplan et al. 1979; Montague et al. 1987). Although the historical paradigm of salt marshes supplying detritus and nutrients directly to open estuarine waters remains equivocal, an alternative paradigm has been emerging that emphasizes the role of salt marshes in providing food and refuge to young estuarine nekton and the role of nekton in transferring saltmarsh production to estuarine waters
(Werme 1981; Haines 1979; Haines and Montague 1979; Boesch and Turner 1984;
Montague et al. 1981; Montague et al. 1987; Knieb 1997).
The Role of Nekton in Saltmarsh/Estuarine Interactions
Nekton studies in coastal wetlands recognize two components of aquatic communities: resident (those species that complete their life history within marshes), and transient (those species that use marshes periodically for food and refuge). Many transient species (e.g., drums, mullets, swimming crabs) use marshes as nurseries during early stages in their life history (Weinstein 1979; Boesch and Turner 1984; Pattillo et al.
1997). These species often arrive in saltmarsh creeks during postlarval and juvenile stages after being transported there by wind and currents directly, or by actively positioning themselves within the water column to take advantage of the movement of water masses favorable for reaching nursery areas (Weinstein et al. 1980; Pietrafesa et al.
1986). The nursery areas often include salt marshes, and also seagrasses, because these habitats offer greater food availability to many species of nekton relative to unvegetated areas (Rozas and Minello 1998), and also provide substantial refuge from predation from
3 larger estuarine species (Rozas and Odum 1988; McIvor and Odum 1988). Refuge from predation is also found in shallow water (whether vegetated or not), a common feature of saltmarsh systems (Ruiz et al. 1993; Miltner et al. 1995).
Transient juvenile nekton use salt marshes as nurseries for a few weeks to a few months (Weinstein et al. 1980; Gilmore et al. 1982). Transient juvenile species are most commonly found in tidal creeks, and although some venture onto the marsh along the edge of tidal creeks, most are never found on the interior marsh surface (Minello et al.
1994; Peterson and Turner 1994). Few transients on the marsh surface have also been reported for seasonally flooded marshes in the Indian River Lagoon system, even during periods when the marshes were continuously flooded (Klassen 1998).
Resident nekton (e.g., killifishes, livebearers) complete their entire life history within the marshes and may comprise a major portion of the forage base for larger transient nekton and avian wildlife (Kushlan 1980). The marsh surface offers a wide variety of food resources for resident nekton such as detritus, benthic microalgae, cyanobacteria, plankton, and benthic invertebrates (Harrington and Harrington 1961;
Kneib and Wagner 1994). It also provides refugia for resident fishes (e.g., killifishes, livebearers) (McIvor and Odum 1988; Knieb and Wagner 1994; Rozas 1995), although predation by birds within marshes may be quite high in some places (Kushlan 1980).
Resident fishes remain on the marsh surface during high water and retreat to pools, depressions, and creeks during low water periods to escape desiccation (Knieb and
Wagner 1994; Rozas 1995). Trophic interactions among resident and transient nekton that occur along interaction “hot-spots” (e.g., creek banks) transport marsh production across the saltmarsh landscape to the open estuary (Kneib 1997).
4
Kneib (1997) has described the movement of energy across the marsh landscape to the estuary via predator-prey relationships as “the trophic relay” and has developed a detailed conceptual model of these interactions. Resident nekton convert saltmarsh production into vagile biomass, which then may move across the marsh landscape as smaller residents are consumed by larger residents. The larger residents are more likely to move to subtidal creeks or seagrass beds during low water to escape desiccation or thermal stress on the marsh surface, which makes them susceptible to predation by young transient nekton. The latter may move to deeper estuarine waters as they mature, or may be eaten by larger adult transients that occasionally foray into marsh creeks seeking prey.
Non-predatory transient nekton, (e.g., herrings, silversides, and mullets) also incorporate marsh foods into vagile biomass when present in the marsh as juveniles.
They may be consumed by larger predatory transients during their residence within the saltmarsh, but they eventually emigrate from salt marshes to the open estuary as they reach maturity, moving the incorporated saltmarsh resources with them (Deegan 1993;
Kneib 1997).
According to Kneib (1997), the migrations involved in the “trophic relay” occur at different spatial and temporal scales. For example, daily intertidal migrations occur as resident nekton move between marsh surface and creek habitats, or transient nekton move in and out of marsh creeks. Also, seasonal migrations occur as larval and early juvenile stages move into marshes and later emigrate to the open estuary, and in some cases, the open ocean. The interspecific interactions between resident marsh fishes and transient predators that occur within the marsh may be important mechanisms for moving the marsh resources that have been incorporated into resident nekton to the adjacent estuary.
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Production and Export of Nekton from Salt Marshes
Export of fishes from salt marshes has been addressed by Deegan (1993) and
Herke et al. (1992). Deegan (1993) used wing nets to sample the migration of Brevoortia patronus from a Louisiana estuary and found that B. patronus transported substantial quantities of carbon, nitrogen, and phosphorus from the estuary to the nearshore Gulf of
Mexico. Estimated export of menhaden from the Louisiana estuary was 38 g fish·m-
2·yr-1, which represented 5 – 10% of estuarine primary production (Deegan 1993). Herke et al. (1992) used a combination of weirs and fish traps to sample all nekton that left two saltmarsh impoundments in Louisiana and estimated average emigration to be 21.7 g wet weight·m-2·y-1. Net export from the Louisiana marshes was not known, however, because immigration was not measured (Herke et al. 1992).
Several investigators have estimated the production of a single species within salt marshes (Welsh 1975; Valiela et al. 1977; Meredith and Lotrich 1979; Weinstein 1983), but only a few have estimated the production of an entire saltmarsh fish community
(Schooley 1980). Estimates of immigration and emigration were not necessary in these studies because the species under investigation were marsh residents with limited home range (Welsh 1975; Valiela et al. 1977; Meredith and Lotrich 1979), marsh residents isolated from the estuary within saltmarsh impoundments (Schooley 1980), or transient nekton with marked periods of recruitment so that production could be measured after the recruitment phase (Weinstein 1983).
Despite the potential importance of nekton in energy transfer from the marsh to the estuary, few studies have estimated both estuarine nekton biomass production and export. The boundaries of salt marsh systems are open and ill defined, and the conduits
6 of transport (i.e., creeks) are broad and complex. Thus, estimating the boundaries within which production has occurred, and measuring the exchange of nekton between salt marshes and the estuary, create difficult challenges with respect to sampling.
Open saltmarsh impoundments in East-Central Florida, however, provide unique opportunities for study of marsh systems with respect to aquatic communities. The boundaries between salt marshes and the estuary are clearly defined by a system of dikes, thereby confining nekton into a known area, and the exchange of aquatic organisms is restricted to culverts. Open culverts allow sampling nekton as they move between salt marshes and the adjacent estuary. Although saltmarsh impoundments differ morphologically from natural systems, understanding the function of impounded marsh systems should provide a general model of saltmarsh ecology and linkages to the adjacent estuary by movement of aquatic organisms.
Saltmarsh Impoundments in East-Central Florida
In many areas of the world, salt marshes have been impounded to control water levels within the marsh for a variety of objectives including mosquito control, wildlife enhancement, vegetation mitigation, prevention of saltwater intrusion, reduction of erosion, and prevention of extreme water level fluctuations (Rogers et al. 1994). In East-
Central Florida, the majority of salt marshes were impounded by diking around the perimeter of the salt marsh and installing water control structures (i.e., flapgated culverts and riserboards) to manage water levels for mosquito control, wildlife, and vegetation
(Montague et al. 1985; Montague et al. 1987; Smith and Breininger 1995; Brockmeyer
1997).
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An energy flow diagram that illustrates trophic interactions within saltmarsh impoundments and exchanges with the adjacent estuary is shown in Fig. 1. The sources
(circles), storages (tanks), producers (bullets), and consumers (hexagons) within the impoundment and their interactions are similar for both natural and impounded marshes.
Salt marshes contain a network of creeks, flooded marshes, and open ponds (top left of
Fig. 1, inside the heavy storage tank) that offer habitat for resident nekton. Lines are drawn from the habitat components (ponds, flooded marsh, creeks) to resident nekton to represent the effect of habitat. The resident nekton, in turn, consume and incorporate saltmarsh products (detritus, algae, phytoplankton, benthic invertebrates, and mosquito larvae) into fish biomass. Lines are drawn from the various foods (detritus, algae, phytoplankton, benthic invertebrates, and mosquito larvae) to represent the conversion of these foods to resident nekton.
Saltmarsh creeks and ditches (top left of Fig. 1, inside the storage tank) are adequately deep to be used by adult transient nekton that may exploit both resident and juvenile transient nekton present within the marsh. Other wildlife such as wading birds and reptiles also exploit resident and juvenile transient nekton. The trophic relay is shown in the center of the diagram. Lines are drawn from prey to predators where appropriate. The trophic relay begins with detritus, phytoplankton, and algae, and moves progressively across the diagram left to right towards larger species such as adult transient nekton, wading birds, and reptiles (e.g., alligators, terrapins, and snakes). As larger animals consume smaller animals, the embodied saltmarsh production moves through higher trophic levels, and across the marsh landscape elsewhere. Transient fishes move saltmarsh secondary production to the estuary as they eventually emigrate from the marsh.
8
Reptiles may move saltmarsh secondary production across land boundaries as they access adjacent marshes or the open estuary. Piscivorous birds may move secondary production from the marsh system at even greater scales (regionally, or globally) as they migrate along the Atlantic coast and cross continental boundaries.
Although the fundamental trophic interactions within impoundments are similar to natural systems, the distinguishing features of impounded marshes are the system of dikes and borrow ditches that surround the perimeter of the marsh (Fig. 1, outer outline represents dikes), and the culverts that provide aquatic exchange to the adjacent estuary
(shown at right in Fig. 1). Perimeter ditches within impounded salt marshes, although artificial, are similar to creeks in other marsh systems (lines are drawn from creeks and ditches to nekton to illustrate that both provide nekton habitat). They may provide similar refuge from predation, a conduit for transport of materials from the marsh to the estuary, and access to predators seeking prey when water control structures are open to the estuary
(Gilmore et al. 1982; Rey et al. 1990b).
Exchange of water, detritus, nutrients, and aquatic organisms between the marsh system and the adjacent estuary is confined to culverts (dashed box at right in Fig. 1), where water control structures may be opened or closed depending on management objectives (e.g., resource management, mosquito control). A line drawn from management at top right in Fig. 1 to culverts represents the influence of management in opening or closing the culverts (culverts are indicated as a switch in Fig. 1). A primary concern over saltmarsh impoundments has been the reduction of access to salt marshes by estuarine nekton, especially for transient species that dependent on marshes during early stages of their life history (Montague et al. 1985; Rogers et al. 1994; Brockmeyer et al.
9
1997). Where water level management is not a priority, impoundments can be left open year round to optimize access for wetland-dependent fishes and invertebrates
(Brockmeyer 1997).
Hydrology of Saltmarsh Impoundments in East-Central Florida
When impoundments are open year round, they are directly subject to the hydrology of the adjacent lagoon. Salt marshes in the northern Indian River Lagoon system lie at the extremities of three such lagoons (Indian River Lagoon, Banana River, and Mosquito Lagoon). The waters of these lagoons are isolated from the ocean and have little or no diurnal tidal range (< 5 cm) (Smith 1986). Short-term changes in water levels and circulation are primarily driven by wind. Long-term changes in water levels are dramatically influenced by seasonal variations in sea level. The water levels are typically low in spring and summer, but about 27 cm higher in fall due to thermal expansion and seasonal rainfall (Smith 1986). Due to this seasonal variation in water level, many Indian
River Lagoon marshes are dry during much of summer, but are almost continuously inundated during fall and early winter (Montague et al. 1985).
The hydrology of the northern Indian River Lagoon System may be similar to other seasonally flooded and wind-driven estuaries (e.g., Pamilco Sound, North Carolina;
Laguna Madre, Texas; Camargue, southern France), but differ greatly from more typical tidal marshes such as those in Georgia where daily tides are predictable and tidal range masks seasonal changes in water level. The unique hydrology of the Indian River Lagoon influences saltmarsh use and exchange rates of nekton with the estuary. Use of natural marshes and open saltmarsh impoundments by large juvenile and adult transient species is greatest during high water levels of fall, and use of marshes by young juveniles is
10 greatest during spring (Gilmore et al. 1982; McLaughlin 1982; Rey et al. 1990a, 1990b;
Karlen 1991; Weiher 1995; Poulakis 1996; Lin and Beal 1995; Klassen 1998; Taylor et al. 1998; Faunce and Paperno 1999). Use of saltmarsh impoundments and their ditches by fishes is lowest during summer when water level is low and water temperature and salinities are high. Dissolved oxygen is low under these conditions. Hence, summer water conditions may be suboptimal for many transient fishes (Gilmore et al. 1982; Rey et al. 1990b; Lin and Beal 1995; Klassen 1998).
In contrast to marshes affected by daily tides, the cycle of resident marsh fish migrations to and from the marsh surface in seasonally flooded marshes is expanded over many months, rather than hours. Thus, the movement of saltmarsh resources via the trophic relay would also occur on similar time scales (weeks to months). As in tidal marshes, the trophic relay would also include seasonal movements of nekton from marshes to the estuary as a result of changing habitat preferences as they grow. Direct migration of resident marsh fishes to the estuary may be especially important in the Indian
River Lagoon system where hydrology is seasonal and the relatively narrow marshes are in close proximity to open estuarine waters.
Consumption and Migration of Fish Biomass from the Salt Marsh
The artificial boundaries, creeks, and connections to the estuary, together with the seasonal hydrology associated with open saltmarsh impoundments in the Indian River
Lagoon, permit a biomass budget of saltmarsh fishes to be constructed (Fig. 2). Outputs from the standing stock of nekton within the impoundment are the result of emigration and predation/death. Inputs to the standing stock of nekton within the impoundment are the result of immigration and production. Monthly estimates of standing stock,
11 immigration, emigration, and predation can be used to estimate annual production of fishes in the saltmarsh (production equals change in biomass divided by change in time minus immigration plus emigration plus consumption by predators). This estimate of saltmarsh fish production can be compared to those of other locations and other estuarine habitats such as seagrass beds and open estuarine waters. More importantly, the yield to predatory fish, birds, and emigration can be quantified.
Management and Restoration of Impoundments
The patterns of fish use and predator abundance within seasonally flooded salt marshes, and the consumption and migration of fish biomass from the marsh are relevant to management and restoration of saltmarsh impoundments in the Indian River Lagoon,
Florida. Almost all salt marshes in the Indian River Lagoon system have been impounded, and over 65% of saltmarsh impoundments (by area) are located within
Merritt Island National Wildlife Refuge (MINWR) (Brockmeyer et al. 1997). Thus, management and restoration activities within the refuge potentially influence the entire
Indian River Lagoon system.
The impoundment situation in the Indian River Lagoon system, and MINWR in particular, was an appropriate study area to meet the objectives of the U.S. Geological
Survey Coastal Restoration Initiative. The goal of the Coastal Restoration Initiative was to develop fundamental knowledge of community ecology to guide restoration strategies for engineered salt marshes to maintain species biodiversity and ecosystem integrity. To interpret the consequences to fish production by various impoundment restoration alternatives, a comparison of fish use among perimeter ditches, marsh surface, marsh creeks, and estuarine shorelines was needed, because each will be affected by restoration
12
efforts. Thus, scientific knowledge developed regarding saltmarsh trophic interactions,
fish migrations, and differential fish use among marsh habitats have direct applications to
contemporary resource management objectives.
Hypotheses – Resident Migrations
During the seasonal high water period (July – November), resident fishes are
dispersed on the marsh surface where they make use of abundant food and spawning
sites. As water levels seasonally recede (December – February), resident fishes leave the
marsh surface, entering marsh creeks and ditches to escape desiccation.
Resident Fish Hypothesis 1 (Fig. 3): A portion of the resident fish population
emigrates from the impoundment contributing marsh production to the estuarine food
chain. Resident marsh fishes such as Cyprinodon variegatus, Gambusia holbrooki, and
Poecilia latipinna are concentrated into ditches and creeks as water levels recede. If crowding occurs, some of the resident fishes may leave the impoundment in search of additional forage. During strong winds and rain that drive water exchange through culverts, some resident fishes may be forced from the impoundment to the estuary. These resident fishes add to the forage of larger estuarine fishes.
Resident Fish Hypothesis 2 (Fig. 4): Resident fishes remain within the
impoundment and few individuals move into the estuary. The creeks and perimeter
ditches within the marsh offer adequate food and the relatively deep waters and the high
edge/open water ratio provide refuge from predation by wading birds and aquatic
predators. The resident fishes do not leave the refuge of these impoundment creeks and
ditches and can avoid export through culverts during periods of high current velocity.
Previous studies conducted in tidal marshes have shown that resident fish densities are
13 high along creek edges, especially during low tide (Valiela et al. 1977; Meredith and
Lotrich 1979; Peterson and Turner 1994). In such marshes, however, fish will again have access to the marsh surface in a matter of hours when the tide rises. This situation differs from the Indian River Lagoon where the marsh surface may remain dry up to several months.
Hypotheses – Trophic Relay by Transient Fishes
Juvenile Transient Fish Hypothesis 1 (Fig. 5): Juvenile transient fish enter the impoundment, grow, and eventually emigrate to the estuary in greater biomass (although fewer individuals) than when they entered. Large Piscivorous Fish Hypothesis 1 (not figured): Large predatory transient fish enter the impoundment, prey upon saltmarsh fish
(residents and small transients), then leave. Young transient fish enter saltmarsh impoundments, either actively as juveniles, or passively as larvae, during periods of high current velocity through culverts. Young transient fish not only enter the impoundments, but also some survive and eventually emigrate from the impoundment to the estuary.
Exported fish biomass may be greater than that imported. Juvenile fish abundance
(no.·m-2) within the impoundment equals or exceeds that outside the impoundment, if juveniles seek saltmarsh habitat. Large predatory fish enter the impoundment to feed upon resident and small transient saltmarsh fish, then leave.
Juvenile Transient Fish Hypothesis 2 (Fig. 6): Juvenile transient fish are abundant along estuary shorelines, but absent from impounded marshes. Large
Piscivorous Fish Hypothesis 2 (not figured): Large predatory transients are abundant along estuary shorelines, but absent from impounded marshes. Transient fish seldom enter the impoundment, but are more often found along the estuary shoreline among
14 saltmarsh vegetation. Estuary shorelines may be the preferred habitat for transient fishes.
They may avoid impoundments because water quality is too poor, or because food and cover are greater along the estuary shoreline. Transient fish densities (no.·m-2, g·m-2) are greater along the shoreline than within the impoundment ditches and creeks.
Although studies report the occurrence of transient fishes in impoundments when they are open to the estuary (Gilmore et al. 1982; McLaughlin 1982; Rey et al. 1990a, 1990b,
Karlen 1991; Weiher 1995; Poulakis 1996; Lin and Beal 1995; Klassen 1998; Taylor et al. 1998; Faunce and Paperno 1999), few compare fish densities in impoundments with those along the estuary shoreline and seagrass beds (Klassen 1998). Klassen (1998) found that an estuary shoreline in Mosquito Lagoon, Florida, provided a different type of habitat for transient fishes than within an impoundment. For example, Leiostomus xanthurus was more abundant along the shoreline adjacent to an impoundment than inside the impoundment. Also, several species Cynoscion nebulosus, Lagodon rhomboides, Strongylura marina, and Symphurus plagiusa) collected along the shoreline were absent from collections within the impoundment (Klassen 1998).
Juvenile Transient Fish Hypothesis 3 (Fig. 7): Saltmarsh impoundments act as a
“sink” for juvenile fish. Juvenile transients enter the impoundment but most do not leave.
Large Piscivorous Fish Hypothesis 3 (not figured): Large predatory fish do not survive well in saltmarsh impoundments. Fish are trapped within the wetland and die from either poor water quality or predation by birds and other wildlife such as alligators. Biomass of juvenile fish is not exported to the estuary greater than that of the earlier immigrating juvenile fish. The artificial accessibility to marshes provided by perimeter ditches may expose transient fish to poor water quality associated with seasonally flooded marshes
15
(Poizat et al. 1997). The openness of natural creeks, embayments, and estuarine
shorelines may be necessary for juvenile survival and predatory fish access. Such
openness may offer greater opportunity for transient species to escape the marsh during
poor water quality conditions. Culverts may restrict access because of smaller size of
their opening relative to complete dike removal.
These three hypotheses regarding transient fish use of Indian River Lagoon
marshes are not mutually exclusive. Although transient fishes have often been reported
to use salt marshes as nursery habitat, considerable debate exists (e.g., Miller et al. 1984).
Also, transient fish occurrence within salt marshes varies among species. Some species
use the Indian River Lagoon saltmarsh creeks and ditches (e.g., Mugil cephalus; Klassen
1998), while others may occur only along the estuary shoreline (e.g., L. xanthurus;
Klassen 1998). Which hypothesis is supported by analyses may ultimately depend on the
available suite of transient species present in the estuary adjacent to the study marshes.
The proposed transient hypotheses may depend upon which resident hypothesis
transpires. For example, large transient fishes that prey on residents may benefit from
concentrated food if residents remain within the impoundment for several months after
water levels recede during late winter. Young transients entering the impoundment in
spring, however, would face severe competition with resident marsh fishes, resulting in
less available food and space. If, however, resident fishes leave the impoundment after
water levels recede from the marsh surface during late winter, then competition between
residents and young transients in the ditches and creeks during spring may be much
lower, possibly resulting in greater transient survival and growth.
16
Fig. 1. Energy flow diagram illustrating trophic interactions within a saltmarsh impoundment and exchanges with the adjacent estuary. Outer outline represents the dikes that define the impoundment border. Bold outline contains within it some fundamental trophic interactions found in all flooded marshes. Bold dashed box at right contains aquatic sources that are exchanged with the impoundment. Ditches, culverts, and perimeter dikes (impoundment boundary) are unique to impounded salt marshes.
Immigration EmigrationEmigration
Standing Stock
Production Predation 17
Fig. 2. Nekton biomass budget in a saltmarsh impoundment: Production = ∆standing stock / ∆time – immigration + emigration + predation
Resident Hypothesis 1
a
Dike
Marsh Surface Culvert
EstuaryDitch Impoundment
b
Dike 18
Marsh Surface Culvert
EstuaryDitch Impoundment
Fig. 3. Illustration of Resident Hypothesis 1: As seasonal water level recedes (b), resident fishes are concentrated into subtidal habitats within the marsh (creeks and ditches). A portion of the resident fish population leaves the impoundment, contributing to the estuary prey base. a) Seasonal High Water (July – February) b) Seasonal Low Water (February – July). Arrows indicate net direction of travel by fishes.
Resident Hypothesis 2
a Dike
Marsh Surface Culvert
Ditch Estuary Impoundment
b Dike 19
Marsh Surface Culvert
EstuaryDitch Impoundment
Fig. 4. Illustration of Resident Hypothesis 2: As water level recedes (b), resident fishes are concentrated into subtidal habitats within the marsh (creeks and ditches) and few leave the impoundment. a) Seasonal High Water (July – February) b) Seasonal Low Water (February – July).
Juvenile Transient Hypothesis 1
a Dike
Marsh Surface Culvert
Estuary Impoundment Ditch 20 Dike b
Marsh Surface Culvert
Estuary Impoundment Ditch
Fig. 5. Illustration of Juvenile Transient Hypothesis 1: Juvenile transient fishes (small fish shown in ‘a’) enter the impoundment, grow, (large fish shown in ‘b’) and some eventually emigrate to the estuary. More biomass may leave than entered (although fewer individuals). a) Seasonal High Water (July – February) b) Seasonal Low Water (February – July). Arrows indicate net direction of travel by fishes.
Juvenile Transient Hypothesis 2
a Dike
Marsh Surface Culvert
Estuary Impoundment Ditch
Dike
b 21
Marsh Surface Culvert
Ditch Estuary Impoundment
Fig. 6. Illustration of Juvenile Transient Hypothesis 2: Juvenile transient fishes are abundant along estuary shorelines, but absent from impounded marshes. a) Seasonal High Water (July – February) b) Seasonal Low Water (February – July). Small fish in ‘a’ indicate young fish. Large fish in ‘b’ indicate fish that have grown.
Juvenile Transient Hypothesis 3
a
Dike
Marsh Surface Culvert
Estuary Impoundment Ditch
b
Dike 22
Marsh Surface Culvert
EstuaryDitch Impoundment
Fig. 7. Illustration of Juvenile Transient Hypothesis 3: Impounded marshes are a sink for juvenile transient fishes. Juvenile transients enter the impoundment, but most do not leave. a) Seasonal High Water (July – February) b) Seasonal Low Water (February – July). Arrows indicate net direction of travel by fishes. Small fish in ‘a’ indicate young fish. Large fish in ‘b’ indicate fish that have grown.
CHAPTER 2 FIELD METHODS
Study Area
Merritt Island National Wildlife Refuge (Fig. 8), lies along the transition between temperate and subtropical climate in Florida where mangroves and salt marsh alternate in response to periodic freezes that reset mangrove development (Kangas and Lugo 1990;
Stevens 1999). Saltmarsh plant species covered the marshes after consecutive freezes in the 1980s killed existing mangrove forests consisting of some Rhizophora mangle, and many Avicennia germinans and Laguncularia racemosa. However, dead mangrove wood and fringing live L. racemosa remain conspicuous features of the estuarine shorelines.
The vegetation typical of seasonally flooded marshes at Merritt Island consists of
Distichlis spicata, Paspalum vaginatum, Batis maritima, and Spartina bakerii (Montague et al. 1985). Spartina alterniflora may fringe the estuary shoreline, but is seldom found on the marsh surface. Merritt Island’s transitional location enhances the diversity of nekton communities, as both temperate and subtropical fish species co-exist (Snelson
1983).
The selection criteria for the study impoundment included the following: the impoundment was located within Banana Creek where joint University of Florida and
U.S. Geological Survey fish community research was ongoing, the impoundment was covered by saltmarsh vegetation indicative of Merritt Island (as opposed to exotic marsh plants or predominately upland species), culverts were open year round to allow the
23 24
exchange of aquatic organisms between the impoundment and the estuary, the culverts
had been open for several years so the ecological community was not undergoing
dramatic successional changes during the study period, and adequate access to the
impoundment by project personnel was available throughout the course of the study.
The impoundment selected for study was C20C (134 ha) located in Banana Creek
across from the Kennedy Space Center shuttle landing facility and adjacent to the KSC
Vehicle Assembly Building (Fig. 9). The impoundment saltmarsh vegetation is
dominated by D. spicata and P. vaginatum, which are typical saltmarsh species found in
the vicinity of Merritt Island (Fig. 10). A perimeter ditch (approximately 10 m wide and
1 m deep) separates the dike from the interior of the impoundment and a major creek,
“Drainout Creek”, is located within the impoundment (Fig. 10). L. racemosa fringes the estuarine shoreline, Drainout Creek, and the perimeter ditch. In addition to live L. racemosa, the estuary shoreline is fringed by decaying wood from dead mangroves and a narrow band (1 – 3 m) of S. alterniflora often occurs seaward of live white mangroves.
Sediments are soft, especially within the perimeter ditch and Drainout Creek. Sediments along the estuary shoreline consist of firm mud within embayments and a mixture of mud and sand in areas directly adjacent to Banana Creek.
Impoundment C20C is connected to the Banana Creek estuary by four sets of 0.91 m diameter culverts (Fig. 10). Each set consists of one culvert with riser boards, and one culvert with a flapgate. These water control structures enable resource managers to manipulate water levels within the impoundment when desired, but no manipulation was undertaken over the course of this study. The flapgate allows water to enter the impoundment when lagoon water levels exceed those in the impoundment. Riser boards
25
(each about 15 cm high) can be added or removed as needed to maintain a desired water level. If the impoundment water level exceeds the riser boards, then water will spill over the boards into the estuary.
There are eight culverts connecting the impoundment directly to Banana Creek
(Fig. 10). Two additional culverts are located within the impoundment; one connects
C20C to an adjacent creek, and the other connects C20C to a small ditch at the southern end of the impoundment (Fig. 10). These two culverts were closed during the study, but the remaining eight were open (flapgate open and riserboards removed), providing estuarine communication with the impoundment. Lights used to guide the space shuttle to the landing facility are located along a boardwalk that extends across the southwestern portion of the impoundment. Hence, adequate access to the impoundment was available by project personnel because the US National Aeronautics and Space Administration
(NASA) must maintain the dike roads surrounding the impoundment for maintenance of the lights.
A list of common names of all animal and plant species cited in this study is shown in Table 1. For clarity, the following definitions regarding habitat and fish classifications are provided (Table 2). Salt marsh (natural or impounded) refers to the dominant marsh area that is located behind the estuary/marsh berm, or impoundment dikes, indicative of the Indian River Lagoon marshes. Estuary/marsh berm is a natural levee located at the outer mean high water mark (Provost 1973), and is the location where dikes were constructed during marsh impoundment (Montague et al. 1985). Salt marsh as defined here includes the vegetated marsh surface, tidal creeks that penetrate the salt marsh plane, marsh islands, and perimeter ditches if the marsh is impounded. Indian
26
River Lagoon estuary refers to the Indian River Lagoon, Banana River, Banana Creek, and Mosquito Lagoon (see Fig. 8). The estuary typically includes open water areas and seagrass flats between the barrier island and mainland, intracoastal waterways, and the shoreline up to the estuary/marsh berm (or impoundment dike).
Saltmarsh fishes refer to the entire suite of resident, transient, and incidental fishes present within the salt marsh. Incidental fishes are those species resident in the estuary and occasionally occur in salt marshes by accident, or as a negligible extension to their regular habitat (usually seagrass-associated fishes). These species do not use the salt marshes as nursery habitat for young or as regular feeding areas for adults, but more typically use estuary habitats. Examples include anchovies, gobies, and pipefish.
Water Conditions
To determine short-term and seasonal variation in water conditions within the impoundment relative to the adjacent estuary, water level (m), temperature (ºC), salinity
(‰), dissolved oxygen (mg·L-1), turbidity (NTU), and oxygen redox potential (Eh) were monitored hourly with two continuously deployed datasondes (Hydrolab Datasonde 3); one within the impoundment and one in Banana Creek adjacent to the impoundment (Fig.
10). The datasondes were calibrated prior to deployment and twice during the study period in accordance with the manufacturer’s recommended procedures. Impoundment water level was recorded to within the nearest 0.3 cm from a permanent staff gauge within the impoundment. Water level measurements taken by the datasondes were corrected to correspond to water level readings on the permanent staff gauge. This was accomplished by taking the difference between datasonde water-level readings and observed readings on the impoundment staff gauge during three periods of little wind,
27 water flow, rainfall, and water level changes. These differences were averaged to determine a correction factor. The impoundment staff gauge was later surveyed by
NASA personnel, which provided a correction with respect to the 1988 National Geodetic
Vertical Datum (NGVD).
Fish Standing Stock
Standing stock, immigration, emigration, and predator abundance (by large fishes and also piscivorous birds) were sampled monthly for a period of one year beginning July
2000 and ending July 2001 (Table 3). The monthly sample usually required one week to complete. Small fishes in the impoundment and along the adjacent Banana Creek shoreline were quantified with a 1.15 m (4 ft) radius, 6 mm (1/4 inch) bar mesh, monofilament cast net. Cast nets have been used by commercial fisherman along the
Indian River Lagoon to target fast-moving species such as mullet, and are often used to capture bait for recreational fishing (Schoor et al. 1995). Cast nets can be quickly deployed and cleared of fish, an advantage over other gear types such as drop and throw traps requiring long processing times to clear fish from the gear. Thus, more deployments can be made and more area covered with cast nets than with drop and throw traps, which improves the chances of finding relatively rare species such as juvenile transients. Also, cast nets can be easily deployed by casting from the shoreline or from a small boat, thereby allowing the perimeter ditches and marsh creeks to be sampled effectively without fixed boardwalks that are necessary when sampling impoundments with seines
(Gilmore et al. 1982). The diameter and mesh size of the cast net were chosen because the small diameter is manageable to throw, thereby reducing variation in deployment
28 area, and the mesh size is effective for capturing juvenile fishes (Woodward 1989). Only areas of low vegetation density can be sampled effectively without fouling.
The cast net was deployed among the primary habitats associated with both transient juvenile fishes and resident nekton. The areas sampled monthly with the cast net were the impoundment ditch (ca. 1 m depth), and creek (ca. 1 m depth). The estuary shoreline (< 1 m depth) was also sampled for comparison with the impoundment ditch and creek. The estuary shoreline was sampled along the dike within at least 1 m of the emergent shoreline vegetation and often within low-density smooth cordgrass. The seasonally flooded marsh surface (< 0.5 m depth) was sampled during July 2000 (the onset of marsh flooding), and October 2000 (the time of seasonally high water). The marsh surface consisted of consolidated mud substrate, emergent vegetation, open water ponds, and small potholes (2 – 3 m diameter). The marsh surface was sampled in open water areas near emergent vegetation and within small potholes. Deeper pools within the marsh were also sampled during January 2001 (after water had receded from the marsh) to measure the density of any fish remaining in ponded water.
A pilot study conducted during March 2000 determined that a minimum of 14 cast net deployments were needed to detect a statistical difference between the mean numbers of fish from each habitat (α = 0.05, β = 0.90; Sokal and Rohlf 1995). Each habitat type
(Drainout Creek, perimeter ditch, marsh surface, and estuary shoreline) was mapped using aerial photography (USGS 1995). The 14 cast-net deployment stations along the estuary shoreline were selected by randomly choosing among 136 sampling points spaced
16 m apart along the perimeter dike. The 14 stations in the perimeter ditch were selected by randomly choosing from among 98 sampling points (a 615 m segment of the perimeter
29
ditch was excluded due to inaccessibility) spaced 16 m apart along the centerline of the
perimeter ditch. For the Drainout Creek sampling, 14 points from among 55 potential
sampling points (30 m apart) were selected for cast net deployment. For the marsh
surface sampling, 14 points were chosen in areas of low vegetation density and depth of
at least 10 cm (knotgrass marsh/shallow ponds; Fig. 10).
A small jon boat equipped with an electric trolling motor was used to access the
perimeter ditch, creek, and estuary shoreline for cast net deployment. For the estuary
shoreline sampling, the cast net was deployed as close to the shoreline as possible without
fouling the net in wood debris or overhanging trees. For perimeter ditch sampling, a coin
was tossed prior to each cast net deployment to determine whether to cast the net along
the edge or near the center of the ditch. Collected fish were identified to species, counted,
measured (total length), and released. Weight was later determined from length-weight
relationships, which are given in Appendix A. Cast nets occasionally capture large fish
(> 150 mm total length). Fish larger than 150 mm total length were excluded from the
cast net analysis because they were better represented in gill net catches (see piscivorous
fish section).
Cast-net deployment area was estimated by throwing the net 14 times from the
bow of a jon boat onto a grass surface (on land). The shape of the net after landing
approximated an ellipse. The deployment area was estimated from the area formula for
an ellipse (π·½ major axis length·½ minor axis length). The 14 calculated areas were averaged. Cast net sampling data were reported as fish·m-2.
30
Fish Ingress/Egress
Culverts isolated the ingress and egress of fishes to specific pathways, which provided an opportunity to quantify fish movements between coastal wetlands and the adjacent estuary using culvert traps. Culvert traps are oversized minnow traps with a dividing screen placed at the center so that the direction of movement of captured fish can be determined (Gilmore et al. 1982). Although culvert nets have been used in previous impoundment studies (e.g., Weiher 1995), such nets only capture fish moving with current. Culvert traps have the added advantage of capturing fish moving against the current. A modified version of the stainless steel culvert trap used by Gilmore et al.
(1982), Rey et al. (1990a), and Taylor et al. (1998) was constructed using typical fish trap material (plastic coated wire and 0.25 cm bar mesh Vexar). The traps were 80 cm in diameter, which was slightly smaller than the diameter of the culverts (91 cm diameter) to account for fouling organism growth inside the culverts. The opening of the culvert trap was 42 cm high by 8 cm wide, and the typical gap between the culvert trap and the sides of the fouled culvert walls was 2 cm. Four culvert traps were available to document fish movements.
Culvert trap sampling was conducted for four days and four nights continuously each month for one year (Table 3). One culvert trap was placed at each culvert location
(culvert locations 1 – 4; see Fig. 10). Two culverts are present at each culvert location, but only one was sampled with the trap, the other remained unobstructed. Captured fish within the culvert traps were removed twice per day (early morning, and late afternoon) except if detrital fouling necessitated more frequent processing to keep the traps clear.
Water flow through the culverts was measured with a flow meter during each nekton
31 collection before and after the culvert trap was installed inside the culvert. Collected fish were identified to species, and their direction of travel recorded. Fish were counted, measured (mm total length), and released in the direction they were traveling. Weights were determined from length-weight relationships. Numerical and biomass culvert trap catches were reported as fish·culvert-1·hr-1.
A separate study was conducted during July 2001 to determine if fished and adjacent unfished culverts differed in fish passage rates. There is one flapgate and one riserboard culvert at each culvert location (see Fig. 10), but only one is fished with a culvert trap. When a culvert trap was added to a culvert, the current through the culvert was reduced by about 50%, while current in the adjacent culvert (unfished) remained the same. To simulate this condition, both culverts at a location were fished simultaneously.
One trap was fitted with an additional dividing screen to reduce the flow by 50% relative to the adjacent culvert. After fishing the culverts for two days and two nights, the trap with the added dividing screen and the unmodified trap were switched, and then fished for an additional two days and two nights. This test was repeated at each of two culvert locations (culvert location 1 and 4; see Fig. 10).
A study testing the retention efficiency of the culvert traps was also conducted during July 2001. Fish were caught by cast net, fin-clipped, and added to culvert traps.
The number of fin-clipped fish remaining in the traps at the end of the sets relative to the number that were added represented the retention efficiency of the traps. Approximately
20 fin-clipped fish (species common at time of collection) were added to each of two culvert traps (one trap at culvert location 1, and one trap at culvert location 4; see Fig. 10) and left for 10 – 14 hrs. At the end of the set, the number of fin-clipped fish remaining in
32
the trap was counted. This procedure was repeated nine times in one culvert trap and 11
in the second trap (n = 20 replicates total).
Piscivores
Large transient fish within impoundments and the adjacent lagoon were sampled
with gill nets to estimate the abundance of potential predators of resident and juvenile
transient nekton (Table 3). Gill nets, 38 mm (1.5 inch) monofilament bar mesh, were
deployed at permanent stations where the nets could be easily set, observed, and retrieved
(typically near culvert locations; Fig. 11). The nets were 1.2 m high, and the depth of the
water in which they were fished ranged from 0.5 – 1 m. Gill nets were set in the
impoundment ditch (four 10 m net sections), the impoundment creek (one 30 m net), and
the Banana Creek shoreline (two 30 m nets). The nets deployed in the ditch were
stretched across the ditch, those along the estuary shoreline were oriented perpendicular
to the shoreline, and the net in the creek was run from culvert location 1 along the
centerline of the creek perpendicular to the creek shoreline. Each net was deployed one
day each month (for one year) for two to three hours between 1700 – 2100 Eastern
Standard Time, and checked for fish every 30 minutes during deployment. The perimeter
ditch and creek gill nets were deployed, checked for fish, and retrieved using a small jon
boat to minimize disturbance to the soft sediments. The shoreline gill nets were
deployed, checked for fish, and retrieved by wading along the gill net. Weights of
piscivorous fish were determined from length-weight relationships.
Large fish (greater than about 800 mm total length) such Megalops atlanticus,
Pogonias cromis, and Sciaenops ocellatus broke through the 38 mm bar mesh monofilament nets during the estuary shoreline sets and were not assessed by this method.
33
Attempts to use larger 50 mm bar mesh nets were thwarted by the occurrence of large alligators, which broke through the 38 mm bar mesh, but would entangle in the larger 50 mm bar mesh.
All uninjured fish captured by gill net were fin-clipped, measured, and released.
Fish injured during gill net capture were frozen whole and returned to the laboratory for stomach content analysis. Number and biomass data for gill net samples were reported as catch per unit effort (fish·10 m net-1·hr-1). Catch per unit effort was standardized to a 10 m net length by dividing the fish catch by the number of 10 m sections fished (10 m of net deployed at each ditch location, and 30 m (i.e., three 10 meter sections) of net deployed at the creek and each estuary shoreline location).
Other potential predators of resident and juvenile transient nekton were piscivorous birds such as wading birds and diving birds. Piscivorous bird abundance was determined by visual surveys. Piscivorous birds within the impoundment were identified and counted by visual survey taken from the dike road between 0700 – 0900 Eastern
Standard Time twice during each month. Birds along the estuary shoreline adjacent to the impoundment (within 20 m of the dike) were counted separately. Bird biomass was determined from estimates of adult birds given for each species (Terres 1980). Number and biomass of piscivorous birds were reported as birds·impoundment-1·d-1.
Statistical Analysis
Pearson’s correlation was used to test for linear relationships among monthly mean animal catches and water conditions. Water conditions included in the correlation were temperature, salinity, dissolved oxygen, turbidity, and culvert water flow. Animal catches included in the correlation were fish standing stock (monthly averages of all
34 species combined from cast net catches), net fish ingress (monthly averages of all species combined from culvert trap catches), piscivorous fishes (monthly averages of all piscivores in gill net catches), and piscivorous birds (monthly averages of all piscivorous birds in bird counts). Also included were the monthly averages of the four most common small species (caught in cast nets and culvert traps) and the four most common species caught in gill nets. In addition to Pearson’s correlation, Spearman’s rank correlation was used to test for nonlinear relationships among the same variables.
Fish standing stock, net fish ingress, piscivorous fish, and piscivorous bird results were plotted, and differences among months were analyzed graphically. Standing stock
(cast net) data were log transformed and months pooled. Comparisons of fish density among the various habitats sampled (perimeter ditch, creek, and estuary shoreline) were then performed using analysis of variance. Significant differences were analyzed further by Tukey’s pairwise comparisons. These statistical analyses were performed for resident and transient fishes separately (number and biomass). Length frequency plots were constructed for species where more than 100 individuals were collected.
For net fish ingress, piscivorous fish, and piscivorous bird results, differences among habitats (pooling months) were compared with Kruskal-Wallis One-Way Analysis of Variance. Significant differences were analyzed further with Wilcoxon signed-rank tests adjusting p-values to avoid an inflated overall level of significance (p-value·number of pairwise comparisons; Sokal and Rohlf 1995). For net fish migration, these analyses were performed for both resident and transient fish separately (numerical and biomass).
All statistical analyses were performed with Systat 8.0 (SPSS) software.
Table 1. Species cited in this study.
Species Common Name Species Common Name
Fishes and Invertebrates*
Alpheus heterochaelis snapping shrimp Hippocampus erectus lined seahorse Anchoa mitchilli bay anchovy Hippocampus reidi longsnout seahorse Arius felis hardhead catfish Jordanella floridae flagfish Bairdiella chrysoura silver perch Lagodon rhomboides pinfish Brevoortia smithi yellowfin menhaden Leiostomus xanthurus spot Brevoortia patronis gulf menhaden Lepisosteus platyrhincus Florida gar Callinectes sapidus blue crab Lepomis macrochirus bluegill Centropomis undecimalis common snook Lucania parva rainwater killifish 35 Chasmodes bosquianus striped blenny Megalops atlanticus tarpon Chilomycterus schoepfi striped burrfish Menidia peninsulae tidewater silverside Caranx hippos crevalle jack Microgobius gulosus clown goby Cynoscion nebulosus spotted seatrout Micropogonias undulatus Atlantic croaker Cyprinidon variegatus sheepshead minnow Mugil cephalus striped mullet Dasyatis sabina Atlantic stingray Palaemonetes pugio grass shrimp Diapterus auratus Irish pompano Penaeus aztecus brown shrimp Elops saurus ladyfish Pogonias chromis black drum Eucinostomus argenteus spotfin mojarra Poecilia latipinna sailfin molly Floridichthys carpio goldspotted killifish Sciaenops ocellatus red drum Fundulus confluentus marsh killifish Sphoeroides nephelus southern puffer Fundulus grandis gulf killifish Strongylura marina Atlantic needlefish Fundulus heteroclitus mummichog Strongylura notata redfin needlefish Gambusia holbrooki eastern mosquitofish Symphurus plagiusa blackcheek tonguefish Gobiosoma bosc naked goby Syngnathus scovelli gulf pipefish Gobiosoma robustum code goby Trinectes maculatus hogchoker
Table 1. Continued
Birds
Ajaia ajaja roseate spoonbill Hydranassa tricolor Louisiana heron Anhinga anhinga American anhinga Megaceryle alcyon belted kingfisher Ardea herodias great blue heron Mycteria americana wood stork Butorides striatus green heron Nycticorax nycticorax black-crowned night heron Casmerodius albus great egret Pandion haliaetus osprey Dichromanassa rufescens reddish egret Pelecanus erythrorhynchos white pelican Egretta thula snowy egret Pelecanus occidentalis brown pelican Eudocimus albus white ibis Phalacrocorax auritus double-crested cormorant Florida caerulea little blue heron Plegadis falcinellus glossy ibis Himantopus mexicanus black-necked stilt
Reptiles 36
Alligator mississipiensis American alligator Malaclemys terrapin diamondback terrapin
Mammals
Dasypus novemcinctus armadillo Sus scorfa feral hogs Lynx rufus floridanus bobcat Trichechus manatus manatee Procyon lotor raccoon
Vegetation
Avicennia germinans Black mangrove Paspalum vaginatum knotgrass Batis maritima saltwort Rhizophora mangle Red mangrove Distichlis spicata saltgrass Spartina alterniflora smooth cordgrass Laguncularia racemosa White mangrove Spartina bakerii bunch cordgrass
*American Fisheries Society official common names
Table 2. Terms used to describe various places, habitats, and species.
Term Definition
Salt marsh/Impoundment Dominant area located behind the estuary/marsh berm, or impoundment dikes. Includes the vegetated marsh surface, creeks that penetrate the marsh plane, marsh islands, and perimeter ditches if the marsh is impounded.
Indian River Lagoon estuary Indian River Lagoon, Banana River, Banana Creek, and Mosquito Lagoon Includes open water areas, seagrass flats, intracoastal waterway, and shoreline up to the estuary/marsh berm
Resident species Species that complete their life cycle within the salt marsh.
Transient species Species that use salt marshes during some portion of their life cycle 37 either as nursery habitat for young or as regular feeding areas as adults.
Incidental species Species resident to the estuary and occasionally occur in salt marshes by accident, or as a negligable extension of their regular habitat (usually seagrass- associated species).
Saltmarsh fishes Collection of resident, transient, and incidental fishes within the salt marsh.
Table 3. Summary of monthly gear deployments.
Number of Deployments (2000 - 2001) Biomass Budget Gear Type and Habitat Parameter Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Standing Cast net - drainout creek 14 14 14 14 14 14 14 14 14 14 14 14 168 Stock Cast net - perimeter ditch 141414141414141414141414168 Cast net - estuary shoreline141414141414141414141414168 Cast net - marsh surface 14 14 14 36
Imigration/ Culvert trap - days 4 4 4 3* 4 4 4 4 4 3* 4 4 46 EmigrationCulvert trap - nights 4444444443*4447 38 Fish Predation Gill net - drainout creek 11111111111112 Gill net - estuary shoreline 22222222222224 Gill net - perimeter ditch 33333333333336
Bird Predation Morning bird counts 22222222222224
*Limited by security concerns within NASA (i.e., shuttle launches)
39
Fig. 8. Location of study site (Banana Creek) within the northern Indian River Lagoon system
40
Vehicle Assembly Building
Shuttle Landing Facility Estuary shoreline
Drainout Creek Banana Creek
Impoundment C20C
Impoundment C20A
Fig. 9. Map of Impoundment C20C within Kennedy Space Center.
41
Banana Creek Highway 3
Dike Road Drainout Creek
F R
Boardwalk to F R NASA lights 1
2
Impoundment F 3 C20C R
F 4 R
R
Legend
Dike Road Creek R Creek/Ditch
Knotgrass Marsh/Shallow Ponds
White Mangrove/Brazilian Pepper Impoundment Uplands/High Wetlands C20A Cattail Marsh
F Flapgated Culvert R R Riserboard Culvert
n Culvert Location
Datasonde Location
Fig. 10. Map of Impoundment C20C showing vegetation types, culvert locations, and datasonde locations.
42
Estuary
Drainout Creek
Ditch
Ditch
Estuary Ditch
Fig. 11. Gill net deployment locations within Impoundment C20C. Lines indicate orientation of gill nets.
CHAPTER 3 FIELD RESULTS
Water Conditions
Water levels during the study period were lowest during late winter/early spring and highest during fall (Fig. 12). During summer, water level oscillated near marsh elevation, periodically flooding the marsh for one to two weeks. The marsh was continuously flooded beginning in July 2000 and ending in December 2000 (six months).
Over the course of the study, water level ranged between 0.2 and 0.8 m NGVD.
Maximum water temperature (Fig. 13) during summer exceeded 35 °C, and minimum temperature in winter fell below 10 °C. Water temperature varied diurnally (Fig. 14), with maximum temperatures occurring late in the day. Salinity (Fig. 15) fluctuated dramatically, particularly during spring through fall. A series of low salinity pulses occurred near the end of the study (May through July 2001). Minimum salinities during the record were about 10 ‰, and maximum salinities exceeded 40 ‰. Annually, dissolved oxygen and redox potential (Figs. 16 and 17, respectively) were highest during fall and winter and lowest during summer. Although temperature and salinity were similar between Impoundment C20C and Banana Creek, dissolved oxygen and redox potential reached higher levels in Banana Creek during the day, and dissolved oxygen and redox potential were consistently lower in the impoundment. Both dissolved oxygen and redox potential varied diurnally (Figs. 18 and 19, repectively), with maximum daily dissolved oxygen (~5 mg·L-1) and redox potential (~400 mV) occurring late in the day,
43 44
and minimum values (near 0 mg·L-1 and < 100 mV) occurring during morning hours.
The two sudden breaks in the pH record (Fig. 20) corresponded to calibrations of the
instrument. pH varied diurnally (Fig. 21), with maximum pH levels occurring near the
end of the day, and minimum pH levels occurring during morning. Thus, overall diurnal
pattern is minimum dissolved oxygen, redox potential, and pH each morning, which
represent the most limiting combination of water conditions with respect to nekton.
These limiting conditions, however, only occur for a few hours each day.
Average water flow through culverts at Impoundment C20C measured during
culvert trap sampling (measurements were taken prior to each culvert trap deployment)
varied among months (Fig. 22). Water was moving into the impoundment through
culverts at 10 – 30 cm·s-1 at the onset of marsh flooding in July 2000 and again during a
flooding event in March 2001. Water was moving out of the impoundment through
culverts at about 10 cm·s-1 during September and October 2000, and April, May, and
June 2001.
Patterns of Fish Use and Piscivore Abundance within the Salt Marsh
The average area (± SD) of 14 cast net deployments was 2.8 ± 0.2 m-2. Catch in
each cast net deployment was divided by 2.8 to give abundance or biomass·m-2.
Comparing standing stock of fishes, migration by fishes, piscivorous fish catch per unit effort, and piscivorous bird abundance revealed a seasonal pattern of fish use and predator abundance within the impoundment (Figs. 23 and 24). At the onset of marsh flooding, net fish ingress occurred (July in Figs. 23b and 24b). Piscivorous bird abundance in the impoundment increased dramatically following the fish ingress (August in Figs. 23e and 24e). During fall and winter, net fish ingress was low (August through
45
November in Figs. 23b and 24b). In late winter/early spring, water levels receded and fish increased in the deeper creek and perimeter ditch (December through February in
Figs. 23c and 24c) as the marsh drained (December through February in Figs. 23a and
24a). As fish increased in the creek and ditch, piscivorous bird abundance increased once again, although less than the increase following the initial fish ingress (January through
February in Figs. 23e and 24e). Fish increase in the creek and ditch was followed by a marked egress of fish from the impoundment to the adjacent estuary (beginning in
January in Figs. 23b and 24b). Pronounced peaks in piscivorous fish catch per unit effort
(Figs. 23d and 24d) occurred in July, September, April, and June. During low water levels in December through March piscivorous fish catch per unit effort was low despite the high density of fish in the creek and ditch.
Linear correlations (Pearson’s correlation) among fish standing stock, net fish ingress, piscivorous fish and birds, and average monthly water conditions revealed significant relationships (Pearson’s r values > 0.58 represent alpha < 0.05, and r values >
0.71 represent alpha < 0.01). Complete sets of correlations are given in Appendix B.
Monthly water conditions that significantly correlated were temperature and dissolved oxygen (r = -0.81), and culvert water flow and salinity (r = 0.82). Fish standing stock negatively correlated with temperature (r = -0.70), dissolved oxygen (r = -0.73), and water level (r = -0.58). Piscivorous fish catch per unit effort correlated with temperature (r =
0.57). Net fish ingress did not correlate with monthly water conditions (r < 0.44), nor did bird abundance (r < 0.26). If bird abundance, however, is shifted earlier one month in relation to other variables (bird abundance lags other variables), then bird abundance correlates with net fish ingress (r = 0.77) and water level (r = 0.62).
46
Correlations testing for non-linear relationships (Spearman rank correlation) among fish standing stock, net fish ingress, piscivorous fish and birds, and average monthly water conditions revealed additional relationships (Spearman’s r values > 0.58 represent alpha < 0.05, and r values > 0.71 represent alpha < 0.01). Water level and net fish ingress correlated (r = 0.80). Water level had a stronger correlation than temperature on standing stock of fishes with Spearman’s rank correlation, whereas the reverse occurred with Pearson’s correlation.
Fish Standing Stock
Impoundment Marsh Surface
The fishes collected from the marsh surface by cast net in July and October 2000, and January 2001 were primarily resident species, although one transient species, M. cephalus, was collected (Table 4). Biomass conversion by length-weight relationships gave similar results and is given in Appendix C. Neither resident nor transient fish density (number and biomass) differed significantly by month (p values > 0.2; ANOVA)
(Table 5).
Impoundment Ditch, Creek, and Estuary Shoreline
The most common species caught by cast in the impoundment ditch and creek were resident marsh fishes such as P. latipinna, G. holbrooki, and C. variegatus (Table
6). All dominant species were most abundant during winter months. Along the estuary shoreline, gold spotted killifish Floridichthys carpio, an incidental species, ranked among the most common species in addition to resident saltmarsh fishes (Table 7). M. cephalus, a transient species, ranked among the five to six most common fishes both in the salt
47 marsh and along the shoreline. Other transient species, although less common, included
L. xanthurus, E. saurus, and Strongylura notata.
Resident fish account for 95% of the numerical density for all fishes caught by cast net in the impoundment and 75% of the biomass. In general, resident fish density in the ditch and creek was low during July through November when the marsh was flooded
(Fig. 25). Both ditch and creek fish densities increased dramatically in December through
February when water receded from the marsh surface (Fig. 25). High fish density during spring and summer occurred in the creek, while densities in the ditch remained relatively constant during this period (Fig. 25). Shoreline fish density remained relatively low compared to the ditch and creek throughout the study period (Fig. 25). Numerical fish density in the creek and the ditch (pooling months) were 4.1 and 6.6 fish·m-2 higher, respectively, than along the shoreline (p = 0.009, 0.0006; Tukey’s pairwise comparisons)
(Table 8). Resident fish density by biomass in the creek and the ditch were 5.4 and 3.5 g·m-2 higher than along the shoreline (p = 0.003, 0.01; Tukey’s pairwise comparisons).
The numerical density of transient fishes in the impoundment ditch and creek increased steadily throughout the study period, with low abundances occurring during fall through winter, and higher abundances occurring during spring and summer (Fig. 26a).
The density of transient fishes by biomass, however, was more like the pattern shown by resident fishes with the highest density occurring in January (Fig. 26b). Transient fish densities were consistently lower along the estuary shoreline than in the impoundment ditch and creek throughout the year (Fig. 26). Transient fish densities in the creek and ditch (pooling months) were 0.2 and 0.3 fish·m-2 higher, respectively, than along the shoreline (p = 0.02, 0.005; Tukey’s pairwise comparisons) (Table 8). For biomass,
48
transient fish density in the ditch was 0.6 g·m-2 higher than the creek (p = 0.02) and 0.7
g·m-2 higher than the shoreline (p < 0.0001; Tukey’s pairwise comparisons). Transient
fish density (g·m-2) in the creek was not significantly different from the estuary shoreline
(p = 0.08; Tukey’s pairwise comparisons).
Size Distribution of Fishes within the Salt Marsh
Dominant fishes on the marsh surface, C. variegatus and P. latipinna, displayed the same size distribution in October as those caught when the marsh first flooded in July
(Figs. 27 and 28, respectively). As water levels receded in December, C. variegatus left in the remaining ponds on the marsh were 10 mm total length smaller than those present when the marsh was completely flooded (Fig. 27), and P. latipinna were 20 mm total length smaller (Fig. 28).
Fishes commonly collected from the impoundment creek and ditch grew during the study period. Sizes of common impoundment fishes, except M. cephalus, were evenly distributed during July through November, smallest during December through
February, and were highly skewed towards larger fish during June and July (Figs. 29 through 32). Sizes of M. cephalus were smallest during March through May and got progressively larger, with the largest occurring during December through February (Fig.
33). Size frequency distributions for L. parva were evenly distributed throughout the study (Fig. 34).
Fish Ingress/Egress
The comparison of fish passage between adjacent culverts (one culvert with a
reduced flow relative to the other) (Table 9), found no significant differences in total fish
catch numerically (p = 0.20; Kruskal-Wallis One-Way ANOVA) or by biomass (p = 0.14;
49
Kruskal-Wallis One-Way ANOVA) (n = 14 pairs). In the culvert trap fish-retention experiment, 353 fish (264 P. latipinna and 83 C. variegatus, four M. cephalus, two L. parva) were fin-clipped and released into the culvert traps. Of these, 90 (62 P. latipinna,
28 C. variegatus, and zero M. cephalus and L. parva) were recaptured, resulting in a trap retention efficiency of 25%.
Small (< 150 mm total length), numerically dominant fishes (< 150 mm total length) caught in culvert traps were resident species such as C. variegatus, P. latipinna,
M. peninsulae, Palaemonetes pugio, L. parva, and G. holbrooki (Tables 10 and 11). The culvert trap collections included a greater number of species than those from the cast net.
Many of these species were incidental with respect to use of marshes as primary habitat, but some small transient species were caught also. These include important resource species such as red drum S. ocellatus and C. nebulosus.
Resident fish account for 97% of all fishes caught by culvert trap in the salt marsh and 80% of the biomass. During the first half of the study, net ingress occurred, and during the latter half, the reverse occurred (Fig. 35). Over the course of the study, 6% more fish entered the impoundment then left, but over 200% more fish biomass left than entered. Number and biomass of fish that entered and left were roughly similar for P. latipinna, M. peninsulae, G. holbrooki, and L. parva (Table 12). For P. pugio, however, more entered than left, and for C. variegatus and killifish Fundulus spp. more left than entered. For example, 2.5 times as many, and 4.2 times the biomass, of C. variegatus left the impoundment then entered. For Fundulus grandis, 3.7 times as many, and 8.5 times the biomass, left than entered.
50
Differences in resident culvert trap catch per unit effort among locations varied
considerably over time (Fig. 36). Net resident fish ingress at culverts 1 and 3 (pooling
months) differed by 5.1 fish·culvert-1·hr-1 (p = 0.0012; Wilcoxon Signed Ranks Test)
(Table 13). By biomass, net egress at culverts 1 and 4 were at least 3.9 g fish· culvert-1·hr-1 greater than those at culverts 2 and 3 (p values < 0.012; Wilcoxon Signed
Ranks Test). Culvert 4 is located at the southwestern end of the impoundment and
culvert 1 is located at the eastern end of the impoundment at the mouth of the creek (Fig.
10). Resident fish catch (numerical and biomass) among other culvert locations was not
significantly different (p values > 0.10; Wilcoxon Signed Ranks Test).
Direction of net transient fish biomass catch per unit effort throughout most of the
study was from the salt marsh to the estuary (egress), and the magnitude was greatest
during both high water levels in October, and low water levels in December (Fig. 37).
Some numerical net migration into the salt marsh occurred during summer (Fig. 37).
Differences in transient culvert trap catch per unit effort among locations varied
considerably over time (Fig. 38). Net transient fish catch in culvert traps (pooling
months) was not significantly different among culvert locations numerically (p = 0.7;
Kruskal-Wallis One-Way ANOVA) or by biomass (p = 0.3; Kruskal-Wallis One-Way
ANOVA ) (Table 13). Large piscivorous fish (> 150 mm total length) such as E. saurus,
S. ocellatus, and C. nebulosus were captured in culverts (Table 14).
Piscivorous Fishes
Piscivorous transients (i.e., S. ocellatus, E. saurus, and C. nebulosus) were present
in impoundment gill nets primarily during fall months, and L. platyrhincus were most
abundant during April and June (Table 15), coinciding with periods of low salinity. More
51
species were captured along the estuary shoreline than within the impoundment, and the
dominant fishes along the estuary shoreline were nonpiscivorous (i.e., M. cephalus and
Arius felis) (Table 16).
Piscivorous fish catch per unit effort was high both in the creek and ditch during
September, April, and June (Fig. 39). Numerical piscivorous fish catch per unit effort in the ditch was 1.2 fish higher than along the shoreline (p = 0.0009; Wilcoxon Signed
Ranks Test), but was not significantly different among other habitats (p values > 0.29;
Wilcoxon Signed Ranks Test) (Table 17). Piscivorous fish catch per unit effort by biomass was not significantly different among habitats (p = 0.06; Kruskal-Wallis One-
Way ANOVA). Piscivorous fishes thought to use salt marshes as nurseries (S. ocellatus,
E. saurus, L. xanthurus, and C. nebulosus) were more abundant within the impoundment
as large juveniles and small adults than they were as smaller juveniles (< 150 mm total
length) (Figs. 40 through 43).
During a test of culvert trap retention efficiency, 210 piscivorous fish caught in
impoundment gill nets and 67 piscivorous fish caught in shoreline gill nets were fin-
clipped and released. Despite a high number of marked fish, particularly in the
impoundment, only four L. platyrhincus and one C. nebulosus were recaptured. The four
L. platyrhincus were both marked and recaptured within the impoundment, and the C.
nebulosus was marked in the impoundment and recaptured along the estuary shoreline.
Twenty-one percent and 41% of piscivorous fishes caught in the impoundment and
shoreline gill nets, respectively, died. Many of the stomachs of fish that died in gill nets
were empty (Table 18). Of the impoundment-captured fish that had full stomachs, shrimp
(Alpheus heterochaelis and P. pugio) occurred most frequently followed by various
52
species of fish. Benthic invertebrates, crabs, and various fish occurred frequently in
stomachs of shoreline-captured fish.
Piscivorous Birds
Snowy egrets Egretta thula, the most common species in the impoundment (Table
19), were absent from the estuary shoreline (Table 20). Nonpiscivorous birds were
abundant in the impoundment relative to the estuary shoreline, including ibis, waterfowl,
and shorebirds. Butorides striatus, Ardea herodias, Magaceryle alcyon, Anhinga anhinga, and Phalacrocorax auritus were more abundant along the impoundment creek and ditches (not present on the marsh surface) than along the estuary shoreline. An aggregation of over 250 birds (most of which were E. thula; Table 19) was present within
the impoundment upon our arrival in August and persisted for an additional four days
before dispersing. The August bird aggregation occurred on the marsh surface, and the
high bird abundance in January occurred in the creek and along the ditch (Fig. 44).
Piscivorous bird abundance (pooling months) was not significantly different among
habitats either by number (p = 0.09; Kruskal-Wallis One-Way ANOVA), or by biomass
(p = 0.30; Kruskal-Wallis OneWay ANOVA) (Table 21).
Notable Observations
At the onset of marsh flooding during July 2000, schools of P. latipinna, verified by cast net, were observed moving to the east along the Banana Creek shoreline. This species was also the most abundant caught in culvert traps entering the salt marsh during the same period. During January 2001, a widespread fish kill occurred in Banana Creek following a severe freeze. Water temperature dropped below 8 °C during January 1 and remained cold (< 12 °C) for several days. Water temperature again dropped below 12 °C
53
during late January. Dead fish observed along the estuary shoreline adjacent to the
Impoundment C20C included hundreds of A. felis, four Caranx hippos, three M.
atlanticus, and two M. cephalus. A few (between six and twelve) dead P. latipinna were found floating dead in Drainout Creek and the perimeter ditch. Otherwise, resident fishes appeared to have been unaffected. Fish kills were not observed in the marsh at any other time.
A few marsh draining/flooding events occurred during monthly sampling. As the marsh flooded and drained, the level at which the marsh became dry, or became flooded, was noted on the impoundment staff gauge. When flooded, movement of fish onto the marsh surface was observed. As the marsh flooded, fishes appeared to move into the interior of the marsh surface. Highest densities of fish were seen near Distichlis spicata/Juncus spp. boundaries close to uplands. As the marsh drained, fish entered the perimeter ditch. In deeper ponds (> 10 cm deep), small fishes (< 30 mm total length) were present after the shallow marsh surface had drained.
Other animals that were present within the impoundment were Alligator
mississipiensis (one to four were seen during each bird census), Sus scrofa (common),
Procyon lotor (common), Dasypus novemcinctus (common), and one account of Lynx
rufus floridanus. A. mississipiensis was inside culverts on three separate occasions.
Wading birds, especially E. thula, perched on culverts at the opening with the perimeter
ditch and fed on fishes below. Trichechus manatus was observed in the perimeter ditch
during April 2001, after heavy rains and high water levels. It partially lifted itself out of
the water along perimeter ditch bank to reach mangrove branches. During summer and
fall, if water flow from the impoundment through culverts was high (greater than 30
54 cm·s-1), piscivorous fish such as M. atlanticus and Centropomis undecimalis congregated around the culvert outfall plume (usually two to three fish present during high culvert flow out of the salt marsh).
55
Table 4. Fish (no.) captured by cast net on the marsh surface (n = 14 deployments each month).
2000 - 2001
Species Jul Oct Jan Total
Cyprinodon variegatus R 44 64 233 341 Poecilia latipinna R 38 105 15 158 Mugil cephalus T212 23 Lucania parva R527 Gambusia holbrooki R123 6 Fundulus grandis R4 4 Menidia peninsulae R4 4 Fundulus confluentus R33 0 Residents - R 83 184 256 523 Transients - T 21 2 23 Total 104 186 256 546
56
Table 5. Fish Density (fish·m-2 and g·fish·m-2) on the marsh surface.
Number (2000 - 2001) Biomass (2000 - 2001)
Month Jul Oct Jan Jul Oct Jan
Residents: Average 2.1 4.7 6.5 3.4 8.5 3.7 SE 1.2 3.1 3.0 0.9 2.3 1.0
Transients: Average 0.5 0.1 4.7 0.7 SE 0.5 0.1 4.7 0.7
Total: Average 2.7 4.7 6.5 8.1 9.2 3.7 SE 1.2 3.1 3.0 4.8 5.0 2.0
Table 6. Fish (no.) captured by cast net within ditch and creek in Impoundment C20C (n = 28 deployments each month).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Total
Poecilia latipinna R 2 51 5 1 2 245 1,277 322 79 122 579 28 605 3,318 Gambusia holbrooki R 3 5 452 913 89 77 24 11 4 5 1,583 Cyprinodon variegatus R 4 2 1 3 218 436 300 56 150 121 73 178 1,542 Mugil cephalus T 11 6 2 1333385420419728343 Menidia peninsulae R 1 4 10 66 13 7 20 10 2 8 14 155 Lucania parva R 1 126601932 1 6119 Palaemonetes pugio R 5 3 12 8 26 20 2 9 85 Fundulus grandis R 1 15814519650 Fundulus confluentus R 3 731121422 57 Anchoa mitchilli I 2 524 13 Leiostomus xanthurus T4 2 1 2 9 Elops saurus T3 36 Strongylura notata T1 1 13 Jordanella floridae R 11 Microgobius gulosus I1 1
Residents - R 3 65 7 6 24 1,037 2,722 767 240 335 719 123 827 6,875 Transients - T 8 14 0 6 3 13 33 38 54 20 41 102 29 361 Incidentals - I 0 0 0 0 2 1 5 0 2 0 4 0 0 14 Total 11 79 7 12 29 1,051 2,760 805 296 355 764 225 856 7,250
Table 7. Fish (no.) captured by cast net along Banana Creek shoreline adjacent to Impoundment C20C (n = 14 deployments each month).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Total
Poecilia latipinna 15 23 5 48 2 91 75 259 Cyprinodon variegatus 7 1 18 8 2 60 7 5 43 77 228 Floridichthys carpio 14 36 4 1 6 8 20 30 119 Palaemonetes pugio 1 2222204417687 Lucania parva 5811 7 1411210316785 Mugil cephalus 43 13 1143 41236 Gambusia holbrooki 24 1 1 1 27 Anchoa mitchilli 335 11 58 Sygnathus scovelli 33 12 9 Menidia peninsulae 44 8 Fundulus grandis 1 56 Brevoortia smithi 4 4 Microgobius gulosus 111 3 Elops saurus 1 1 Cynoscion nebulosus 1 1 Eucinostomus argenteus 11 Gobiosoma bosc 11 Gobiosoma robustum 1 1 Hippocampus reidi 11
Total 51 71 9 8 7 56 47 25 116 79 25 186 208 888
Table 8. Comparison of fish density (no. fish·m-2 and g fish·m-2) among saltmarsh habitats and estuary shoreline. Values are means of each habitat (pooling months) for the study period, (n = 182 cast net deployments for each habitat).
Number Biomass
Habitat Creek Ditch Shoreline Creek Ditch Shoreline
Residents: Average 5.5 8.0 1.4 7.4 5.5 2.0 SE 1.1 2.8 0.2 1.6 1.2 0.5 Statistical group A A B A A B
Transients: Average 0.3 0.4 0.1 1.1 3.2 0.4 SE 0.1 0.1 0.03 0.3 0.9 0.2 Statistical group A A B B A B 59
Table 9. Comparison of fish catch (no. and g fish·trap-1·hr-1) between reduced flow and unmodified culvert traps. Values shown are means for each trap type (n = 167 hrs fished for each trap type).
Number Biomass
Habitat Unmodified Trap Reduced Flow Trap Unmodified Trap Reduced Flow Trap
Average -1.5 -4.2 -1.0 1.2 SE 1.5 3.1 4.2 5.0 Statistical group A A A A 60
Table 10. Number of small fish (< 150 mm total length) moving out of Impoundment C20C captured by culvert trap.
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs traps fished) (369) (369) (367) (346) (378) (357) (363) (195) (359) (283) (369) (370) (4,124)
Cyprinodon variegatus R 253 250 6 1 24 4,145 1,682 88 160 94 2,089 8,792 Poecilia latipinna R 2,986 2,341 51 119 3 62 721 233 352 467 383 550 8,268 Menidia peninsulae R 87 10 9 240 2 293 384 269 1,530 151 375 182 3,532 Palaemonetes pugio R 94 187 148 328 59 104 529 270 267 120 248 598 2,952 Lucania parva T 232 145 45 135 73 564 113 236 16 43 109 1,711 Gambusia holbrooki R 175 64 10 77 1 25 69 41 104 47 131 96 840 Mugil cephalus T 2 29 4 163 84 79 67 15 5 30 478 Fundulus grandis R 6 3 2 219 3 3 1 1 238 61 Leiostomus xanthurus T 16 12 5 106 2 4 16 2 12 175 Alpheus heterochaelis I 12 3 3 1 3 7 34 63 Anchoa mitchilli I 3 281831 35 Trinectes maculatus T 2 24 3 1 30 Microgobius gulosus I1 413 1 11030 Gobiosoma robustum I 12 64345530 Gobiosoma bosc I 1 1 111223223 Cynoscion nebulosus T 741 12 Fundulus confluentus R5 2 2 1 1 11 Strongylura notata T1 6 7 Floridichthys carpio I1 2 1 2 1 7 Eucinostomus argenteus I12 3 Elops saurus T1 1 2 Callinectes sapidus T112 Sygnathus scovelli I1 1
Table 10. Continued
Penaeus aztecus I1 1 Malaclemys terrapin tequesta R1 1 Lepomis macrochirus I1 1 Jordanella floridae R11 Hippocampus reidi I1 1 Hippocampus erectus I11 Arius felis I1 1
Residents - R 3,607 2,857 224 765 65 512 6,068 2,499 2,344 946 1,231 3,517 24,635 Transients - T 250 168 107 252 4 239 649 192 307 47 51 151 2,417 Incidentals - I 15 2 8 19 3 9 21 18 31 9 10 52 197 Total 3,872 3,027 339 1,036 72 760 6,738 2,709 2,682 1,002 1,292 3,720 27,249 62
Table 11. Number of small fish (< 150 mm total length) moving into Impoundment C20C captured by culvert trap.
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs traps fished) (369) (369) (367) (346) (378) (357) (363) (195) (359) (283) (369) (370) (4,124)
Poecilia latipinna R 7,518 2,437 57 84 5 34 450 82 93 224 56 346 11,386 Palaemonetes pugio R 168 297 281 765 88 151 992 487 451 360 258 1,701 5,999 Cyprinodon variegatus R 1,216 168 6 30 65 737 822 87 64 91 270 3,556 Menidia peninsulae R 318 39 39 283 4 543 612 144 707 101 221 129 3,140 Lucania parva R 645 280 52 128 14 228 940 178 331 35 45 103 2,979 Gambusia holbrooki R 457 162 13 75 33 99 44 92 63 122 75 1,235 Mugil cephalus T 30 5 1 40 7 66 37 39 6 57 288 Fundulus grandis R3047512 522 6 64 63 Gobiosoma robustum I 2 26 336841347 Strongylura notata T33 1 3 37 Gobiosoma bosc I 1 3 82654231 Alpheus heterochaelis I28244323 Trinectes maculatus T2 2101 1 1 3 20 Microgobius gulosus I 4711 1 519 Anchoa mitchilli I212712 Leiostomus xanthurus T1 6 2 9 Fundulus confluentus R311 11 1 8 Floridichthys carpio I3 1 2 1 7 Eucinostomus argenteus I134 Cynoscion nebulosus T4 4 Sciaenops ocellatus T123 Sygnathus scovelli I1 1 Jordanella floridae R11
Table 11. Continued
Hippocampus erectus I11 Chilomycterus schoepfi I1 1 Chasmodes bosquianus I1 1
Residents - R 10,355 3,388 456 1,370 112 1,056 3,837 1,760 1,763 847 800 2,624 28,368 Transients - T 36 6 40 6 2 40 8 67 45 41 7 63 361 Incidentals - I 5 2 8 17 7 14 16 5 24 18 8 23 147 Total 10,396 3,396 504 1,393 121 1,110 3,861 1,832 1,832 906 815 2,710 28,876 64
Table 12. Net egress of resident saltmarsh fish (no. and g fish) from Impoundment C20C over the entire study period (n = 4,124 hrs traps fished).
Number Biomass
Net Fish Egress Egress / Net Fish Egress Egress / Species Egress Ingress (egress - ingress) Ingress Egress Ingress (egress - ingress) Ingress (no.) (no.) (no.) (g) (g) (g)
Cyprinodon variegatus 8,792 3,556 5,236 2.47 19,998 4,711 -15,287 4.25 Fundulus grandis 238 64 174 3.72 3,902 459 -3,443 8.51 Menidia peninsulae 3,532 3,140 392 1.12 5,393 3,662 -1,731 1.47 Fundulus confluentus 11 8 3 1.38 39 15 -23 2.53 Gambusia holbrooki 840 1,235 -395 0.68 351 525 173 0.67 65 Palaemonetes pugio 2,952 5,999 -3,047 0.49 871 1,761 890 0.49 Lucania parva 1,711 2,979 -1,268 0.57 2,018 3,105 1,087 0.65 Poecilia latipinna 8,268 11,386 -3,118 0.73 9,636 11,234 1,598 0.86 Other Fish 905 509 396 1.78 15,029 2,217 -12,812 6.78
Total 27,249 28,876 -1,627 0.94 57,236 27,687 -16,737 2.07
Table 13. Comparison of net fish ingress (no. and g fish·culvert-1·hr-1) among culvert locations. Values are means of each habitat (pooling months) for the study period; negative values indicate net egress.
Number Biomass
Culvert Location 1 2 3 4 1 2 3 4 N (hrs traps fished) (1,079) (991) (1,074) (980) (1,079) (991) (1,074) (980)
Residents: Average -1.8 1.6 3.3 1.0 -9.7 0.4 1.5 -3.5 SE 2.2 0.7 0.8 0.7 3.9 1.1 1.1 2.3 Statistical group A A A A B B A BBB 66 Transients: Average -0.1 0.1 -0.2 -0.04 -3.0 -0.3 -3.0 -1.4 SE 0.1 0.1 0.1 0.03 2.1 0.5 1.4 0.5 Statistical group A A A A A A A A
Table 14. Number of large fish (> 150 mm total length) moving in and out of Impoundment C20C captured by culvert trap.
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs traps fished) (369) (369) (367) (346) (378) (357) (363) (195) (359) (283) (369) (370) (4,124)
Egress
Mugil cephalus T1232681266571521144229 Leiostomus xanthurus T 282143296 3 193 Elops saurus T222226115 2 88 Strongylura notata T3171 12 Sciaenops ocellatus T11 68 67 Cynoscion nebulosus T121 4 Lepisosteus platyrhincus R22 Dasiatus sabina I1 1
Ingress
Mugil cephalus T9531119 Elops saurus T2 1 3 Strongylura notata T3 3
Table 15. Fish (no.) captured by gill net within Impoundment C20C. Piscivorous fishes indicated by asterisk (R = residents, T = transients, I = Incidentals).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs 10 m nets fished) (14) (24) (21) (11) (10) (13) (12) (14) (13) (13) (12) (13) (169)
Lepisosteus platyrhincus* R 3 40 6 3 9 7 6 30 4 59 167 Mugil cephalus T12431633 2 43 Sciaenops ocellatus* T8 8 20 2 1 1 40 Cynoscion nebulosus* T9552 1 741 34 Elops saurus* T88511 124 Leiostomus xanthurus T4 221 1 515 68 Arius felis I11
Piscivorous 25 24 70 9 4 12 7 7 7 34 6 60 265 Non-piscivorous 16 4 5 18 4 3 1 3 5 59 Total 412875278 157 8 7 376 65324
Table 16. Fish (no.) captured by gill net along Banana Creek shoreline adjacent to Impoundment C20C. Piscivorous fishes indicated by asterisk (R = residents, T = transients, I = Incidentals).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs 10 m nets fished) (14) (24) (21) (11) (10) (13) (12) (14) (13) (13) (12) (13) (169)
Arius felis 8 57 24 16 6 8 1 9 6 10 13 158 Mugil cephalus 1922772 13 131470 Sciaenops ocellatus* 85525 1 13 30 Elops saurus* 135441 128 Dasyatis sabina 152 6216 Cynoscion nebulosus* 3141 1111 69 Caranx hippos* 151 11 9 Leiostomus xanthurus 2221 1 8 Lepisosteus platyrhincus* 222 1 7 Megalops atlanticus* 12 3 Centropomis undecimalis* 112 Diapterus auratus 22 Pogonias cromis* 11 2 Bairdiella chrysoura 11 Dorosoma cepedianum 11 Micropogonias undulatus 11 Sphoeroides nephelus 11
Piscivorous 1615132466 11135192 Non-piscivorous 9 68 47 32 19 12 2 3 10 7 20 29 258 Total 2583605625183 4 11102530350
Table 17. Comparison of piscivorous and nonpiscivorous fish catch (no. and g fish·10 m net-1·hr-1) among saltmarsh habitats and estuary shoreline. Values are means of each habitat (pooling months) for the study period.
Number Biomass
Habitat Creek Ditch Shoreline Creek Ditch Shoreline N (hrs 10 m net fished) (89) (80) (173) (89) (80) (173)
Piscivorous Average 1.2 1.8 0.5 728.5 998.3 341.8 Fish SE 0.4 0.3 0.1 253.0 205.4 76.1 Statistical group A A A A A BB 70 NonPiscivorous Average 0.3 0.5 1.5 121.2 123.2 820.7 Fish SE 0.2 0.1 0.3 62.4 38.1 221.7 Statistical groupAABAAB
Table 18. Stomach contents of piscivorous fish caught in gill nets.
Frequency of occurrence (no.)
Species N Empty Misc. Alpheus Grass Gobies Gambusia Poecilia Menidia Cyprinodon Benthic Crabs Arius Lucania Fish Shrimp Inverts
Impoundment
Sciaenops ocellatus 19 9 2 4 3 1 1 Cynoscion nebulosus 11 10 1 1 Elops saurus 21 7 8 1 1 2 2 1 Lepisosteus - 43 1 platyrhincus 71 Total 55 29 12 4 4 2 2 2 2 1
Shoreline
Sciaenops ocellatus 13 6 2 1 1 4 Elops saurus 22 7 3 2 4 5 2 1
Total 35 13 5 1 2 5 5 4 2 1
Table 19. Birds (no.) present within Impoundment C20C during monthly counts (n = 2 counts each month). Piscivorous birds denoted by asterisk.
2000 2001
Species Common Name Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Egretta thula* snowy egret 1 189 2 7 32 2 233 Eudocimus albus white ibis 4 9 91 3 25 2 2 3 4 143 Plegadis falcinellus glossy ibis 49 9 54 112 Hydranassa tricolor* Louisiana heron 8 48 2 3 11 10 3 4 1 3 3 96 waterfowl 1 10 3 42 5 24 2 87 Casmerodius albus* great egret 6405712 124 1 78 shorebirds 14 18 32
Mycteria americana* wood stork 6 16 3 3 28 72 Ajaia ajaja roseate spoonbill 10 12 1 2 25 Butorides striatus* green heron 4 6 2 1 1 2 3 4 23 Ardea herodias* great blue heron 32153 121 321 Megaceryle alcyon* belted kingfisher 2 1 3 2 3 2 1 14 Anhinga anhinga* American anhinga 1 1 4 2 1 2 1 1 13 Dichromanassa rufescens* reddish egret 1 9 10 Himantopus mexicanus black-necked stilt 4 6 10 Nycticorax nycticorax* blk.-crowned night heron 4 4 Phalacrocorax auritus* dbl.-crested cormorant 1 1 1 3 Florida caerulea* little blue heron 1 1 2 Pelecanus occidentalis* brown pelican 1 1
Piscivorous Birds 31 297 16 40 16 19 62 16 5 6 8 10 526 Non-Piscivorous Birds 14 21 1 151 15 135 25 24 4 2 13 4 409 Total 45 318 17 191 31 154 87 40 9 8 21 14 935
Table 20. Birds (no.) present along Banana Creek shoreline adjacent to Impoundment C20C during monthly counts (n = 2 counts each month). Piscivorous birds denoted by asterisk.
2000 2001
Species Common Name Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total
Ardea herodias* great blue heron 2 2 2 8 1 3 1 19 Eudocimus albus white ibis 7 7 14 Hydranassa tricolor* Louisiana heron 2 2 3 1 8 Mycteria americana* wood stork 1 7 8 Casmerodius albus* great egret 3 2 2 7 Phalacrocorax auritus* double-crested cormorant 1 6 7 Pelecanus erythrorhynchos* white pelican 4 4 73 Pelecanus occidentalis* brown pelican 3 3 Anhinga anhinga* American anhinga 2 2 Butorides striatus* green heron 1 1 2 Pandion haliaetus* osprey 11
Piscivorous Birds 8 4 1 2 6 33 1 5 1 61 Non-Piscivorous Birds 7 7 14 Total 154 126 3385 175
Table 21. Comparison of bird abundance (no. and g) among saltmarsh habitats and estuary shoreline. Values are means of each habitat (pooling months) for the study period (n = 24 bird counts for each habitat).
Number Biomass
Habitat Creek Ditch Marsh Shoreline Creek Ditch Marsh Shoreline
Average 2.4 4.0 15.5 2.5 1,986 2,465 10,809 5,207 SE 2.3 3.5 38.2 2.1 2,134 1,789 18,442 5,143 Statistical groupAAAAAAAA 74
Banana Creek Impoundment C20C 1 Marsh Elevation
0.9 Study Period
0.8
0.7
0.6
0.5
0.4 75 Water Level (m)
0.3
0.2
0.1
0
3-Jul-01 18-Jul-00 9-Jan-017-Feb-018-Mar-016-Apr-015-May-013-Jun-01 29-Oct-9927-Nov-9926-Dec-9925-Jan-0023-Feb-0023-Mar-0021-Apr-0020-May-0018-Jun-00 16-Aug-0014-Sep-0013-Oct-0011-Nov-0010-Dec-00 Date
Fig. 12. Water level during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek.
40 Study Period
35
30
25
20 76
Temperature (°C) 15
10
Banana Creek 5 Impoundment C20C.
0
3-Jul-01 18-Jul-00 9-Jan-017-Feb-018-Mar-016-Apr-015-May-013-Jun-01 29-Oct-9927-Nov-9926-Dec-9925-Jan-0023-Feb-0023-Mar-0021-Apr-0020-May-0018-Jun-00 16-Aug-0014-Sep-0013-Oct-0011-Nov-0010-Dec-00 Date
Fig. 13. Water temperature during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek.
Summer 2000
40
35
30
25 Banana Creek Impoundment C20C. 20 77
Temperature (°C) 15
10
5
0 5-Jul-00 6-Jul-00 7-Jul-00 8-Jul-00 9-Jul-00 10-Jul-00 11-Jul-00 12-Jul-00 13-Jul-00 14-Jul-00 15-Jul-00 Date
Fig. 14. Diurnal changes in temperature during a typical 10-day period.
50 Study Period 45
40
35
30
25 Salinity (‰) 20 78
15
10 Banana Creek 5 Impoundment C20C
0
3-Jul-01 18-Jul-00 9-Jan-017-Feb-018-Mar-016-Apr-015-May-013-Jun-01 29-Oct-9927-Nov-9926-Dec-9925-Jan-0023-Feb-0023-Mar-0021-Apr-0020-May-0018-Jun-00 16-Aug-0014-Sep-0013-Oct-0011-Nov-0010-Dec-00 Date
Fig. 15. Salinity during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek.
Banana Creek 20 Impoundment C20C
18 Study Period 16
) 14 -1
12
10 79 8
Dissolved Oxygen (mg L 6
4
2
0
3-Jul-01 18-Jul-00 9-Jan-017-Feb-018-Mar-016-Apr-015-May-013-Jun-01 29-Oct-9927-Nov-9926-Dec-9925-Jan-0023-Feb-0023-Mar-0021-Apr-0020-May-0018-Jun-00 16-Aug-0014-Sep-0013-Oct-0011-Nov-0010-Dec-00 Date
Fig. 16. Dissolved oxygen during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek.
Banana Creek Impoundment C20C
800 Study Period
600
400
200 80
Redox Potential (mV) 0
-200
-400
3-Jul-01 18-Jul-00 9-Jan-017-Feb-018-Mar-016-Apr-015-May-013-Jun-01 29-Oct-9927-Nov-9926-Dec-9925-Jan-0023-Feb-0023-Mar-0021-Apr-0020-May-0018-Jun-00 16-Aug-0014-Sep-0013-Oct-0011-Nov-0010-Dec-00 Date
Fig. 17. Redox potential during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek.
Summer 2000
9 Banana Creek
8 Impoundment C20C
7
) 6 -1
5 81
4
Dissolved Oxygen (mg·L 3
2
1
0 5-Jul-00 6-Jul-00 7-Jul-00 8-Jul-00 9-Jul-00 10-Jul-00 11-Jul-00 12-Jul-00 13-Jul-00 14-Jul-00 15-Jul-00 Date
Fig. 18. Diurnal changes in dissolved oxygen during a typical 10-day period.
Summer 2000
600 Banana Creek Impoundment C20C 500
400
300
200 82
100 Redox Potential (mV)
0
-100
-200 5-Jul-00 6-Jul-00 7-Jul-00 8-Jul-00 9-Jul-00 10-Jul-00 11-Jul-00 12-Jul-00 13-Jul-00 14-Jul-00 15-Jul-00 Date
Fig. 19. Diurnal changes in redox potential during a typical 10-day period.
12 Study Period
10
8
6 pH Banana Creek Impoundment C20C 83
4
2
0
3-Jul-01 18-Jul-00 9-Jan-017-Feb-018-Mar-016-Apr-015-May-013-Jun-01 29-Oct-9927-Nov-9926-Dec-9925-Jan-0023-Feb-0023-Mar-0021-Apr-0020-May-0018-Jun-00 16-Aug-0014-Sep-0013-Oct-0011-Nov-0010-Dec-00 Date
Fig. 20. pH during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek.
Summer 2000
9.4
9.2
9
8.8
8.6
8.4 84 pH
8.2
Banana Creek 8 Impoundment C20C
7.8
7.6
7.4 5-Jul-00 6-Jul-00 7-Jul-00 8-Jul-00 9-Jul-00 10-Jul-00 11-Jul-00 12-Jul-00 13-Jul-00 14-Jul-00 15-Jul-00 Date
Fig. 21. Diurnal changes in pH during a typical 10-day period.
60
50 Culvert 1 40 Culvert 2
) Culvert 3 -1 30 Culvert 4
20
10
0
-10 85
-20 Water Flow through Culverts (cm·s Culverts through Flow Water -30
-40
-50 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 22. Average monthly water flow through Impoundment C20C culverts during study period. Water flow was measured prior to each culvert trap deployment.
86
1 a 0.8 0.6 0.4 0.2
Water Level (m)Water Level 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 25 -1 20 b ·Hr
-1 15 10 5 0 -5 -10
Net No. Fish·Culvert -15
60 c 50 -2 40 30 20 No. Fish·m No. 10 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun July
6 d 5 -1
·Hr 4 -1 3 2
10m Net 1 No. Pisciv. Fish· Fish· Pisciv. No. 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
300
250 e 200 150 100
No. Pisciv. Birds 50 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 23. Average water level (a), and numbers involved in net fish migration (b), fish standing stock (c), piscivorous fish catch per unit effort (d), and piscivorous bird abundance (e). Error bars represent standard error.
87
1 a 0.8 0.6 0.4 0.2
W ater Level (m) 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 25
-1 15 b ·Hr
-1 5 -5 -15 -25 -35 Net g Fish·Culvert g Net -45
35 c 30 25 -2 20 15
g Fish·m 10 5 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun July
5000 d
-1 4000 ·Hr
-1 3000 2000
1000 g Pisciv. Fish· Fish· Pisciv. g 10m Net 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
120000 e
80000
40000 g Pisciv. Birds Birds Pisciv. g
0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 24. Average water level (a), and biomass involved in net fish migration (b), fish standing stock (c), piscivorous fish catch per unit effort (d), and piscivorous bird abundance (e). Error bars represent standard error.
Standing Stock by Habitat - Resident Fish 100 a 90 )
-2 80 Ditch 70 Creek 60 Shoreline 50 40 30 20 Fish density (no.·m 10 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun July
b 45
40 88
) 35 -2 30 Ditch 25 Creek 20 Shoreline 15
Fish density (g·m density Fish 10 5 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun July Month (2000 - 2001)
Fig. 25. Number (a) and biomass (b) of the standing stock of resident fishes by habitat. Error bars represent standard error.
3 Standing Stock by Habitat - Transient Fish a
2.5 )
-2 Ditch 2 Creek Shoreline 1.5
1
Fish density (no.·m 0.5
0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun July
25 89
b 20 Ditch ) -2 Creek 15 Shoreline
10
Fish density (g·m 5
0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun July Month (2000 - 2001)
Fig. 26. Number (a) and biomass (b) of the standing stock of transient fishes by habitat. Error bars represent standard error.
Cyprinodon variegatus - Marsh Surface
0.3
0.2
Jul Oct 90 Jan Relative Frequency (%) 0.1
0 9-10 11-12 13-14 15-16 17-18 19-20 21-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42 43-44 45-46 47-48 49-50 51-52 53-54 55-56 57-58
Total Length (mm)
Fig. 27. Size (mm total length) frequency of Cyprinodon variegatus caught by cast net on the marsh surface at Impoundment C20C.
Poecilia latipinna - Marsh Surface
0.3
0.2
Jul Oct
Jan 91 Relative Frequency (%) 0.1
0 9-10 11-12 13-14 15-16 17-18 19-20 21-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42 43-44 45-46 47-48 49-50 51-52 53-54 55-56
Total Length (mm)
Fig. 28. Size (mm total length) frequency of Poecilia latipinna caught by cast net on the marsh surface at Impoundment C20C.
Poecilia latipinna - Ditch and Creek
0.3
Jul-Nov 0.2 Dec-Feb Mar-May Jun-Jul 92
Relative Frequency (%) 0.1
0 9-10 11-12 13-14 15-16 17-18 19-20 21-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42 43-44 45-46 47-48 49-50 51-52 53-54 55-56 57-58 59-60 61-62 63-64 65-66 67-68 69-70
Total Length (mm)
Fig. 29. Size (mm total length) frequency of Poecilia latipinna caught by cast net in ditch and creek within Impoundment C20C.
Gambusia holbrooki - Ditch and Creek
0.3
Jul-Nov Dec-Feb Mar-May 0.2 Jun-Jul 93
Relative Frequency (%) 0.1
0 9-10 11-12 13-14 15-16 17-18 19-20 21-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42
Total Length (mm)
Fig. 30. Size (mm total length) frequency of Gambusia holbrooki caught by cast net in ditch and creek within Impoundment C20C.
Cyprinodon variegatus - Ditch and Creek
0.3
0.2 Jul-Nov Dec-Feb Mar-May Jun-Jul 94
Relative Frequency (%) 0.1
0 15-16 17-18 19-20 21-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42 43-44 45-46 47-48 49-50 51-52 53-54 55-56 57-58 59-60 61-62 63-64
Total Length (mm)
Fig. 31. Size (mm total length) frequency of Cyprinodon variegatus caught by cast net in ditch and creek within Impoundment C20C.
Menidia peninsulae - Ditch and Creek
0.4
0.3
Jul-Nov Dec-Feb Mar-May 0.2 Jun-July 95 Relative Frequency (%)
0.1
0 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60 61-65 66-70 71-75 76-80 81-85 86-90 91-95 96-100
Total Length (mm)
Fig. 32. Size (mm total length) frequency of Menidia peninsulae caught by cast net in ditch and creek within Impoundment C20C.
Mugil cephalus - Ditch and Creek 0.4
0.3
Jul-Nov Dec-Feb 0.2 Mar-May Jun -Jul 96 Relative Frequency (%)
0.1
0 0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100 101-110 111-120 121-130 131-140 141-150 151-160 161-170 171-180 181-190 191-200 201-210 211-220 221-230 231-240 241-250 251-260 261-270 271-280 281-290 291-300 301-310 311-320 > 321
Total Length (mm)
Fig. 33. Size (mm total length) frequency of Mugil cephalus caught by cast net in ditch and creek within Impoundment C20C.
Lucania parva - Ditch and Creek
0.6
0.5
0.4
Jul-Nov Dec-Feb 0.3 Mar-May Jun-July 97 Relative Frequency (%) 0.2
0.1
0 21-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42
Total Length (mm)
Fig. 34. Size (mm total length) frequency of Lucania parva caught by cast net in ditch and creek within Impoundment C20C.
-1 35 Ingress and Egress of Resident Fish ·Hr
-1 30 a 25 Ingress 20 Egress 15 10 5
No. Resident Fish·Trap Resident No. 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 98 50
-1 45 b
·Hr 40 -1 35 Ingress 30 Egress 25 20 15 10
g Resident Fish·Trap 5 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 35. Catch rate of resident fish, number (a) and biomass (b), in culvert traps during study period.
60 Net Ingress by Culvert Location - Resident Fish Culvert 1 a 50 Culvert 2 Culvert 3 40
-1 Culvert 4 30 ·Hr -1 20 10 0 -10
No. Fish·Culvert No. -20
-30 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun -40 b 60 Culvert 1 Culvert 2 99 40 Culvert 3 Culvert 4 20 -1
·Hr 0 -1
-20
-40
g Fish·Culvert -60
-80 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun -100 Month (2000 - 2001)
Fig. 36. Net resident fish ingress (catch per unit effort), number (a) and biomass (b), by culvert location (negative indicates movement out of impoundment). Error bars represent standard error.
-1 1 Ingress and Egress of Transient Fish ·Hr -1 0.8 Ingress a 0.6 Egress
0.4
0.2
No. Fish·Trap Transient 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
20 100
-1 18
·Hr 16
-1 b 14 Ingress 12 Egress 10 8 6 4 2 g Transient Fish·Trap g Transient 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 37. Catch rate of transient fish, number (a) and biomass (b), in culvert traps during study period.
1.5 Net Ingress by Culvert Location - Transient Fish a 1 -1 0.5 ·Hr -1 0
-0.5 Culvert 1 Culvert 2 -1 Culvert 3 No. Fish·Culvert Culvert 4 -1.5
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun -2
10 b 101
0
-1 -10 ·Hr -1 -20 Culvert 1 -30 Culvert 2 Culvert 3 -40 Culvert 4 g Fish·Culvert
-50 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun -60 Month (2000 - 2001)
Fig. 38. Net transient fish ingress (catch per unit effort), number (a) and biomass (b), by culvert location (negative indicates movement out of impoundment). Error bars represent standard error.
7 Piscivorous Fish by Habitat a 6 Ditch -1
·Hr 5 Creek -1 Shoreline 4
3
2
No. Fish·10m Net Fish·10m No. 1
0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
5000 b 102 4500 4000 Ditch -1 Creek ·Hr 3500 -1 3000 Shoreline 2500 2000 1500
g Fish·10m Net 1000 500 0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 39. Piscivorous fish catch per unit effort in gill nets, number (a) and biomass (b), by habitat. Error bars represent standard error.
Sciaenops ocellatus
16
14
12
10
8 Culvert Trap 103 Frequency (No.) 6 Gill Net
4
2
0 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500
Total Length (mm)
Fig. 40. Size (mm total length) frequency of Sciaenops ocellatus captured by culvert trap and gill net during study period in Impoundment C20C. None were caught by cast net. Approximate age at maturity is 650 mm total length.
Elops saurus
25
20
Cast Net 15 Culvert Trap Gill Net
10 104 Frequency (No.)
5
0 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500
Total Length (mm)
Fig. 41. Size (mm total length) frequency of Elops saurus captured by cast net, culvert trap, and gill net during study period in Impoundment C20C. Approximate age at maturity is about 400 mm total length.
Leiostomus xanthurus
120
100
80 Cast Net Culvert Trap 60 Gill Net 105 Frequency (No.)
40
20
0 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300
Total Length (mm)
Fig. 42. Size (mm total length) frequency of Leiostomus xanthurus captured by cast net, culvert trap, and gill net during study period in Impoundment C20C. Approximate age at maturity is 120 mm total length.
Cynoscion nebulosus
15
10 Culvert Trap Gill Net 106 Frequency (No.)
5
0 26-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500
Total Length (mm)
Fig. 43. Size (mm total length) frequency of Cynoscion nebulosus captured by culvert trap and gill net during study period in Impoundment C20C. None were caught by cast net. Approximate age at maturity is 440 mm total length.
35 Piscivorous Birds by Habitat a
-1 30 143 ± 124 Ditch 25 Creek 20 Marsh Surface Shoreline 15
10
5 No. Pisciv. Birds·Impound Pisciv. No.
0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
60000 b 107
-1 50000 76,000 Ditch 40000 ± 54,000 Creek Marsh Surface 30000 Shoreline 20000
10000 g Pisciv. Birds·Impound
0 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Month (2000 - 2001)
Fig. 44. Number (a) and estimated biomass (b) of piscivorous birds by habitat. Error bars represent standard error.
CHAPTER 4 FIELD DISCUSSION
Water Conditions
Fish kills resulting from low oxygen levels occasionally occur during summer in the northern Indian River Lagoon, particularly in areas sheltered from wind or following several days of cloudiness when respiration exceeds photosynthesis for extended periods
(Jim Egan, Marine Resources Council, pers. comm.). The fishes killed first during this period are those that live close to the bottom (e.g., flounder) where dissolved oxygen and redox potential is lowest and hydrogen sulfide concentrations would be expected to be greatest (Jim Egan, Marine Resources Council, pers. comm.). Despite low dissolved oxygen and redox potential in Banana Creek and Impoundment C20C, particularly during morning hours, fishes were present among impoundment and estuary shoreline habitats.
No dead fish were observed during the study (except freeze-killed fish), even during summer when dissolved oxygen and redox potential reached their lowest minimum levels.
Ditches and small creeks may offer thermal refuge for fishes during cold periods
(Adams and Tremain 1999). During winter, water temperature in Banana Creek was lower than in the impoundment. The ditch is more protected from cold winds than the more exposed Banana Creek, and the surface area to depth ratio is greater in Banana
Creek, allowing cold winds to have a greater influence on water temperature by mixing the water column. Despite potential refuge from low temperatures offered within the
108 109 impoundment, large piscivorous fishes occurred in low abundance during winter contrary to results from a large estuarine creek on Merritt Island connected to the Indian River
Lagoon, where the highest abundances of red drum occurred during winter (Adams and
Tremain 1999).
Resident Fish Hypotheses
Given that saltmarsh fish left the impoundment at over 200% greater biomass than when they entered, the marsh appears to function essentially as a net exporter of forage fish to the adjacent estuary, consistent with Resident Hypothesis 1. As water levels receded, resident marsh fishes concentrated in ditches and creeks, and the youngest residents remained in deeper ponds on the marsh surface, consistent with data for tidal marshes (Kneib 1993). Crowding may have influenced the fish migration to the estuary that ensued. In a Georgia tidal marsh, when the mummichog Fundulus heteroclitus was added to experimental enclosures on the marsh surface at four times normal density for six weeks, one-third to three-fourths of the fish died or escaped (Kneib 1981). Fish at high densities also exhibited reduced growth rates and fecundity (Kneib 1981; Weisberg and Lotrich 1986). Kneib (1981) suggested that F. heteroclitus would not likely sustain densities at the high levels forced in his study, and would normally respond to high density by emigrating. In the present study, density-dependent effects may well have triggered the marked egress of resident marsh fishes from the impoundment. Monthly seining in the Merritt Island area shows an abundance of resident saltmarsh fishes in the estuary (Florida Marine Research Institute, unpubl. data). During spring, when water levels have receded from marshes, L. parva, M. peninsulae, and C. variegatus rank among the top five most abundant species.
110
Resident fish migrations from saltmarsh creeks to the estuary resulting from overcrowding may be unique to seasonally flooded marshes. In tidal systems, marsh residents migrate to creeks during low tide, but probably only occupy this habitat temporarily because access to the marsh surface will occur again only hours later. Thus, resident fishes in such systems face crowded conditions in creeks for only a short period, contrary to seasonally flooded marshes that may remain dry for several months, prompting fish to migrate to the estuary in response to overcrowding. In tidal systems, movement of saltmarsh production to the estuary by residents may be limited only to trophic interactions with larger transient fishes that occur near creek entrances and along creek banks when residents are concentrated there at low tide (Kneib 1997).
An unexpected result during the study was the marked ingress of resident marsh fishes into the impoundment from the estuary at the onset of marsh flooding, which was also the time of observed schooling of P. latipinna along the estuary shoreline. These schooling fish may have been seeking food, spawning habitat, and refuge on the marsh surface as soon as it became available. The low density of fish in the impoundment ditch and creek, and their presence on the marsh surface at the onset of marsh flooding during the same period, provide evidence that fish migrated into the impoundment and directly onto the marsh surface.
The marsh was flooded for over six months (55% of the time during the study period), allowing resident fishes to occupy the marsh surface continuously, far longer than would be typical for tidally influenced regions. For comparison, salt marshes in
Georgia are flooded on average about 26% annually, and salt marshes in Louisiana are flooded on average about 35% annually (estimated from Fig. 1; Kneib 1997). Of the
111
resident fishes on the marsh surface, the great increases in population biomass of C.
variegatus (4.2 times greater biomass leaving than entering) and F. grandis (8.5 times greater biomass leaving than entering) may indicate that they are best able to exploit saltmarsh foods and avoid predation. In tidal marshes, growth rates of larval F. heteroclitus positively correlated with marsh flooding duration (Kneib 1993). Resident fishes of the seasonally flooded marshes of the northern Indian River Lagoon may benefit from increased growth rates and reproductive output where they have the opportunity to exploit saltmarsh resources continuously; a hypothesis yet to be tested.
Intertidal fishes often face trade-offs between predation refuge and resource availability. Halpin (2000) recently evaluated the processes affecting habitat use by F.
heteroclitus. Caging experiments were deployed to measure F. heteroclitus growth
among various marsh habitats (creeks, pond, channel, mudflat), and tethering experiments
were undertaken to measure predation potential among the marsh habitats. Growth and
predation data were compared to the abundance of F. heteroclitus from field collections.
If predation refugia were available, F. heteroclitus occupied these even at the expense of
growth. Whenever predation risk was high across all available habitats, however, F.
heteroclitus occupied the habitat where growth was maximized. In one case, both high
growth potential and refuge from predation were available at one location.
Whether food and cover, or food only, influences resident fishes to occupy the
marsh surface in the present study depends on the relative rates of bird predation on the
marsh surface versus fish predation in the ditches and creeks. If piscivorous fish find
prey more effectively in ditch and creek waters than birds find the same prey on the marsh
surface, than greater cover may be present on the marsh surface. If so, biomass may build
112
up more on the marsh surface before the same level of predation occurs. Bird
aggregations, like the one that occurred in August during the study, suggest evidence that
birds aggregate during periods when resident fish density on the marsh surface is high
(fish had recently migrated into the impoundment and onto the marsh surface in
abundance). These bird aggregations may be an important regulatory factor for
minimizing overcrowding by resident fishes on the marsh surface, thereby resulting in
less density dependent mortality and more overall resident fish production. Alternatively,
if piscivorous bird and fish predation were equal, resulting in an absence of refuge,
resident fishes may have occupied the marsh surface where the greatest food was
available to maximize growth and reproduction, despite predation by birds.
Juvenile Transient Fish Hypotheses
The hypothesis that juvenile transient fish enter the impoundment, grow, and eventually emigrate to the estuary in greater biomass (although fewer individuals) than when they entered (Juvenile Transient Hypothesis 1) was supported by the greater number of M. cephalus in the impoundment than along the estuary shoreline, and the movement of transient fish from the impoundment to the estuary. Other transient species expected to use the low salinity, quiescent waters associated with Banana Creek salt marshes, such as S. ocellatus, C. nebulosus, E. saurus, and L. xanthurus, were not abundant in the study marsh as young juveniles. The distribution of juveniles, however, is spotty at best, and may be more influenced by spawning locations and transport patterns than by habitat quality alone (e.g., Ross and Epperly 1985). Thus, the specific site where this study was conducted may not have been in the right location to receive young juveniles other than
M. cephalus. The low number of transients along the estuary shoreline rejects the
113 hypothesis that young transient fishes are abundant along the shoreline, but absent from the impoundment (Juvenile Transient Hypothesis 2).
Large Piscivorous Fish Hypotheses
The abundance of large piscivorous fish was influenced by temperature and salinity as evidenced by the correlations between piscivorous fish catch per unit effort and temperature, and the abundance of L. platyrhincus (the dominant piscivorous fish) during low salinty. The low piscivorous fish catch per unit effort during winter may result from reduced activity of large fishes during periods of low water temperatures, or avoidance of the study area during winter. The absence of piscivorous fishes during low winter water levels allows resident fishes to leave the impoundment with minimum predation by large fishes.
The lack of recaptured fin-clipped piscivorous fish within the impoundment, combined with high abundance each month, suggest that the exchange of large predators between the impoundment and estuary was high. Large fish entered the impoundment for short periods (at least less than a month). Capture of large fish moving through culverts also supports the hypothesis that the exchange rate of piscivorous fish was high.
Although 53% of gill-net captured fish had empty stomachs, piscivorous fish stomachs did contain resident saltmarsh fishes. Thus, the hypothesis that large piscivorous fishes enter the impoundment, prey on resident saltmarsh fishes, and then leave (Large
Predatory Transient Hypothesis 1) was supported by the results. The alternative hypotheses that predators are more abundant along the estuary shoreline than in the impoundment, or enter the impoundment but die (Large Piscivorous Fish Hypotheses 2 and 3) were rejected because predators were not more abundant along the shoreline, and
114 there was no evidence that predators were trapped within the impoundment, or killed as a result of suboptimal water conditions, aside from freeze-kills.
Other Piscivorous Animals
Average annual piscivorous bird abundance in the study marsh (0.51 birds·ha-1) was less than the average reported for Merritt Island impoundments (0.62 birds·ha-1;
Smith and Breininger 1995). The highest abundance of birds occurs in saltmarsh impoundments that are closed nearly year round (Eric Stolen, Dynamac Corporation, pers. comm.), presumably where standing stock of saltmarsh fishes is greater as a result of longer hydroperiod, lower predation by transient fishes, and absence of fish migrations to the estuary. In the open impoundment of the present study, piscivorous bird abundance was influenced by major fish migrations as evidenced by the August bird aggregation on the marsh surface following migration of fish into the marsh, the aggregation along ditches and creeks as fish moved to these areas as water levels receded, and the correlation of mean piscivorous bird abundance with mean water level and net fish ingress. Another potential piscivore in the impoundment was A. mississipiensis, which were found within culverts probably to feed upon large transient species such as M. cephalus as they traveled through the culverts.
Fish Use of Marsh Habitats
The estuary shoreline, although vegetated with marsh plants, is not equivalent to the marsh surface with respect to fish community composition and abundance (Klassen
1998; and the present study). For example, the dominant species along the shoreline during the present study was F.carpio, an incidental marsh species, and not the typical suite of resident marsh species found within the impoundment. Furthermore, resident
115 fish densities were consistently greater within the impoundment habitats than along the shoreline. Not surprisingly, piscivorous wading birds were more abundant within the impoundment where their prey reaches higher densities, consistent with a previous study
(Smith and Breininger 1995).
Culverts connecting the impoundment to the estuary offer feeding opportunities to a variety of fish and wildlife as evidenced by the occurrence of large alligators within culverts, observations of birds feeding at culvert entrances, and presence of large piscivorous fishes feeding at culvert outfall plumes. Culverts confine water flow between the impoundment and estuary to a small area, thereby concentrating potential food sources for predators. A previous study found that culverts located near creek entrances or within embayments received the greatest use by fishes (Weiher 1995), and subsequent reconnection of impoundments by culverts often occurs at these locations, as was the case in the study impoundment. The greater export of fish biomass through culverts located at either end of the study impoundment (culverts 1 and 4; Fig. 10) probably occurred because fishes moving towards the estuary from the interior of the impoundment encounter these culverts first.
The perimeter ditch, although artificial, can be an important habitat for large piscivorous fishes seeking prey (Gilmore et al. 1982, Gilmore 1987; Rey et al. 1990b, and the present study). Water conditions in the study impoundment ditch (low dissolved oxygen and redox potential) were not substantially different than in adjacent Banana
Creek, and large transient piscivores were present there year round. Compared to many other Indian River Lagoon impoundments, the study impoundment is well connected (8 culverts connecting it to Banana Creek). Many impoundments have only one culvert and
116 this may not be open or maintained. Water conditions in the perimeter ditches associated with these, and other less actively managed impoundments, may be an important concern.
The deep-water ditch may initially attract transient fishes, but sudden degradation of water conditions due to inadequate circulation could kill these fishes resulting in a net
“sink” for transient fishes (Poizat and Crivelli 1997).
Impounded shallow creeks are a conspicuous feature in the northern Indian River
Lagoon, often separating adjacent impoundments, but little attention has been given to their value and potential restoration. The seasonal difference in resident fish use between the impoundment creek and the ditch may be related to changes in water level. The impoundment creek is much shallower than the perimeter ditch, which may explain its preference by resident fishes when water levels are low and the marsh surface is not available. The greater surface area of the creek may provide more food (e.g., microalgae), and cover (too shallow for piscivorous fishes), allowing resident fishes to maximize growth and minimize predation in the absence of marsh surface access. Thus, shallow creeks may provide an alternative habitat to the marsh surface for resident fishes during spring through summer. These creeks also appear to be important feeding areas for piscivorous fishes given high gill-net catch rates there.
Conclusions
Mugil cephalus may use the saltmarsh impoundment as nursery, but other expected nursery species (i.e., S. ocellatus, C. nebulosus, L. xanthurus) were not abundant as young juveniles within the impoundment or along the estuary shoreline. Resident marsh fishes are important forage for piscivorous fishes, and these predators regularly entered the marsh to prey upon marsh fishes in the study impoundment where eight
117 culverts connect it to the estuary. Also, piscivorous birds congregate within impoundments to feed upon resident fishes. Despite predation by fishes and birds within the impoundment, resident fishes leave the impoundment in far greater biomass than when they entered, substantially contributing to the estuary prey base. Although the movement of marsh production across the landscape by trophic relay occurred as large transients ate small residents and then left, the resident fishes themselves emigrated from the impoundment in substantial biomass, perhaps a unique occurrence of seasonally flooded salt marshes.
CHAPTER 5 BIOMASS BUDGET DERIVATION
Production Estimate from Ricker Equations
Numerous studies have estimated fish production from equations based on Ricker
(1946) as modified by Allen (1950) (a list of such studies is given in Day et al. 1989 and
Chapman 1978). The only data needed for these equations are changes (usually monthly) in fish standing stock (number and biomass). The basic equations are:
P = G·B, where:
G = (lnw2 - lnw1) / ∆t is the instantaneous coefficient of growth;
G-Z B = B1(e - 1) / (G - Z) is the average biomass;
Z = - (lnN1 - lnN2) / ∆t is the instantaneous coefficient of population change
attributable to mortality and migration; and w1 and w2 are the mean weights of
individuals at time t1 and t2, respectively, and N1 and N2 are the number of fish
present at time t1 and t2, respectively.
The model assumes that correction for immigration and emigration of fishes is not needed provided that fish density and size-class specific growth are estimated often enough to assess abundance and growth of fishes actually in the sampling area during each sampling period (Chapman 1978). In the present study, monthly estimated fish densities (from cast nets) were used to estimate fish production using these equations so that comparisons could be made with other estuarine fish production studies that used this method.
118 119
Production Estimate from Biomass Budget
The fish production estimate derived from Ricker’s equations lumps population changes due to migration and mortality into one variable (Z). The unique research opportunities provided by impoundments (dikes confine fishes into a known area and exchange of fishes are restricted to culverts), however, have made it possible to estimate rates of immigration, emigration, and potential consumption by piscivorous birds and fishes. These estimates, together with a production estimate, allow the relative yield to fishes, birds, and migration to be quantified.
The biomass budget for fishes within the impoundment (Fig. 2) did not fully reflect the sampling design. For example, deep habitats within the marsh (ditch and
Drainout Creek) were the areas where fish density was estimated (migrations to and from the marsh surface were not measured), fish migration was expressed as net ingress
(negative indicating net egress), and predation was estimated for both piscivorous fish and birds. A biomass budget of monthly fish production that incorporates these distinctions in the study design is shown in Fig. 45. The basic assumptions of the biomass budget are: 1) estimated densities of fish and rates of migration and predation resulting from monthly sampling were representative of the entire month, and 2) other disappearance (O) includes mortality aside from predation by fish and birds. Note that data are available only for production as P - O, an underestimate of total production (P) because the amount other disappearance (O) is unknown.
Estimates of Biomass Budget Parameters
Monthly fish population biomass was estimated from cast net sampling (Table
22). Population biomass for the ditch and creek was estimated by multiplying fish
120 densities within respective habitats by the area of each habitat. The area of the creek was determined from aerial photography by dividing the creek into small grids of known areas and counting the number of grids within the creek (area = 26,195 m2). The area of the perimeter ditch was determined by multiplying the length of the ditch as by its average width (area = 3,633 m length·10 m width = 36,330 m2).
Estimated population biomass was multiplied by 1.7 (100/60) to correct for cast net efficiency. Cast net efficiency was assumed to be similar to throw trap efficiency, which was estimated to be about 60% (Jordan et al. 1997). The removal efficiency of cast nets (likelihood that fish caught by the gear can be removed without escaping) would probably be lower than for throw traps because the trap-clearing procedure for throw traps is usually very thorough (e.g., traps are cleared with a bar seine until more than three empty bar seine passes occur), whereas the clearing procedure for cast nets is dependent on the net closing effectively upon retrieval. Catch efficiency (inverse of gear avoidance), however, would probably be greater for monofilament cast nets, which deploy more quickly and are less visible. Thus, the overall efficiency should be similar to throw traps.
Monthly estimates for net fish ingress were calculated by multiplying hourly culvert averages by hours in the month, and by the number of open culverts (Table 23).
Because fished and unfished culverts did not significantly differ in catch (Table 9), average catch in the four fished culverts was assumed to represent the remaining unfished culverts. The estimate of net fish ingress was corrected for culvert trap efficiency. A trap avoidance estimate of 40% was used with the rationale that certainly not all, but probably more than half, of fish biomass attempting to move through culverts enter the traps. The
121 inverse of estimated trap avoidance (catch efficiency; 60%) was multiplied by the retention efficiency determined in this study (25%) to give the overall estimated efficiency of the culvert traps (equal to 15%). Net fish ingress values were multiplied by
6.7 (100/15) to account for culvert-trap catch efficiency.
To determine the daily consumption of marsh fishes by piscivorous fish, an estimate of impoundment fish abundance was needed (Table 24). Good water clarity during April 2001 allowed for a count of L. platyrhincus, which remains close to the surface and conspicuous. Counts of L. platyrhincus in a given area were extrapolated to the entire impoundment (Table 25). Using a conversion factor from this method, however, assumes that all other piscivorous fish species are caught similarly to L. platyrhincus in the gill nets.
Daily prey consumption by piscivorous fishes was based upon published values for estuarine fishes (Table 26). Hunt (1960) and McGoogan and Gatlin (1998) estimated prey consumption from feeding experiments. Buckel et al. (1999) estimated prey consumption from diet analyses, and Hartman and Brandt (1995) and Hartman (2000) estimated prey consumption from both diet and observed growth rates. An estimate of
0.04 g wet prey·d-1 per g predator body weight (intermediate among literature estimates) was used in the biomass budget. For each month, the estimated population biomass of piscivorous fishes (g piscivorous fish·marsh-1) was multiplied by estimated consumption by piscivorous fishes and extrapolated to the entire month (Table 27).
Bird consumption estimates used in the biomass budget were taken from published values (Table 28). Junor (1972) hand-reared piscivorous birds (darters, cormorants, and herons) and estimated daily prey consumption (g wet weight) by birds to
122
be 16% of the bird’s wet body weight. Kushlan (1978) summarized the relationship
between bird size and prey consumption for wading birds, Walsberg (1983) summarized
daily energy expenditure of free-living birds, and Birt-Friesen et al. (1989) estimated field
metabolism of free-living seabirds using doubly labeled water and activity budgets.
Average bird consumption·d-1 was generated for each piscivorous species by substituting the weight of a typical adult bird into each of four equations (Table 28). These average bird consumption estimates were multiplied by average monthly bird abundance within the impoundment and extrapolated to the entire month (Table 29).
Sensitivity Analysis of Biomass Budget
An analysis was performed on all biomass-budget parameter estimates to
determine the sensitivity of these parameters to the overall fish production estimate (total
g fish· impoundment-1·yr-1). Each parameter estimate was individually increased by
30% and also decreased by 30%, and the production calculation was recomputed. The
changed budget parameters included: creek fish density, ditch fish density, creek area,
ditch area, cast net gear efficiency, net fish ingress catch per unit effort, culvert trap gear
efficiency, sum gill net catch per unit effort, conversion from gill net catch per unit effort
to population estimate, daily consumption by piscivorous fish, bird abundance, and daily
consumption by birds.
Table 22. Estimates of monthly fish standing stock (∆X) within Impoundment C20C (from cast net sampling).
Fish Density Habitat Area Population Biomass Standing Stock ∆ Standing Stock
Creek Ditch Creek Ditch Creek Ditch (g fish·impound-1·mo-1) (g fish·impound-1·mo-1)
-2 -2 -2 a (g fish·m )(·26,195 m ) (·36,330 m ) (·Gear Efficiency (1.7)) (month2-month1)
Jul 0.6 2.2 15,637 81,001 26,583 137,702 164,284 199,520 Aug 3.4 3.5 88,609 125,394 150,635 213,170 363,805 -353,564 Sep 0.0 0.2 0 6,024 0 10,241 10,241 181,479 Oct 0.5 2.7 14,167 98,610 24,083 167,637 191,720 -75,705 Nov 0.1 1.8 2,072 66,173 3,522 112,493 116,015 1,175,798
Dec 5.6 16.9 147,470 612,420 250,699 1,041,114 1,291,813 1,601,777 123 Jan 11.6 38.5 302,763 1,399,349 514,697 2,378,893 2,893,590 -1,181,370 Feb 16.0 16.2 419,013 588,175 712,322 999,898 1,712,220 -1,225,555 Mar 2.0 6.5 51,588 234,685 87,700 398,965 486,665 331,841 Apr 9.2 6.6 241,719 239,755 410,922 407,583 818,506 232,533 May 20.0 2.6 522,614 95,644 888,443 162,595 1,051,038 -87,329 Jun 8.4 9.6 218,815 348,073 371,986 591,724 963,710 909,167 July 32.8 6.7 859,353 242,339 1,460,900 411,976 1,872,876
aAssumed to be similar to throw trap efficiency (throw trap efficiency ~ 60% (Jordan et al. 1997))
Table 23. Estimates of monthly net fish ingress (Med) into Impoundment C20C (from culvert trap sampling). Negative values indicate net egress.
Month Net Fish Ingress Gear Efficiencya Net Fish Ingress (g fish·culvert-1·hr-1) (·24 hr) (·no. d·mo-1) (·8 culverts) (·6.7) = (g fish·impound-1)
Jul 15.6 374 92,850 2,995 622,092 Aug -3.1 -75 -18,531 -598 -124,160 Sep 0.3 8 1,994 66 13,362 Oct -8.1 -195 -48,456 -1,563 -324,654 Nov 0.0 1 125 4 835 Dec -6.0 -144 -35,803 -1,155 -239,882 Jan -25.3 -607 -150,533 -4,856 -1,008,572
Feb -11.5 -275 -61,704 -2,204 -413,418 124 Mar -6.3 -150 -37,217 -1,201 -249,355 Apr -3.2 -77 -18,511 -617 -124,027 May -0.8 -20 -4,877 -157 -32,673 Jun -13.2 -316 -75,853 -2,528 -508,217
aAssuming 60% trap catch efficiency and 25% retention efficiency (determined by adding fin-clipped fish to culvert trap and counting percent that are recaptured), the overall trap efficiency was 15% (0.60 times 0.25).
125
Table 24. Estimate of Florida gar abundance within the impoundment.
No. of gar observed between Area between Gar Area Area of Impoundment culverts 1 and 2 culverts 1 and 2 density of ditch Drainout Creek gar population (no.) (m2) (fish·m-2) (m2) (m2) (no. fish)
28 4,150 0.006747 36,330 13,000 332
Table 25. Conversion from catch per unit effort (no. gar· 10 m net-1·hr-1) to impoundment gar population.
No. of gar caught Number of 10 m Hrs Gill net net lengths fished catch per unit effort deployed
612.32.6 11 3 2 1.8 612.52.4 7123.5
Total gill net catch per unit effort 10.3
Total gill net catch per unit effort (10.3) / impoundment gar population (332) = 0.03
Thus, gill net catch per unit effort represents 3% of impoundment gar population
Multiply catch per unit effort by ~30 to convert to impoundment gar population
Table 26. Daily prey consumption per predator body weight for selected estuarine fishes. An estimate of 0.04 g prey consumed·d-1 per g body weight predator was used in the model.
Age g wet prey consumed· Reference Species Class predator wet body weight-1·d-1
Hunt (1960) Lepisosteus platyrhincus Juvenile 0.0281 Hartman and Brandt (1995)a Cynoscion regalis 1 0.051 Cynoscion regalis 2 0.036 Pomatomus saltatrix 0 0.048 Pomatomus saltatrix 1 0.043 Pomatomus saltatrix 2 0.037 McGoogan and Gatlin (1998)b Sciaenops ocellatus Juvenile 0.014 - 0.023
Buckel et al. (1999) Pomatomus saltatrix 0 0.04 - 0.12 126 Hartman (2000) Morone saxatilis 0 0.0326 - 0.0559
Average 0.037 - 0.049
aAfter accounting for estuarine residency of each species and maximum weight of each size class. bConversions: assimilation efficiency = 0.80 (for kJ digestable energy to kJ prey intake), 1 kJ = 0.23892 kcal, 1 kcal = 0.833 g wet biomass.
Table 27. Estimates of monthly fish consumption by piscivorous fishes (Yf) within Impoundment C20C.
sum g fish Conversion from sum CPUE sum g fish consumed g fish consumed· CPUE-1 to Populationa impound-1·d-1 = impound-1·mo-1 (·30 CPUE impound-1) (·0.04) (·no. d·month-1)
Jul 1,173 35,205 1,408 31 43,654 Aug 1,204 36,131 1,445 31 44,803 Sep 9,552 286,546 11,462 30 343,855 Oct 2,121 63,629 2,545 31 78,901 Nov 1,278 38,333 1,533 30 45,999 Dec 3,166 94,981 3,799 31 117,776 Jan 2,262 67,856 2,714 31 84,141
Feb 736 22,094 884 28 24,745 127 Mar 1,367 41,025 1,641 31 50,871 Apr 6,962 208,856 8,354 30 250,628 May 635 19,046 762 31 23,617 Jun 14,225 426,745 17,070 30 512,095
aConversion from gill net catch per unit effort to fish population (Table 26).
Table 28. Daily fish consumption (wet g fish·d-1) by piscivorous birds. The average consumption values for each species were used in the model estimate of prey consumption by piscivorous birds.
Consumption (g fish·d-1)
Species Common Name Weighta Junorb Kushlanc Walsbergd Birt-Friesen et al.e Average (g) (1972) (1978) (1983) (1989)
Pelecanus occidentalis* brown pelican 3,723 596 614 385 632 557 Mycteria americana* wood stork 2,724 436 455 318 504 428 Ardea herodias* great blue heron 2,588 414 433 309 485 410 Phalacrocorax auritus* dbl.-crested cormorant 1,816 291 308 249 375 306 Anhinga anhinga* American anhinga 1,226 196 211 196 282 221 Casmerodius albus* great egret 908 145 158 163 227 173
Nycticorax nycticorax* blk.-crown. night heron 863 138 151 158 218 166 128 Dichromanassa rufescens* reddish egret 454 73 81 107 137 99 Hydranassa tricolor* Louisiana heron 409 65 74 100 127 92 Egretta thula* snowy egret 363 58 66 93 116 83 Florida caerulea* little blue heron 363 58 66 93 116 83 Butorides striatus* green heron 227 36 42 70 83 58 Megaceryle alcyon* belted kingfisher 136 22 26 51 57 39 aWet weight of adult birds (Terres 1980) by = 16% weight of bird·d-1, y = g wet weight prey·d-1 clog y = 0.96 log x - 0.64, y = g wet weight prey·d-1, x = weight of bird (g) dln y = ln 12.84 + 0.61 ln (M), y = kJ prey·d-1, M = weight of bird (g) elog y = 2.99 + 0.727 log x, y = kJ energy expenditure·d-1, x = weight of bird (kg)
Conversions: assimilatoin efficiency = 0.80 (for kJ energy expenditure to kJ prey intake), 1 kJ = 0.23892 kcal, 1 kcal = 0.833 g wet biomass
Table 29. Estimates of monthly fish consumption by birds (Yb) within Impoundment C20C.
Average Consumptiona Monthly Consumption g fish·d-1·impound-1 (*no. d·month-1) (g fish·mo-1·impound-1)
Jul 3,257 31 100,957 Aug 14,719 31 456,292 Sep 1,314 30 39,410 Oct 5,660 31 175,447 Nov 1,917 30 57,515 Dec 1,008 31 31,236 Jan 3,848 31 119,273 Feb 1,516 28 42,454
Mar 388 31 12,036 129 Apr 275 30 8,258 May 421 31 13,058 Jun 868 30 26,046 a Average monthly abundance for each species was multiplied by their respective daily consumption rate (Table 30), and the results were summed to yeild g fish consumed·impoundment-1·month-1.
130
Variables: Subscripts:
P = production e = estuary (A = assimilation, R = respiration) d = ditch and creek habitat X = impoundment fishes b = birds (resident, incidental, and transient fishes) f = fish (piscivorous fish only) I = ingress s = marsh surface E = egress Y = yield to predators O = other disappearance
Pd (=Ad - Rd) Ps (=As - Rs)
E Ied ds
Xd Xs Isd Ede
Ydb Y df Od Ysb Ysf Os
∆X = change in accumulation x in a finite amount of time (∆t)
∆Xd = ∆Xd/∆t = Ied + Pd + Isd – Ede – Ydb – Ydf – Eds – Od
∆Xs = ∆Xs/∆t = Eds + Ps – Isd – Ysb – Ysf – Os
Net ingress from marsh surface = Msd = Isd – Eds
Net ingress through culverts = Med = Ied – Ede Migrations to and from the marsh surface cancel Pd = ∆Xd + Ydb + Ydf + Od - Med - Msd
Ps = ∆Xs + Ysb + Ysf + Os + Msd
Let P = Pd + Ps = (∆Xd + ∆Xs)+ (Ydb+Ysb) + (Ydf + Ysf) + (Od + Os) - Med
Let ∆X = ∆Xd + ∆Xs Yb = Ydb + Ysb
Yf = Ydf + Ysf O = Od + Os
Thus, P = ∆X + Yb + Yf + O - Med
Fig. 45. Derivation of fish production equation for biomass budget.
CHAPTER 6 BIOMASS BUDGET RESULTS
Fish production calculated using Ricker’s equations was 22.6 g fish·m-2·yr-1
(Table 30). The results of the production calculation using the biomass budget are given
in Table 31, which includes monthly estimates for standing stock, consumption by
piscivorous fishes and birds, and net fish ingress. Over the study period, 1.6 metric tons
of saltmarsh fishes were consumed by piscivorous fishes, 1.1 metric tons were consumed
by birds, and 2.4 metric tons were exported directly from the salt marsh to the estuary.
On the basis of saltmarsh area, direct export was about 5.6 g fish export·m-2 marsh·yr-1
(2,388,668 g fish export·yr-1 / 427,000 m-2 marsh)
Biomass budget output (production estimate P - O) did not change by more than
12% when changes to input parameters were varied by 30% (Table 32). Changes to creek fish density or creek area had a greater effect upon fish production estimates than did ditch fish density or ditch area. Manipulation of cast-net gear efficiency resulted in output changes of 7 to 8%. For example, if cast-net gear efficiency were 45% instead of the estimated 60%, then estimated fish production would increase from 6.800 x 106 to
7.313 x 106 g fish·impoundment-1·yr-1 (up 7%). Manipulation of consumption parameters also resulted in changes to output of 7 to 8%. If the conversion from gill-net catch per unit effort to impoundment piscivore population were 21 rather than the estimated 30 (gill net catch per unit effort represents 4.8% of the impoundment piscivore
131 132 population rather than 3%), then estimated fish production would decrease from 6.800 x
106 to 6.314 x 106 g fish·impoundment-1·yr-1 (down 8%).
The most influential parameters were those associated with net fish ingress estimates. Manipulation of culvert trap catch per unit effort or efficiency parameters resulted in changes to output up to 12%. For example, if culvert trap efficiency were 20% instead of the estimated 15%, then estimated fish production (P - O) from the biomass budget would decrease from 6.800 x 106 to 6.084 x 106 g fish· impoundment-1·yr-1 (down 12%).
Table 30. Fish production within Impoundment C20C estimated from Ricker's equations.
Month Fish density Ln (fish density) Z Fish density Ln (fish density) G B avg P = GB (no.fish·m-2)(no.fish·m-2)(no.fish·m-2)(g·m-2)(g fish·m-2)(g fish·m-2)(g fish·m-2)(g fish·m-2)
Jul 0.1 -2.0 2.0 1.4 0.3 0.9 0.9 0.8 Aug 1.0 0.0 -2.4 3.4 1.2 -3.7 1.9 -7.1 Sep 0.1 -2.4 0.5 0.1 -2.5 3.0 0.4 1.1 Oct 0.2 -1.9 0.9 1.6 0.5 -0.5 0.9 -0.5 Nov 0.4 -1.0 3.6 1.0 -0.1 2.5 0.6 1.4 Dec 13.4 2.6 1.0 11.2 2.4 0.8 10.4 8.3 Jan 35.2 3.6 -1.2 25.0 3.2 -0.4 38.1 -16.9 Feb 10.3 2.3 -1.0 16.1 2.8 -1.3 13.6 -18.3 Mar 3.8 1.3 0.2 4.2 1.4 0.6 5.3 3.4
Apr 4.5 1.5 0.8 7.9 2.1 0.4 6.5 2.3 133 May 9.7 2.3 -1.2 11.3 2.4 -0.2 19.3 -4.5 Jun 2.9 1.1 1.3 9.0 2.2 0.8 6.9 5.4 July 10.9 2.4 19.7 3.0
Total Production = 22.6
P = GB, where:
G = (lnw2 – lnw1) / ∆t is the instantaneous coefficient of growth; G-Z B = B1(e -1) / (G-Z) is the average biomass;
Z = - (lnN1 – lnN2) / ∆t is the instantaneous coefficient of population change attributable to mortality and migration;
and w1 and w2 are the mean weights of individuals at time t1 and t2, respectively,
and N1 and N2 are the number of fish present at time t1 and t2, respectively.
Table 31. Fish production within Impoundment C20C estimated from biomass budget: P - O = ∆X + Yf + Yb - Med
g fish·impound-1·mo-1
Month ∆X Yf Yb Med P-O
Jul 199,520 43,654 100,957 622,092 -277,961 Aug -353,564 44,803 456,292 -124,160 271,691 Sep 181,479 343,855 39,410 13,362 551,382 Oct -75,705 78,901 175,447 -324,654 503,296 Nov 1,175,798 45,999 57,515 835 1,278,477 Dec 1,601,777 117,776 31,236 -239,882 1,990,671 Jan -1,181,370 84,141 119,273 -1,008,572 30,616 Feb -1,225,555 24,745 42,454 -413,418 -744,939
Mar 331,841 50,871 12,036 -249,355 644,103 134 Apr 232,533 250,628 8,258 -124,027 615,445 May -87,329 23,617 13,058 -32,673 -17,981 Jun 909,167 512,095 26,046 -508,217 1,955,524
Total 1,708,592 1,621,084 1,081,981 -2,388,668 6,800,326a
X = Standing Stock Med = Net Migration from impoundment
Yf = Consumption by piscivorous fish O = Other disappearance
Yb = Consumption by piscivorous birds
Table 32. Sensitivity analysis of impoundment fish biomass budget.
Input Parameters Output Characteristics (g marsh-1 mo-1)
Changed increase/ Std. ∆X Yf Yb Med P-O % Change in Parameter* decrease Value (1,708,592) (1,621,084) (1,081,981) -(2,388,668) (6,800,326) P-O
Creek density incr. 26,195 m-2 2,138,887 7,230,621 6 decr. 1,278,297 6,370,030 -7
Ditch density incr. 36,330 m-2 1,790,874 6,882,608 1 decr. 1,626,310 6,718,043 -1 135
Creek area incr. ** 2,138,860 7,230,593 6 decr. 1,278,269 6,370,003 -7
Ditch area incr. ** 1,790,874 6,882,608 1 decr. 1,626,310 6,718,043 -1
Cast net gear efficiency incr. 1.7 2,221,170 7,312,903 7 decr. 1,196,014 6,287,748 -8
Net migration CPUE incr. ** -3,105,269 7,516,926 10 decr. -1,672,068 6,083,725 -12
Culvert trap gear efficiency incr. 6.7 -3,105,269 7,516,926 10 decr. -1,672,068 6,083,725 -12
Table 32. Continued
Sum gill net CPUE incr. ** 2,107,409 7,286,651 7 decr. 1,134,759 6,314,000 -8
Conversion CPUE to Pop. incr. 30 2,107,409 7,286,651 7 decr. 1,134,759 6,314,000 -8
Daily consump. by fish incr. 0.04 2,107,409 7,286,651 7 decr. 1,134,759 6,314,000 -8
Bird abundance incr. ** 1,406,576 7,124,920 -5 decr. 757,387 6,475,731 5
Daily consump. by birds incr. ** 1,406,576 7,124,920 -5 136 decr. 757,387 6,475,731 5
* Parameters were increased and decreased by 30% ** Each month was increased and decreased by 30% to make the adjustment
CHAPTER 7 BIOMASS BUDGET DISCUSSION
Assuming that standing stock, consumption, and migration estimates (based on direct sampling) used in the fish biomass budget were accurate, then negative values resulting from the biomass budget were attributable to mortality (other than predation) and marsh surface migrations. Negative production (P - O) values in July and May were probably the result of fish migrating from the ditch and creek (where standing stock is measured) to the marsh surface, because water levels exceeded the threshold of marsh flooding allowing fish to move onto the marsh surface (Fig. 46). High production (P - O) values in December and June probably resulted from fish migrating from the marsh surface back to the ditch and creek as water drained the marsh (Fig. 46). Over the long run, marsh surface migrations should cancel (Fig. 43). For example, fish leaving the ditch and creek to the marsh surface in July may result in negative production values, but when the fish return to the ditch and creek in December, this production is added back in addition to fish production that occurred on the marsh surface. Thus, correcting for marsh surface migrations is not necessary to estimate total production during the study.
Negative production also occurs in February, which cannot be explained by marsh surface migrations because water levels remained low through the following month. This negative production occurred following a month where fish densities were the highest
(~35 fish·m-2) and freezes occurred. If the negative fish production is attributable to
mortality caused by freezes or density-dependent effects, then this other disappearance
137 138
(O) should be added to production. Assuming O is negligible aside from the February
mortality, total fish production in the study impoundment was estimated at 7.545 x 106 g
fish·impoundment-1·yr-1 (Table 33). On an aerial basis (combining impoundment fish
habitats: ditches, creeks, and marsh surface), production for the study impoundment was
17.7 g fish·m-2·yr-1 (7.545 x 106 g fish·impoundment-1·yr-1 / 4.27 x 105 m2·
impoundment-1).
The model based upon Ricker’s equations exceeded fish production derived from
the biomass budget by 4.9 g fish·m-2·yr-1. Nevertheless, fish production estimates for the study impoundment are within the range of published estimates of estuarine fish communities (Table 34). Fish production estimates range from 2.6 g fish·m-2·yr-1 for seagrass fish communities in Mosquito Lagoon, Florida, to well over 30 g fish·m-2·yr-1
for coastal and estuarine fish communities in Mexico, Louisiana, and California.
Closed saltmarsh impoundments, located only 8 and 28 km to the north of the
study impoundment, were at least 13.8 g fish·m-2·yr-1 more productive than the study impoundment (Schooley 1980, Table 34). The closed impoundments studied by
Schooley (1980) also had higher average numerical fish density (16 – 27 fish·m-2
compared to 7 fish·m-2) and turnover (3.0 – 3.7 compared to 2.3 - 2.6). Studies
comparing open and closed impoundments in the Indian River Lagoon, Florida, have
shown that resident fish densities are much higher in closed impoundments (Rey et al.
1990a; Taylor et al. 1998). Greater standing stock of resident fishes in closed systems
may result from prevention of resident fish migration to the estuary and reduction in
transient estuarine predators. Another explanation for greater standing stock of resident
fishes is higher fish production rates due to greater food resources (e.g., microalgae or
139
mosquito larvae), greater food quality, and/or greater access to food as a result of longer
flooding. Although fish production may be higher in closed impoundments, the biomass
is trapped within the closed system, except for transfer by bird predation.
The proportion of consumption and migration of saltmarsh fish biomass relative
to total fish production is shown in Fig. 47 (results derived from Table 33). Overall
mortality by biomass (combining other disappearance and consumption by fishes and
birds) was 45% per year. Mortality rates were estimated at 0.023 – 0.041% d-1 (~ 8.4 -
15.0% yr-1) for L. xanthurus (e.g., Currin et al. 1984), 23% - 61% (two-week mortality)
for Penaeus aztecus, (Minello et al. 1989), and as high as 50% per year for mummichog
F. heteroclitus (Meredith and Lotrich 1979). Note that 23% of fish production was attributable to changes in standing stock (Fig. 47). This means that fish standing stock accumulated during the study period. This fish production may enter one of the pathways shown in Fig. 47 (emigration, consumption, or other disappearance) sometime in the future. If the fish production accumulated as standing stock is prorated among the pathways, then an additional 5% of fish production will be consumed by piscivorous fish, another 4% will be consumed by piscivorous birds, an additional 2% will be lost to other disappearance, and another 7% will emigrate to the estuary.
Direct export of fish biomass was estimated to be at least 32% (Fig. 47).
Assuming a 10% energy transfer for each increase in trophic level, piscivorous fishes potentially move an additional 2.1% to the adjacent estuary after consuming 21% of saltmarsh fish production. Thus, about 34% of fish production was exported from the salt marsh to the adjacent estuary. In closed impoundments in Mosquito Lagoon, Florida, the transfer of net primary marsh production to fish production (fish production / net marsh
140 production) was estimated at 6.5% (Schooley 1980). Multiplying this transfer ratio
(6.5%) by exported fish production (34%), the saltmarsh primary production that moved to the estuary in the tissues of fish was about 2%.
Of greater importance in evaluating the significance of saltmarsh production and export to the estuary is not the quantity of exported production, but the quality.
Qualitative factors include energetic content, protein content, and nutrient content of food sources. Small juvenile transient fishes incorporate marsh foods into their tissues as they consume detritus and algae from saltmarsh creeks. Residents are able to cover the shallow marsh surface, thereby consuming marsh foods that would otherwise be difficult for transient fishes to access (Werme 1981). The quality of these marsh foods is concentrated as they are incorporated into the tissues of fish. For example, detritus contains about 1 – 2% nitrogen (Day et al. 1989; Deegan 1993), whereas fish tissue contains more than 17% nitrogen (Deegan 1993). Also, fish tissue has concentrated levels of protein and lipids relative to detritus (Deegan 1993). From the perspective of large estuarine fish, such as C. nebulosus and S. ocellatus, the quality of resident and small transient fish tissues is readily useable. Thus, marsh fishes not only move saltmarsh production to the estuary, but also convert low quality saltmarsh foods to higher quality vagile biomass, providing an efficient link between salt marshes and higher trophic carnivores in the adjacent estuary.
Table 33. Estimated fish production incorporating net fish ingress from marsh surface and other disappearance
(P = ∆X + Yf + Yb + O - Med).
g fish·impound-1·mo-1
∆X Yf Yb Med OP
Totals from Table 32 1,708,592 1,621,084 1,081,981 -2,388,668 744,939 7,545,265*
Percent of production 23% 21% 14% 32% 10%
X = Standing Stock Med = Net Migration from impoundment 141 Yf = Consumption by piscivorous fish O = Other disappearance
Yb = Consumption by piscivorous birds
* Over the course of the study, the effects of marsh surface migrations (Msd) cancel (see discussion). Assuming negative production during February (-744,939) is attributable to O, and O is negligible aside from February, impoundment fish production ~ 7,545,000 g·yr-1.
Table 34. Estimates of fish production among estuarine communities. References are from Table 10.3 in Day et al. (1989), except Schooley (1980), Adams (1976), and Allen (1982).
Reference Fish community Location Fish production (g m-2 yr-1)
Schooley (1980) Seagrass Mosquito Lagoon, Florida 2.6a Hellier (1962), Jones et al. (1963) Estuarine Laguna Madre, Texas 12.1 - 57.6a Adams (1976) Seagrass North Carolina 18.4a Present study Salt marsh Banana Creek, Florida 17.7b, 22.6c Yanez-Arancibia and Lara Dominguez (1983) Lagoon Terminos Lagoon, Mexico 20.0a Holcik (1970) Coastal lagoon Cuba 22.0 - 27.6a Yanez-Arancibia (1978) Coastal lagoon Mexico, Pacific coast 24.6 - 66.7a 142 Warburton (1979) Coastal Mexico, Pacific coast 34.5a Day et al. (1973), Wagner (1973) Estuarine Barataria Bay, Louisiana 35.0 - 72.8a Allen (1982) Littoral zone of tidal marsh California 37.4a Schooley (1980) Saltmarsh impoundments Mosquito Lagoon, Florida 38.8 - 59.2a 31.5 - 40.0c
a Based on summation of production estimates for component species b Based on fish biomass budget: annual fish production / area of salt marsh c Based on production equations in Ricker (1946) modified by Allen (1950) and Chapman (1978), but substituting monthly biomass of whole community rather than summation of species
2500000 Fish Production 0.8 Water Level Fish concentrate into ditch and creek from Marsh Elevation 0.7 2000000 flooded marsh surface )
-1 0.6 1500000
0.5 1000000
0.4
500000 0.3 143 0 0.2 W and Marsh ater Level Elevation (m) Impoundment Fish Production (g·yr
-500000 Fish leave ditch for Fish leave ditch for 0.1 flooded marsh surface flooded marsh surface
-1000000 Other disappearance 0 Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Month (2000 - 2001)
Fig. 46. Estimated fish production (g··yr-1), water level (m), and marsh elevation (m) in Impoundment C20C during study period.
144
Consumption and Migration of Impoundment Fish Production Avian wildlife
14% (18%)
32% (39%) Saltmarsh Fishes
10% (12%)
21% (26%)
Other Large Disappearance Piscivorous Fishes
Fig. 47. Consumption and migration of fish production from Impoundment C20C. The remaining 23% of fish production was attributable to changes in standing stock. This surplus standing stock may later enter one or several of the above pathways. Numbers in parentheses show percentage of production if this 23% increase in standing stock over the study period is prorated among the pathways.
CHAPTER 8 OVERALL DISCUSSION
Impoundment Management Strategies
Many of the saltmarsh impoundments within MINWR are presently managed for mosquito control, and/or wildlife. Note that both forms of management involve diking and passively controlling water levels with structures (Fig. 48). However, the desired water level and schedule of water exchange through the structures differ, with differing consequences for both key prey-base species and important resource species (i.e., federally listed endangered species, sport fishes, wading birds, waterfowl, raptors, and song birds).
In mosquito control management (specifically Rotational Impoundment
Management), high water level is maintained during summer (closing water control structures and possibly pumping lagoon water into the impoundment if needed) to discourage saltmarsh mosquito production. During the remainder of the year, culverts can be left open to encourage impoundment use by estuarine fishes (rotational impoundment refers to the summer closure, followed by opening in fall through spring)
(Brockmeyer et al. 1997).
The life cycle of saltmarsh mosquitos Aedes taeniorhynchus and A. sollicitans is as follows: mosquitos lay their eggs on moist soil, when the marsh is flooded, eggs hatch and adult mosquitos emerge from the water 7 to 15 days later (Provost 1977). Flooding the marsh during the saltmarsh mosquito-breeding season breaks the mosquito
145 146 reproductive cycle because they are not able to lay eggs directly on or in the water. Water level results from datasondes in the study marsh (Fig. 12) show why mosquito production is so prevalent in the northern Indian River Lagoon without mosquito control. During summer, the marsh is periodically flooded at one to two week intervals, which is ideal for the mosquito breeding cycle (Ritchie and Montague 1995). Mosquitos are able to lay eggs on moist soil, and then the marsh is flooded for more than one week allowing the larvae to develop as adults. Following the production of a mosquito brood, the marsh drains once again allowing the cycle to repeat immediately. Mosquito production can also occur in isolated potholes and depressions on the marsh surface, particularly at high marsh elevations, as rainfall periodically fills these areas (Harrington and Harrington
1961).
Wildlife Aquatic Management (WAM) is a brackish water management regime
(target salinities between 8 and 18 ‰) intended to provide seasonally fluctuating water depths to maintain native wetland plant and wildlife communities (MINWR
Comprehensive Management Plan). Maintaining productive populations of resident marsh fishes is particularly important to wading bird management (MINWR
Comprehensive Manangement Plan). Typically, high water level is maintained during fall and winter for migratory waterfowl use, and water levels are drawn down during
March and April to concentrate prey for nesting wading birds and expose mudflats for migratory shorebirds (MINWR Comprehensive Manangement Plan). Without management, water level would have receded by February, approximately two months short of the wading bird nesting season (Smith and Breininger 1995), a time when additional wading bird food resources are needed for reproduction. During summer, the
147
impoundment is allowed to be flooded (by rainfall or by pumping lagoon water into the
impoundment), providing mosquito control. Thus, impoundment water control structures
are in place, and water is impounded during the majority of the year.
Implications of Impoundment Management Strategies
Previous studies have addressed the effects of mosquito control management on
access by large transient fishes in this region (Gilmore et al. 1982; Gilmore 1987; Rey et
al. 1990a, 1990b). When water control structures were open in fall, coastal wetland
impoundments were used by P. cromis, E. saurus, C. undecimalis, and also transient
forage-base species such as striped mullet M. cephalus (e.g., Gilmore et al. 1982; Gilmore et al. 1987; Rey et al. 1990a, 1990b). The only transient fish thought to be potentially affected by RIM was larval M. atlanticus, because closing water control structures during the mosquito-breeding season eliminate saltmarsh nursery habitat for this summer recruit.
Most other transients in the Indian River Lagoon recruit to marshes sometime during fall through spring when water control structures are open under RIM (Gilmore et al. 1982).
Summer closure under RIM appears to be compatible with resident fish migrations found during the present study. When impoundments are opened during early fall (August or September), resident fishes may migrate into impoundments. As water level recedes in late winter/early spring, resident fishes may migrate from the marsh surface to the estuary before the summer closure. Thus, RIM may not substantially affect the net resident fish biomass export function of Indian River Lagoon saltmarsh impoundments.
Closing water control structures during the majority of year, which is the case under a combination of WAM and RIM, benefits both waterfowl and wading birds
148
(Provost 1967; Smith and Breininger 1995). Impounded marshes provide feeding and resting opportunities for several species of ducks refueling their energy supplies along the
Indian River Lagoon coastline as they migrate south during winter (Provost 1959, 1967).
Reduced salinities and extensive shallow open-water areas, a target of WAM, encourage growth of common waterfowl foods such as Ruppia maritima and Chara spp. Ensuring suitable feeding and resting habitat to migrating avian wildlife in light of increasing habitat degradation and fragmentation is an important objective for resource managers
(Provost 1967).
Results of the present study illustrate how closing impoundments and flooding marshes can be an effective management strategy for optimizing prey access to wading birds. High water level allows for production of resident fishes on the marsh surface, and closed water control structures may inhibit immigration of large aquatic predators into the impoundment. Standing stocks of resident marsh fishes may increase when impoundments are closed because predation by piscivorous fish and egress of resident fishes are reduced. The period of flooding on the marsh surface is extended, thereby extending access to food and cover for resident fishes. When water levels are manipulated to provide optimal foraging depths for wading birds, greater consumption of resident fishes by birds may occur. Thus, the biomass budget (Fig. 47) would differ for closed impoundments by allowing more bird consumption, less piscivorous fish predation, and less fish emigration. Also, closing water control structures may increase primary productivity by reducing nutrient export (Zedler et al. 1980). Reduced salinities, an objective of WAM, may also enhance marsh primary production. Compared to salt marshes, production may be greater in brackish and freshwater marshes, detritus may be
149 more nutritious, and decomposition rates may be faster leading to greater secondary production (Montague et al. 1987).
Conflicts between Bird and Fish Management
Closed impoundments appear to benefit piscivorous birds and waterfowl (Provost
1967; Smith and Breininger 1995), but are not compatible with estuarine fish use of impoundments (Brockmeyer et al. 1997). The number of species found in marshes is reduced dramatically following impoundment (Harrington and Harrington 1961; Gilmore et al. 1982; Gilmore 1987). The species affected are transients that enter the marshes as juveniles and must eventually leave to reproduce. Thus, marsh-estuary connectivity is important for transient fish use and overall biodiversity of aquatic marsh communities.
Connection of the salt marsh with the estuary is needed for export of resident marsh fishes that represent food for estuarine predators. During the 1970s, when almost all Indian River Lagoon salt marshes were impounded (with no connection), fish production was trapped behind a system of dikes, and was unavailable for consumption by estuarine predators. At over 16,200 ha of salt marshes impounded (Brockmeyer et al.
1997), lost fish biomass to the estuary may have totaled more than 840 metric tons, annually (if pre-impoundment salt marshes exported fish biomass at the magnitude of the study impoundment, 5.2 g fish·m-2 marsh). For perspective, this value exceeds average
1996 – 1999 landings of striped mullet (a common forage base species) along the Atlantic coast by more than 200 metric tons (Mahmoudi 2000).
Although most impoundments have since been reconnected to the estuary
(Brockmeyer et al. 1997), many are still managed for both mosquito control and wildlife, where water control structures remain in place during most of the year. Thus,
150 management objectives for birds, combined with mosquito control, are in direct conflict with both salt marsh use by estuarine predators, and export of fish biomass. The best management strategy for fishes is to restore and maintain the hydrologic connection between the impoundment and the estuary completely. MINWR resource managers have addressed this conflict by continuing to manage selected impoundments for wading birds and other avian wildlife where water levels can be most effectively controlled, and reconnect/restore other impoundments to increase estuarine fish use (MINWR
Comprehensive Management Plan).
Impoundment Restoration Strategies
Several impoundment restoration strategies exist, ranging from simply leaving water control structures open year round to removing dikes and perimeter ditches completely (Fig. 49). Removal of dikes is accomplished by scraping dike sediment back into the perimeter ditch (usually with a dragline). Removing the dike without filling the ditch would require the removal of tons of sediment, whereas scraping the dike back into the ditch with a dragline is logistically easier and less expensive. Also, leaving the ditch in place without the protection of the dike from storms and tide would probably result in infilling of the ditch, which commonly occurs in areas where ditches were created for mosquito control at the boundary between marshes and estuary (Marc Epstein, MINWR biologist, pers. comm.). The perimeter ditch can be left in place if impoundment water control structures are simply left open year round. Maintaining impoundment dikes, but opening the water control structures also provides flexibility in habitat and resource management options.
151
Where impoundments are restored, rotary ditches are being created to provide adequate mosquito control (Fig. 49). Rotary ditches are relatively shallow (< 0.5 m depth), and narrow (1 m wide) (Duhring 1989), and therefore differ from the deeper and wider perimeter ditches. The rotary ditches are sufficient, however, for providing a hydrologic connection between marsh mosquito breeding “hot-spots” and the estuary.
They provide mosquito control by assuring that no water stands at the surface for more than a few days while providing larvivorous fish access to remaining standing water
(Duhring 1989).
Implications of Impoundment Restoration Strategies
Perimeter ditches, culverts, marsh surface, and estuary shorelines are directly affected by restoration efforts. The perimeter ditches and culverts would be eliminated if impoundments were restored completely by scraping the dike back into the ditch.
Perimeter ditches represent hundreds of miles of deep-water marsh habitat for a variety of fish and wildlife. For example, ditches and associated culverts were used by both piscivorous fishes seeking prey within the marsh, and those ambushing exported forage fishes. They were also found to be sites often used by A. mississipiensis, and a variety of birds (e.g., Butorides striatus, Ardea herodias, Magaceryle alcyon, Anhinga anhinga, and
Phalacrocorax auritus). If impoundments have adequate connection to the estuary
(several culvert locations), then opening water control structures seems to be the best option for restoring the estuarine ecosystem function of the salt marshes. Increasing access to salt marshes by simply opening water control structures allows fish and wildlife to use the impoundment for feeding via the perimeter ditch, and also allows emigration of resident fishes when they reach high densities.
152
Where implementation of adequate connection between impoundments and the
estuary is not practical (only one or two culverts can be added) due to logistical
constraints or uncertainties regarding future funding for impoundment maintenance, then
complete removal of impoundment dikes may be the best restoration option. Resident
fishes may remain crowded (and more would die) for much longer duration than in the
study impoundment where installing and maintaining numerous culverts is not practical.
Removing impoundment dikes could increase the cross-sectional area that fishes can use
to emigrate to the estuary, probably resulting in greater export of resident fishes, but at the
expense of the deep-water fish habitat offered by the perimeter ditch. Regardless of
restoration strategy (opening of sufficient number of culverts or complete removal of
dikes), the resident-fish biomass-export function of the Indian River Lagoon salt marshes
would be restored. If resident fish export from other restored saltmarsh impoundments in
the vicinity is similar to that of the study impoundment (5.2 g fish·m-2 marsh), then
resource managers can expect an export of 5.2 metric tons of small forage fish annually
for every 100 ha of impounded marsh opened.
A driving motivation for restoration has been to provide greater marsh access to
young transient fishes seeking nursery habitat (Brockmeyer et al. 1991). The expected
nursery species, however, were not abundant in the study impoundment. Moreover, a
series of impounded and restored marshes and associated shorelines sampled by throw
trap and cast net did not reveal many nursery species using the marshes (Florida
Caribbean Science Center, USGS, unpubl. data). Although C. undecimalis, E. saurus,
and M. atlanticus were the primary juvenile species found within previously studied barrier island impoundments located near inlets (Gilmore et al. 1982; McLaughlin 1982;
153
Karlen 1991; Weiher 1995; Poulakis 1996; Lin and Beal 1995; Taylor et al. 1998; Faunce and Paperno 1999), the MINWR impoundments are much farther from the oceanic sources of the larvae. Young juvenile transients, however, should occur within the northern Indian River Lagoon because some adult transients (e.g., S. ocellatus and C. nebulosus) are known to spawn there (e.g., Johnson and Funicelli 1991; Johnson et al.
1999). If the decision to increase marsh access to transient species continues to drive restoration, then attention should be given to locating marshes with potential for receiving young fishes. Areas with high potential for receiving young of year transients might include marsh impoundments adjacent to adult transient spawning sites, and impoundments where young transients are abundant along the adjacent estuary shoreline.
Relatively shallow and narrow rotary ditches added for mosquito control during restoration are probably not functionally equivalent to either deeper perimeter ditches (~1 m deep) or broader natural creeks with respect to fish use. They are probably too shallow to provide passage by large piscivorous fishes, and too narrow to provide an alternative to the marsh surface during seasonally low water levels. A possible benefit of rotary ditches may be to facilitate ingress and egress of marsh residents to and from the marsh surface during flooding and draining events. This would further provide a mosquito control benefit as larvivorous fishes could quickly access mosquito-breeding sites, and would probably provide a conduit for resident fish biomass export during marsh draining events.
Whether the rotary ditches offer habitat to young transient fishes during seasonally high water levels remains to be tested.
A final consideration for impoundment restoration is the aesthetic value of various restoration strategies. Removal of impoundment dikes creates the appearance of a
154
“natural marsh setting”. Creation of rotary ditches, if designed with meandering curves, can further contribute to the aesthetic value of marshes by creating a dendritic creek system reminiscent of tidal marshes. These aesthetic values can greatly contribute to recreational use of nearshore estuarine habitats, regardless of function, and are difficult to gauge in terms of value when deciding among restoration strategies. Determining the appropriate management or restoration strategy for each impoundment ultimately depends on value judgments among mosquito control, marsh vegetation, fish use, bird use, and aesthetics.
Conclusions
-- Saltmarsh impoundments that remain closed permanently, or during most of the year, appear (conceptually) to benefit wading birds by increasing resident fish standing stock and/or increasing resident fish production. Greater fish standing stock may occur by reducing large piscivorous fish ingress into the impoundment and resident fish export to the estuary. Greater fish production may occur by increasing primary production (by reducing salinity and nutrient export) and/or increasing fish access to the marsh surface
(marsh is flooded longer).
-- Although closed impoundments may benefit wading birds by trapping fish production within impoundments, they are in direct conflict with sound management of estuarine fish resources. The comprehensive management plan for Merritt Island National Wildlife
Refuge seems to offer the most appropriate resolution to this inherent conflict: manage impoundments for wading birds and other avian wildlife where management goals can be best accomplished, and reconnect/restore other impoundments to increase estuarine fish use.
155
-- The saltmarsh impoundment reconnected to the Indian River Lagoon was a major fish
biomass producer. Thus, maintaining and/or expanding saltmarsh impoundments that
remain “open” to the estuary is ecologically sound, as prey base species are exported to
the adjacent estuary bringing incorporated saltmarsh production with them. The exported
prey are then accessible to important estuarine resource species (i.e., sport fish, raptors,
and marine mammals such as dolphins) and may enhance their production.
-- With respect to resident fish biomass export, restoration of impoundment-estuarine
connectivity can be accomplished by either simply leaving culverts open year round or
complete removal of dikes. If installing and maintaining numerous culverts is not
practical, then removal of dikes may be a better option because adequate exit points for
fish appears to be important during critical periods of high fish density, and probably
during suboptimal water conditions if they occur.
-- Although an artificial human creation, perimeter ditches represent a deep-water habitat
that allows aquatic predators to seek prey within the salt marsh. The ditches are a
conspicuous feature of the marsh landscape and represent hundreds of miles of habitat for
large piscivorous fishes. The dike-ditch-culvert system also provides habitat for wildlife
such as alligators and piscivorous birds. Elimination of the ditch would greatly reduce
access to marsh prey by high profile resource fish species of the Indian River Lagoon
system (i.e., S. ocellatus, C. nebulosus).
-- The creek was statistically similar to ditches with respect to fish density when months were pooled, but creeks and ditches appeared to differ seasonally. The creek may represent an alternative habitat to the marsh surface for resident fish during low water periods. Creeks were also used extensively by high profile resource fish species seeking
156 prey during seasonally high water levels. Creek-estuarine connectivity may increase production and export of resident marsh fishes during seasonal low water, and also provides predator access to marsh prey.
-- If impoundment dikes were eliminated by restoration actions (for aesthetic reasons), then more “natural” appearing creek habitat could be created by dendritic rotary ditching to simulate natural drainage via marsh creeks, and also provide mosquito control if impoundments are eliminated. The function of these rotary ditches with respect to fish use would probably differ from the deeper perimeter ditches. The small rotary ditches may facilitate resident fish export from the marshes, but they would be too shallow to allow piscivorous fish access within the marsh.
RIM (Rotational Impoundment Management) WAM (Wildlife Aquatic Management)
marsh marsh high marsh high marsh water-control water-control perimeter ditchstructure perimeter ditch structure culvert dikeculvert dike
lagoon lagoon closed: sum.
closed: sum. - spring 157 open: fall - spring open: spring - sum. Definition Definition
Culverts were installed to manage for mosquito control, Water levels are controlled throughout most of the while providing exchange of water and aquatic year to encourage wildlife use of saltmarsh by organisms to the estuary when possible. Culverts are promoting production of vegetation and controlling closed in the summer, and water is retained on the water levels suitable for a diversity of wildlife. In marsh for mosquito control. Culverts are open fall - some impoundments, culverts are opened in spring, spring. and water is allowed to draw down to encourage germination of seed banks.
Fig. 48. Management strategies of coastal wetland impoundments in the Indian River Lagoon, Florida.
Open Culvert Breached
marsh marsh high marsh high marsh
perimeter ditch perimeter ditch culvert dike dike
lagoon lagoon 158
Definition Definition
One restoration strategy is to simply leave the culverts Culverts are removed and the dike is breached open year round to allow water level to fluctuate restoring connection between the perimeter ditch and naturally with the estuary. the estuary. However, the breach often fills with sediment, and water circulation becomes restricted
Fig. 49. Restoration strategies of coastal wetland impoundments in the Indian River Lagoon, Florida.
Restored (removal of dikes and ditches) Restored Open Water Management (OWM)
high marsh marsh high marsh marsh
lagoon lagoon 159
Definition Definition
The dike is pushed back into the perimeter ditch Rotary ditches connect mosquito "hot spots" to the restoring the original elevation of the marsh. estuary, improving the drainage of ponded water that allow mosquito larvae to develop. Some ponds may be deepened to reduce mosquito production and stabilize fish populations that feed on mosquito larvae.
OWM may be implimented in restored, open, and breached impoundments.
Fig. 49. Continued
APPENDIX A LENGTH-WEIGHT RELATIONSHIPS FOR FISHES
Table 35. Length-weight relationships for fishes collected within Merritt Island National Wildlife Refuge, Florida.
Loge(Wt) = Loge(TL)* a + b No. r Range (mm TL) Reference
Alpheus heterochaelis 3.062 -10.825 18 0.967 25-55 USGS Anchoa mitchilli 2.919 -11.256 39 0.950 17-66 USGS Cynoscion nebulosus 2.885 -10.970 21 0.994 29-422 USGS Cyprinodon variegatus 3.610 -12.855 349 0.991 17-52 USGS Elops saurus 2.964 -11.973 42 0.984 159-462 USGS Floridichthys carpio 3.385 -12.353 29 0.9939 47-69 USGS Fundulus confluentus 3.477 -13.063 28 0.996 30-71 USGS Fundulus grandis 3.201 -12.077 63 0.989 43-106 USGS Gambusia holbrooki 3.189 -12.113 198 0.984 10-40 USGS Gobiosoma bosc 2.890 -10.527 150 0.903 11-39 USGS Gobiosoma robustum 3.012 -10.833 486 0.910 8-34 USGS
Jordanella floridae 3.234 -11.505 56 0.971 19-41 USGS 161 Leiostomus xanthurus 3.069 -11.524 108 0.997 39-173 USGS Lucania parva 3.059 -10.884 743 0.900 8-40 USGS Menidia peninsulae 3.035 -12.032 107 0.972 32-98 USGS Microgobius gulosus 3.099 -12.121 174 0.974 17-71 USGS Mugil cephalus 3.114 -11.507 91 0.915 32-52 USGS Paleomonetes pugio 3.052 -11.697 402 0.850 17-38 USGS Paleomonetes pugio (eggs) 2.423 -9.509 225 0.727 21-38 USGS Poecilia latipinna 3.141 -11.519 450 0.990 15-59 USGS Sciaenops ocellatus 2.976 -11.382 30 0.933 286-380 USGS Strongylura notata 3.277 -14.724 37 0.982 71-320 USGS Syngnathus scovelli 3.455 -16.225 162 0.965 25-83 USGS Trinectes maculatus 3.247 -11.897 18 0.955 52-81 USGS
Table 35. Continued
Loge(Wt) = Loge(TL)* a + b No. r Range (mm TL) Reference
Lepisosteus platyrhincus (spring scale) 2.692 -10.293 110 0.8187 370-615 USGS Arius felis (spring scale) 3.081 -12.235 52 0.8506 301-390 USGS Leiostomus xanthurus (spring scale) 3.448 -13.597 31 0.9644 171-321 USGS Mugil cephalus (spring scale) 3.252 -13.042 306 0.9818 105-475 USGS Cynoscion nebulosus (spring scale) 3.084 -12.113 41 0.9580 250-460 USGS
a + b No. r Range (mm) Reference
Caranx hippos Loge(Wt) = Loge(TL)* 3.746 -15.219 27 0.908 95-481 FMRI
Dasyatis sabina Log10(Wt) = Log10(DW,cm)* 3.287 -1.720 388 12 - 36 cm Snelson et al. 1988
Megalops atlanticus Log10(Wt) = Log10(FL)* 2.9156 -7.9156 0.997 106-2045 Crabtree et al. 1995 162 TL = 12.6345 + 1.114 FL Pogonias cromis W = 1.16 X 10-5FL3.05 Murphy and Taylor 1989 TL = -3.8 + 1.03 FL
USGS = Florida Caribbean Science Center, US Geological Survey, 7920 NW 71 St, Gainesville, FL 32653 (fishes collected by Philip Stevens in Banana Creek, Florida - Merritt Island National Wildlife Refuge) FMRI = Florida Marine Research Institute, Florida Fish and Wildlife Convservation Commission, St. Petersburg, Florida.
Snelson, F. F., S. E. Williams-Hooper, and T. H. Schmid. 1988. Reproduction and ecology of the Atlantic stingray, Dasyatis sabina , in Florida coastal lagoons. Copeia 1988: 729-739. Crabtree, R. E., E. C. Cyr, and J. M. Dean. 1995. Age and growth of tarpon, Megalops atlanticus , from South Florida waters. Fishery Bulletin 93: 619-628. Murphy, M. D., and R. G. Taylor. 1989. Reproduction and growth of black drum, Pogonias cromis , in Northeast Florida. Northeast Gulf Science 10: 127-137.
APPENDIX B CORRELATIONS AMONG FISH CATCHES AND WATER CONDITIONS
Table 36. Monthly water conditions and culvert water flow in Impoundment C20C during the study period. Data averaged from continuous hourly readings by datalogger.
Month (2000 - 2001)
Jul Aug Sep Oct Nov Dec* Jan Feb Mar Apr May Jun
Temperature average 31.0 30.8 29.8 24.4 20.8 17.3 15.1 21.8 22.0 25.5 27.6 31.0 (°C) std dev 1.5 1.4 1.6 2.2 3.1 4.2 3.8 2.8 3.0 2.6 2.7 1.7
Salinity average 34.4 31.8 22.0 22.3 27.7 29.5 31.3 32.4 31.9 27.3 29.4 26.9 (ppt) std dev 5.1 1.5 4.2 2.6 1.1 1.5 0.5 1.0 6.6 4.3 4.5 5.7
DO average 1.7 1.5 0.4 1.6 1.7 4.8 3.8 2.7 2.0 2.0 2.0 1.1 164 (mg l-1) std dev 1.8 1.3 0.7 1.2 1.2 1.9 2.1 1.9 1.5 1.7 1.8 1.3
Redox average 123 237 30 461 335 589 439 497 492 392 409 39 (Eh) std dev 243 264 277 243 318 57 49 117 169 224 212 259
Turbidity average 28 23 31 31 19 23 23 19 22 26 25 15 (NTU) std dev 17 23 12 17 10 8 57 29 16 37 19 21
Levelaverage465261675944302735364338 (cm)std dev537669547464
Culvert flow average 11 -3 -20 -22 4 -1 2 1 22 -10 -10 -14 (cm s-1) std dev 27 18 27 15 20 17 11 17 29 11 18 19
* Data for December are from datalogger readings in adjacent Banana Creek due to error in impoundment datalogger.
165
Table 37. Pearson's Correlation among average monthly animal catches and average montly water conditions. Pearson's r values > 0.58 represent alpha < 0.05, and r values > 0.71 represent alpha < 0.01 (r values > 0.58 are shown in bold).
Water Conditions Level Temp. Salinity DO Turbidity Culvert Flow
Water Level Conditions Temperature 0.31
Salinity -0.65 -0.14
DO -0.47 -0.81 0.41
Turbidity 0.52 0.21 -0.40 -0.22
Culvert Flow -0.47 -0.32 0.82 0.32 -0.36
Community Standing Stock -0.58 -0.70 0.31 0.73 -0.16 0.16 Components Net Fish Migration 0.29 0.44 0.26 -0.15 0.37 0.20
Pisc. Fish 0.08 0.57 -0.43 -0.49 0.05 -0.45
Pisc. Birds 0.18 0.26 0.24 -0.10 -0.01 0.01
Standing Stock P. latipinna -0.53 -0.58 0.29 0.59 -0.08 0.11 by Species G. holbrooki -0.42 -0.75 0.25 0.78 -0.10 0.20
C. variegatus -0.74 -0.70 0.34 0.76 -0.29 0.14
M. cephalus -0.59 0.07 0.13 -0.03 -0.65 0.06
M. peninsulae -0.19 -0.61 0.12 0.79 -0.22 0.23
Net Migration P. latipinna 0.11 0.38 0.41 -0.13 0.31 0.33 by Species G. holbrooki 0.04 0.37 0.53 -0.08 0.30 0.36
C. variegatus 0.56 0.44 -0.10 -0.34 0.45 0.05
M. cephalus 0.25 0.76 -0.31 -0.89 0.11 -0.34
M. peninsulae 0.29 -0.01 -0.14 0.25 0.25 -0.41
Pisc. Fish L. platyrhincus -0.11 0.34 -0.47 -0.31 -0.26 -0.54 by Species S. ocellatus 0.40 0.51 -0.17 -0.41 0.55 -0.18
C. nebulosus 0.05 0.36 0.26 -0.29 0.47 0.44
E. saurus 0.39 0.64 0.20 -0.44 0.37 0.10
166
Table 37. Continued
Community Components Standing Stock Net Fish Migration Pisc. Fish Pisc. Birds
Water Level Conditions Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock Components Net Fish Migration -0.42
Pisc. Fish -0.32 0.15
Pisc. Birds -0.06 0.02 -0.17
Standing Stock P. latipinna 0.96 -0.42 -0.37 -0.03 by Species G. holbrooki 0.94 -0.30 -0.26 0.00
C. variegatus 0.92 -0.47 -0.29 -0.16
M. cephalus 0.18 -0.43 0.29 -0.22
M. peninsulae 0.31 -0.06 -0.16 -0.21
Net Migration P. latipinna -0.25 0.96 0.10 0.01 by Species G. holbrooki -0.16 0.88 0.02 0.29
C. variegatus -0.77 0.62 0.00 0.01
M. cephalus -0.65 0.11 0.43 0.03
M. peninsulae 0.24 0.39 0.16 0.19
Pisc. Fish L. platyrhincus -0.12 -0.22 0.88 -0.26 by Species S. ocellatus -0.32 0.48 0.40 0.16
C. nebulosus -0.42 0.61 0.11 0.00
E. saurus -0.45 0.83 0.23 0.41
167
Table 37. Continued
Standing Stock by Species P. latipinna G. holbrooki C. variegatus M. cephalus M. peninsulae
Water Level Conditions Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock Components Net Fish Migration
Pisc. Fish
Pisc. Birds
Standing Stock P. latipinna by Species G. holbrooki 0.85
C. variegatus 0.85 0.82
M. cephalus 0.17 0.04 0.25
M. peninsulae 0.10 0.47 0.34 0.01
Net Migration P. latipinna -0.24 -0.17 -0.31 -0.35 -0.18 by Species G. holbrooki -0.14 -0.08 -0.22 -0.41 -0.22
C. variegatus -0.74 -0.68 -0.78 -0.52 0.01
M. cephalus -0.49 -0.78 -0.59 0.12 -0.82
M. peninsulae 0.20 0.34 0.15 -0.45 0.12
Pisc. Fish L. platyrhincus -0.18 -0.14 -0.03 0.56 -0.06 by Species S. ocellatus -0.29 -0.23 -0.38 -0.48 -0.24
C. nebulosus -0.40 -0.33 -0.46 -0.24 -0.14
E. saurus -0.41 -0.34 -0.55 -0.45 -0.40
168
Table 37. Continued
Net Migration by Species P. latipinna G. holbrooki C. variegatus M. cephalus M. peninsulae
Water Level Conditions Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock Components Net Fish Migration
Pisc. Fish
Pisc. Birds
Standing Stock P. latipinna by Species G. holbrooki
C. variegatus
M. cephalus
M. peninsulae
Net Migration P. latipinna by Species G. holbrooki 0.94
C. variegatus 0.43 0.35
M. cephalus 0.11 0.08 0.26
M. peninsulae 0.34 0.39 -0.09 -0.21
Pisc. Fish L. platyrhincus -0.25 -0.33 -0.30 0.38 0.09 by Species S. ocellatus 0.44 0.44 0.38 0.10 0.28
C. nebulosus 0.63 0.61 0.61 0.21 -0.30
E. saurus 0.84 0.87 0.47 0.29 0.36
169
Table 37. Continued
Pisc. Fish by Species L. platyrhincus S. ocellatus C. nebulosus E. saurus
Water Level Conditions Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock Components Net Fish Migration
Pisc. Fish
Pisc. Birds
Standing Stock P. latipinna by Species G. holbrooki
C. variegatus
M. cephalus
M. peninsulae
Net Migration P. latipinna by Species G. holbrooki
C. variegatus
M. cephalus
M. peninsulae
Pisc. Fish L. platyrhincus by Species S. ocellatus -0.01
C. nebulosus -0.27 0.36
E. saurus -0.18 0.69 0.55
170
Table 38. Spearman's Correlation among average monthly animal catches and average montly water conditions. Spearman's r values > 0.58 represent alpha < 0.05, and r values > 0.71 represent alpha < 0.01 (r values > 0.58 are shown in bold).
Water Conditions Level Temp. Salinity DO Turbidity Culvert Flow
Water Level
Temperature 0.30
Salinity -0.50 -0.15
DO -0.63 -0.77 0.43
Turbidity 0.46 0.20 -0.26 -0.18
Culvert Flow -0.41 -0.37 0.82 0.43 -0.41
Community Standing Stock -0.78 -0.61 0.32 0.87 -0.39 0.24
Net Fish Migration 0.80 0.32 -0.10 -0.32 0.46 -0.18
Pisc. Fish 0.30 0.59 -0.43 -0.51 0.23 -0.43
Pisc. Birds 0.37 -0.10 0.16 -0.07 0.27 -0.03
Standing Stock P. latipinna -0.78 -0.43 0.33 0.74 -0.23 0.19
G. holbrooki -0.79 -0.75 0.36 0.89 -0.47 0.42
C. variegatus -0.80 -0.55 0.20 0.78 -0.41 0.12
M. cephalus -0.75 -0.07 0.14 0.32 -0.56 0.06
M. peninsulae -0.51 -0.71 0.11 0.69 -0.47 0.40
Net Migration P. latipinna 0.69 0.32 0.06 -0.55 0.14 0.11
G. holbrooki 0.00 -0.06 0.46 0.25 0.34 0.26
C. variegatus 0.68 0.05 -0.01 -0.16 0.41 0.09
M. cephalus 0.33 0.71 -0.62 -0.60 0.38 -0.71
M. peninsulae 0.43 -0.16 -0.11 0.04 0.39 -0.09
Pisc. Fish L. platyrhincus -0.07 0.01 -0.70 0.01 0.03 -0.70
S. ocellatus 0.35 0.38 0.20 -0.24 0.36 -0.05
C. nebulosus 0.24 0.43 0.15 -0.27 0.59 0.07
E. saurus 0.74 0.59 -0.08 -0.78 0.27 -0.09
171
Table 38. Continued
Community Components Standing Stock Net Fish Migration Pisc. Fish Pisc. Birds
Water Level
Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock
Net Fish Migration -0.56
Pisc. Fish -0.43 0.36
Pisc. Birds -0.11 0.40 -0.04
Standing Stock P. latipinna 0.91 -0.60 -0.41 -0.17
G. holbrooki 0.94 -0.61 -0.45 -0.19
C. variegatus 0.96 -0.66 -0.33 -0.16
M. cephalus 0.66 -0.72 -0.22 -0.52
M. peninsulae 0.65 -0.38 -0.17 -0.30
Net Migration P. latipinna -0.69 0.71 0.41 0.56
G. holbrooki 0.05 0.31 0.08 0.62
C. variegatus -0.53 0.86 0.15 0.15
M. cephalus -0.52 0.14 0.52 -0.28
M. peninsulae -0.09 0.56 0.32 0.76
Pisc. Fish L. platyrhincus 0.20 -0.19 0.51 -0.15
S. ocellatus -0.31 0.58 0.22 0.31
C. nebulosus -0.48 0.43 0.39 -0.16
E. saurus -0.87 0.63 0.39 0.48
172
Table 38. Continued
Standing Stock by Species P. latipinna G. holbrooki C. variegatus M. cephalus M. peninsulae
Water Level
Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock
Net Fish Migration
Pisc. Fish
Pisc. Birds
Standing Stock P. latipinna
G. holbrooki 0.84
C. variegatus 0.91 0.92
M. cephalus 0.61 0.58 0.64
M. peninsulae 0.38 0.78 0.57 0.45
Net Migration P. latipinna -0.70 -0.61 -0.71 -0.74 -0.39
G. holbrooki 0.11 0.04 0.05 -0.53 -0.19
C. variegatus -0.59 -0.46 -0.67 -0.67 -0.14
M. cephalus -0.43 -0.65 -0.41 -0.08 -0.50
M. peninsulae -0.19 -0.13 -0.15 -0.59 0.00
Pisc. Fish L. platyrhincus 0.16 0.12 0.38 0.17 0.17
S. ocellatus -0.06 -0.37 -0.29 -0.51 -0.63
C. nebulosus -0.32 -0.43 -0.53 -0.33 -0.30
E. saurus -0.79 -0.86 -0.84 -0.73 -0.70
173
Table 38. Continued
Net Migration by Species P. latipinna G. holbrooki C. variegatus M. cephalus M. peninsulae
Water Level
Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock
Net Fish Migration
Pisc. Fish
Pisc. Birds
Standing Stock P. latipinna
G. holbrooki
C. variegatus
M. cephalus
M. peninsulae
Net Migration P. latipinna
G. holbrooki 0.37
C. variegatus 0.60 0.10
M. cephalus -0.08 -0.23 -0.07
M. peninsulae 0.55 0.53 0.40 -0.22
Pisc. Fish L. platyrhincus -0.30 -0.18 -0.36 0.41 0.17
S. ocellatus 0.53 0.45 0.44 -0.08 0.31
C. nebulosus 0.29 0.25 0.48 0.26 -0.05
E. saurus 0.88 0.29 0.45 0.30 0.35
174
Table 38. Continued
Pisc. Fish by Species L. platyrhincus S. ocellatus C. nebulosus E. saurus
Water Level
Temperature
Salinity
DO
Turbidity
Culvert Flow
Community Standing Stock
Net Fish Migration
Pisc. Fish
Pisc. Birds
Standing Stock P. latipinna
G. holbrooki
C. variegatus
M. cephalus
M. peninsulae
Net Migration P. latipinna
G. holbrooki
C. variegatus
M. cephalus
M. peninsulae
Pisc. Fish L. platyrhincus
S. ocellatus -0.19
C. nebulosus -0.35 0.36
E. saurus -0.29 0.48 0.31
APPENDIX C ESTIMATED BIOMASS OF FISH CAPTURED DURING STUDY
Table 39. Biomass of fish (g) captured by cast net on the marsh surface (n = 14 deployments each month).
2000 - 2001
Species Jul Oct Jan Total
Cyprinodon variegatus R 88 112 139 340 Mugil cephalus T 184 29 213 Poecilia latipinna R 44 155 2 201 Fundulus grandis R5454 Lucania parva R718
Menidia peninsulae R6 6 176 Fundulus confluentus R11 Gambusia holbrooki R0.10.21 1 0 Residents - R 132 334 144 610 Transients - T 184 29 213 Total 316 363 144 822
Table 40. Biomass (g) of fish captured by cast net within ditch and creek in Impoundment C20C (n = 28 deployments each month).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Total
Poecilia latipinna R 2 52 5 1 1 177 596 479 77 136 602 36 933 3,099 Cyprinodon variegatus R 3 1 0.3 1 213 454 562 87 266 205 235 353 2,380 Mugil cephalus T 153 124 27 217 589 182 92 140 55 196 136 1,911 Fundulus grandis R 3 168 138 3 43 55 1 143 78 633 Leiostomus xanthurus T 73 49 38 57 218 Gambusia holbrooki R 0.2 0.3 47 121 12 9 6 3 1 2 200 Menidia peninsulae R 2 2 6 31 9 2 15 8 6 17 23 118
Lucania parva R1 1184417310.4591 177 Elops saurus T29 17 46 Anchoa mitchilli I11021124 Fundulus confluentus R 6 2211211024 Palaemonetes pugio R 1 12 14 61 318 Strongylura notata T5 5 515 Jordanella floridae R 22 Microgobius gulosus I2 2
Residents - R 4 61 7 3 9 663 1,364 1,079 235 481 820 433 1,407 6,564 Transients - T 107 207 124 65 217 589 182 92 140 55 270 141 2,189 Incidentals - I 1 2 10 2 11 26 Total 111 268 7 128 75 881 1,963 1,262 329 620 885 703 1,547 8,779
Table 41. Biomass (g) of fish captured by cast net along Banana Creek shoreline adjacent to Impoundment C20C (n = 14 deployments each month).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Total
Cyprinodon variegatus 10 0.1 25 7 2 134 12 14 50 189 442 Poecilia latipinna 26 28 7 61 3 129 117 371 Floridichthys carpio 27 50 6 0.2 24 41 29 55 231 Mugil cephalus 19 23 17 53 2 1 7 63 185 Fundulus grandis 8 89 97 Lucania parva 4 4 1 0.4 6 7 0.4 19 18 2 12 6 79
Anchoa mitchilli 5 2 11 18 178 Palaemonetes pugio 0.2 4 52110.22218 Brevoortia smithi 16 16 Elops saurus 10 10 Menidia peninsulae 617 Eucinostomus argenteus 33 Gambusia holbrooki 20.13 Microgobius gulosus 0.4 0.1 2 2 Sygnathus scovelli 10.1 0.31 2 Cynoscion nebulosus 1 1 Gobiosoma bosc 0.3 0.3 Gobiosoma robustum 0.1 0.1 Hippocampus reidi 0.1 0.1
Total 120 105 8 3 31 94 19 4 188 103 149 230 431 1,485
Table 42. Biomass (g) of small fish (< 150 mm total length) moving out of Impoundment C20C captured by culvert trap.
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs traps fished) (369) (369) (367) (346) (378) (357) (363) (195) (359) (283) (369) (370) (4,124)
Cyprinodon variegatus R 309 334 4 0.4 23 8,223 3,140 233 408 229 7,095 19,998 Poecilia latipinna R 2,693 3,002 73 159 5 57 1,006 307 420 532 542 841 9,636 Leiostomus xanthurus T 388 505 208 5,889 96 11 133 19 358 7,606 Mugil cephalus T 10 788 62 3,554 1,488 16 18 46 71 52 6,105 Menidia peninsulae R 120 14 8 204 2 244 566 371 2,638 186 693 346 5,393 Fundulus grandis R 28 25 32 3,728 28 33 6 23 3,902 Lucania parva T 194 155 39 107 77 728 141 335 24 63 155 2,018
Palaemonetes pugio R 20 49 41 93 21 27 158 96 90 40 67 170 871 179 Callinectes sapidus T 192 331 523 Gambusia holbrooki R73284 150.210332347225245351 Malaclemys terrapin tequesta R 250 250 Trinectes maculatus T 12 124 14 10 160 Alpheus heterochaelis I 17 7 2 1 16 20 97 160 Anchoa mitchilli I5311304254 Cynoscion nebulosus T10284 41 Fundulus confluentus R 11 2 23 1 1 39 Microgobius gulosus I 1 4 4 0.4 3 16 27 Penaeus aztecus I22 22 Gobiosoma robustum I 0.31 32234521 Floridichthys carpio I2 6 3 5 1 17 Gobiosoma bosc I 1 1 51113214 Strongylura notata T2 9 10 Eucinostomus argenteus I16 7
Table 42. Continued
Elops saurus T3 4 7 Arius felis I2 2 Lepomis macrochirus I2 2 Jordanella floridae R11 Hippocampus erectus I11 Sygnathus scovelli I0.3 0.3 Hippocampus reidi I0.1 0.1
Residents - R 3,503 3,454 130 470 29 416 13,715 3,967 3,461 1,193 1,583 8,521 40,440 Transients - T 586 691 1,187 6,027 62 3,737 2,408 157 364 203 484 566 16,470 Incidentals - I 19 3 33 8 7 13 16 35 53 8 11 121 326 Total 4,108 4,149 1,349 6,505 97 4,166 16,138 4,159 3,877 1,404 2,077 9,207 57,236 180
Table 43. Biomass (g) of small fish (< 150 mm total length) moving into Impoundment C20C captured by culvert trap.
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs traps fished) (369) (369) (367) (346) (378) (357) (363) (195) (359) (283) (369) (370) (4,124)
Poecilia latipinna R 6,939 2,620 73 84 7 35 589 79 81 216 66 446 11,234 Cyprinodon variegatus R 1,645 190 3 9 52 1,069 786 177 111 190 480 4,711 Menidia peninsulae R 323 35 33 257 4 511 657 152 852 143 531 166 3,662 Lucania parva R 565 246 46 122 12 212 1,049 193 415 43 63 138 3,105 Mugil cephalus T 495 72 14 762 54 216 9 17 9 131 1,777 Palaemonetes pugio R 40 73 79 191 22 37 299 158 158 123 73 510 1,761 Gambusia holbrooki R212634 22 13482241333829525
Fundulus grandis R 150 15 42 38 10 29 94 16 39 27 459 181 Strongylura notata T84 2 5 91 Trinectes maculatus T4 5347 8 11776 Alpheus heterochaelis I 3 13 8 7 11 8 50 Leiostomus xanthurus T27 119 47 Sciaenops ocellatus T 6 34 40 Gobiosoma robustum I 2 13 224631538 Gobiosoma bosc I 1 3 71463227 Anchoa mitchilli I 2 1 4 11 18 Microgobius gulosus I340.311817 Fundulus confluentus R831 0.42 1 15 Floridichthys carpio I4 2 4 2 12 Chasmodes bosquianus I10 10 Eucinostomus argenteus I2710 Cynoscion nebulosus T2 2 Chilomycterus schoepfi I1 1
Table 43. Continued
Hippocampus erectus I11 Sygnathus scovelli I1 1 Jordanella floridae R0.40.4
Residents - R 9,881 3,244 279 724 54 888 3,806 1,408 1,762 668 988 1,769 25,471 Transients - T 115 8 528 79 16 762 63 222 54 26 9 153 2,033 Incidentals - I 15 3 8 21 6 15 23 3 27 24 6 32 183 Total 10,010 3,255 815 824 77 1,665 3,891 1,632 1,843 718 1,004 1,954 27,687 182
Table 44. Biomass (g) of large fish ( > 150 mm total length) moving in and out of Impoundment C20C captured by culvert trap.
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs traps fished) (369) (369) (367) (346) (378) (357) (363) (195) (359) (283) (369) (370) (4,124)
Egress
Mugil cephalus T 3641 1,809 4,671 3,261 5,365 7,590 5,347 221 1,673 797 650 695 35,718 Leiostomus xanthurus T 1,630 1,395 3,107 136 7,147 283 13,699 Elops saurus T 1362 1,729 3,703 1,664 761.4 152 9,371 Sciaenops ocellatus T 341 1,002 947 2,289
Lepisosteus platyrhincus R 1,873 1,873 183 Cynoscion nebulosus T 143 660 221 1,023 Strongylura notata T 52 7 182 12 252 Dasiatus sabina I94 94
Ingress
Mugil cephalus T 282 204 98 856 280 1720 Elops saurus T 150 99 250 Strongylura notata T22 22
Table 45. Biomass of fish (g) captured by gill net within Impoundment C20C. Piscivorous fishes indicated by asterisk (R = residents, T = transients, I = Incidentals).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs 10 m nets fished) (14) (24) (21) (11) (10) (13) (12) (14) (13) (13) (12) (13) (169)
Lepisosteus platyrhincus* R 1,988 28,515 4,045 1,965 6,662 5,402 5,092 19,042 2,411 43,204 118,327 Sciaenops ocellatus* T 3,033 3,068 10,232 1,186 432 198 18,149 Mugil cephalus T 3,664 2,032 1,623 6,603 977 1,221 749 16,868 Cynoscion nebulosus* T 1,324 1,594 1,766 753 209 3,043 1,078 257 10,024 Elops saurus* T 436 630 618 263 515 50 2,511
Leiostomus xanthurus T 125 85 117 52 173 920 1,473 184 Arius felis I338338
Piscivorous 4,793 7,280 41,130 5,061 2,481 8,057 5,402 5,524 3,043 20,121 2,866 43,253 149,011 Non-piscivorous 3,789 2,032 1,709 6,720 1,029 1,221 338 922 920 18,679 Total 8,581 9,312 42,839 11,781 3,510 9,278 5,402 5,861 3,043 21,043 2,866 44,174 167,689
Table 46. Biomass of fish (g) captured by gill net along Banana Creek shoreline adjacent to Impoundment C20C. Piscivorous fishes indicated by asterisk (R = residents, T = transients, I = Incidentals).
2000 2001
Species Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total N (hrs 10 m nets fished) (14) (24) (21) (11) (10) (13) (12) (14) (13) (13) (12) (13) (169)
Mugil cephalus 771 4,426 12,958 65,396 6,864 1,280 298 1,152 411 1,815 6,263 101,634 Arius felis 2,353 15,906 7,709 4,989 1,634 3,640 266 3,200 2,285 3,581 5,044 50,607 Caranx hippos* 2,363 15,670 2,390 1,601 1,957 23,981 Sciaenops ocellatus* 3,538 3,366 2,746 1,251 3,193 1,227 481 1,942 17,746 Dasyatis sabina 305 708 1,016 4,559 712 7,300
Elops saurus* 1,251 1,165 2,260 1,487 701 258 7,121 185 Pogonias cromis* 5,684 434 6,118 Lepisosteus platyrhincus* 1,098 3,914 560 490 6,062 Cynoscion nebulosus* 1,318 330 1,196 285 261 515 3,904 Leiostomus xanthurus 527 1,349 712 168 710 3,466 Megalops atlanticus* 1,957 888 2,845 Centropomis undecimalis* 565 600 1,165 Micropogonias undulatus 316 316 Sphoeroides nephelus 240 240 Dorosoma cepedianum 191 191 Diapterus auratus 173 173 Bairdiella chrysoura 30 30
Piscivorous 2,569 12,750 9,011 26,899 4,902 3,478 490 1,227 1,601 2,700 3,057 258 68,941 Non-piscivorous 3,123 20,859 20,972 72,615 10,733 5,118 564 1,152 3,440 2,695 10,665 12,019 163,957 Total 5,692 33,609 29,983 99,514 15,635 8,596 1,054 2,380 5,041 5,395 13,722 12,277 232,898
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BIOGRAPHICAL SKETCH
Philip Wesley Stevens was born in Hollywood, Florida, during December of
1973, but soon moved to Gainesville, Florida. His interest in marine science stems from many trips to the coast, and fishing offshore in the Florida Keys and along Florida’s northern shorelines. After graduating from Buchholz High School in 1991, Philip attended Santa Fe Community College before transferring to the University of Florida as a zoology major where he graduated with highest honors. During his undergraduate education, Philip worked at Elite Software as a Customer Service Representative. Philip remained at the University of Florida for his M.S. and Ph.D. degrees in environmental engineering sciences as a Florida Sea Grant-Aylesworth scholar. As a graduate student, he worked at Florida Caribbean Science Center, US Geological Survey, as an
Environmental Scientist. Philip received a Wetlands Certificate from the UF Center for
Wetlands and his M.S. degree, specializing in systems ecology/wetland studies, in May of
1999. He received his Ph.D. in August 2002.
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