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
ii 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.
iii 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.
iv TABLE OF CONTENTS ACKNOWLEDGMENTS............................................................................................. ii LIST OF TABLES......................................................................................................... vii LIST OF FIGURES........................................................................................................ x ABSTRACT................................................................................................................... xi v 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 Â– Resident Migrations............................................................................ 12 Hypotheses Â– Trophic Relay by Transients................................................................ 13 2 FIELD METHODS.................................................................................................... 23 Study Area................................................................................................................. . 24 Water Conditions....................................................................................................... 2 6 Fish Standing Stock................................................................................................... 27 Fish Ingress/Egress..................................................................................................... 30 Piscivores................................................................................................................. .. 32 Statistical Analysis..................................................................................................... 33 3 FIELD RESULTS...................................................................................................... 43 Water Conditions....................................................................................................... 4 3 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
v 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
vi BIOGRAPHICAL SKETCH......................................................................................... 195
vii 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......................................................................................................... 6 1 11. Number of small fish moving into Impoundment C20C captured by culvert trap......................................................................................................... 6 3 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
viii 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
ix 37. PearsonÂ’s correlation among average monthly animal catches and average monthly water conditions................................................................................... 165 38. SpearmanÂ’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
x 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
xi 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
xii 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
xiii 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
xiv 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
xv 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 Â· 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 Â· 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.
1 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;
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 Â“hot-spotsÂ” (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 Â“the trophic relayÂ” 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 Â“trophic relayÂ” 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.
5 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 Â· m2Â· yr-1, which represented 5 Â– 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 Â· m-2Â· 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 EastCentral 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).
7 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 Â– Resident Migrations During the seasonal high water period (July Â– 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 Â– 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 Â– 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. Â· 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. Â· m-2, g Â· 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 Â“sinkÂ” 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.
17 Predation Standing StockImmigrationEmigrationProduction Predation Standing StockImmigrationEmigrationProduction Fig. 2. Nekton biomass budget in a saltmarsh impoundment: Production = standing stock / time Â– immigration + emigration + predation
18 Fig. 3. Illustration of Resident Hypothesis 1: As seasonal water level recedes (b), resident fishes are concentrated into subt idal habitats within the marsh (creeks and ditches). Aportion of the resident fish population leaves the impoundment, contributing to the estuary prey base. a) Seasonal High Water (July Â–February) b) Seasonal Low Water (February Â– July). Arrows indicate net direction of travel byfishes.Resident Hypothesis 1a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface DikeResident Hypothesis 1a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface Dike
19 Fig. 4. Illustration of Resident Hypothesis 2: As water level recedes (b), resident fishes are concentrated intosubtidalhabita ts within the marsh (creeks and ditches) and few leave the impoundment. a) Seasonal High Water (July Â–February) b) Seasonal Low Water (February Â–July).Resident Hypothesis 2 a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface DikeResident Hypothesis 2 a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface Dike
20 Fig. 5. Illustration of Juvenile Transient Hypothesis 1: Juvenile transient fishes (small fish shown in Â‘aÂ’) enter the impound ment, grow, (large fish shown in Â‘bÂ’) and some eventually emigrate to the estuary. More biomass may leave than entered (although fewer individuals). a) Seasonal High Water (July Â–February) b) Seasonal Low Water (February Â–July). Arrows indicate net direction of travel by fishes.Juvenile Transient Hypothesis 1a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface DikeJuvenile Transient Hypothesis 1a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface Dike
21 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 Â–February) b) Seasonal Low Water (February Â– July). Small fish in Â‘aÂ’ indicate young fish. Large fish in Â‘bÂ’ indicate fish that have grown.Juvenile Transient Hypothesis 2a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface DikeJuvenile Transient Hypothesis 2a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface Dike
22 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 Â–February) b) Seasonal Low Water (February Â–July). Arrows indicate net direction of travel by fishes. Small fish in Â‘aÂ’ indicate young fish. Large fish in Â‘bÂ’ indicate fish that have grown.Juvenile Transient Hypothesis 3a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface DikeJuvenile Transient Hypothesis 3a b Culvert EstuaryImpoundment Culvert EstuaryImpoundment Ditch Marsh Surface Dike Ditch Marsh Surface Dike
23 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 IslandÂ’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
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, Â“Drainout CreekÂ”, 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 Â– 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 (ÂºC), salinity (Â‰), dissolved oxygen (mg Â· 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 manufacturerÂ’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 Â– 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 ( = 0.05, = 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 ( ! Â· Â½ major axis length Â· Â½ minor axis length). The 14 calculated areas were averaged. Cast net sampling data were reported as fish Â· 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 Â– 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 Â· culvert-1Â· 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 Â– 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 Â– 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 Â– 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 Â· 10 m net-1Â· 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 Â– 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 Â· impoundment-1Â· d-1. Statistical Analysis PearsonÂ’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 PearsonÂ’s correlation, SpearmanÂ’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 TukeyÂ’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 Â· 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.
35 SpeciesCommon NameSpeciesCommon 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 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 ton g uefish Gobiosoma bosc naked goby Syngnathus scovelli gulf pipefish Gobiosoma robustum code goby Trinectes maculatus hogchoker Table 1. Species cited in this study.
36 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 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 Societ y official common names
37 TermDefinition Salt marsh/ImpoundmentDominant 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 estuaryIndian 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 speciesSpecies that complete their life cycle within the salt marsh. Transient speciesSpecies that use salt marshes during some portion of their life cycle either as nursery habitat for young or as regular feeding areas as adults. Incidental speciesSpecies resident to the estuary and occasionally occur in salt marshes by accident, or as a negligable extension of their regular habitat (usually seagrassassociated species). Saltmarsh fishesCollection of resident, transient, and incidental fishes within the salt marsh. Table 2. Terms used to describe various places, habitats, and species.
38 Biomass BudgetGear Type and Habitat ParameterJulAugSepOctNovDecJanFebMarAprMayJunTotal StandingCast net drainout creek141414141414141414141414168 StockCast net perimeter ditch141414141414141414141414168 Cast net estuary shoreline141414141414141414141414168 Cast net marsh surface14141436 Imigration/Culvert trap days4443*444443*4446 EmigrationCulvert trap nights4444444443*4447 Fish PredationGill net drainout creek 11111111111112 Gill net estuary shoreline 22222222222224 Gill net perimeter ditch 33333333333336 Bird PredationMorning bird counts 22222222222224 *Limited b y securit y concerns within NASA ( i.e. , shuttle launches ) Number of De p lo y ments ( 2000 2001 ) Table 3. Summary of monthly gear deployments.
39 Fig. 8. Location of study site (Banana Creek) within the northern Indian River Lagoon system
40 Drainout Creek Impoundment C20A Banana Creek Shuttle Landing Facility Estuary shoreline Vehicle Assembly Building Impoundment C20C Fig. 9. Map of Impoundment C20C within Kennedy Space Center.
41 Dike Road White Mangrove/Brazilian Pepper Cattail Marsh Creek/Ditch Knotgrass Marsh/Shallow Ponds Legend Uplands/High Wetlands F R Datasonde Location Fla pg ated Culvert n Culvert Location Riserboard Culvert Impoundment C20C Banana Creek Drainout Creek Boardwalk to NASA lights Creek Highway 3 Dike Road Impoundment C20A F R F R R R F R F R R 1 3 4 2 Fig. 10. Map of Impoundment C20C showing vegetation types, culvert locations, and datasonde locations.
42 Estuary Drainout Creek Ditch Estuary Ditch Ditch Fig. 11. Gill net deployment locations within Impoundment C20C. Lines indicate orientation of gill nets.
43 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 Â°C, and minimum temperature in winter fell below 10 Â°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 Â‰, and maximum salinities exceeded 40 Â‰. 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 Â· L-1) and redox potential (~400 mV) occurring late in the day,
44 and minimum values (near 0 mg Â· 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 Â– 30 cm Â· 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 Â· 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 (Â± SD) of 14 cast net deployments was 2.8 Â± 0.2 m-2. Catch in each cast net deployment was divided by 2.8 to give abundance or biomass Â· 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 (PearsonÂ’s correlation) among fish standing stock, net fish ingress, piscivorous fish and birds, and average monthly water conditions revealed significant relationships (PearsonÂ’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 (SpearmanÂ’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 SpearmanÂ’s rank correlation, whereas the reverse occurred with PearsonÂ’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 Â· m-2 higher, respectively, than along the shoreline (p = 0.009, 0.0006; TukeyÂ’s pairwise comparisons) (Table 8). Resident fish density by biomass in the creek and the ditch were 5.4 and 3.5 g Â· m-2 higher than along the shoreline (p = 0.003, 0.01; TukeyÂ’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 Â· m-2 higher, respectively, than along the shoreline (p = 0.02, 0.005; TukeyÂ’s pairwise comparisons) (Table 8). For biomass,
48 transient fish density in the ditch was 0.6 g Â· m-2 higher than the creek (p = 0.02) and 0.7 g Â· m-2 higher than the shoreline (p < 0.0001; TukeyÂ’s pairwise comparisons). Transient fish density (g Â· m-2) in the creek was not significantly different from the estuary shoreline (p = 0.08; TukeyÂ’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 Â· culvert-1Â· 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 Â· culvert-1Â· 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 OneWay 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 finclipped 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 Â°C during January 1 and remained cold (< 12 Â°C) for several days. Water temperature again dropped below 12 Â°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 Â· 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 SpeciesJulOctJanTotal Cyprinodon variegatus R4464233341 Poecilia latipinna R3810515158 Mugil cephalus T21223 Lucania parva R527 Gambusia holbrooki R1236 Fundulus grandis R44 Menidia peninsulae R44 Fundulus confluentus R33 0 Residents R83184256523 Transients T21223 Total104186256546 2000 2001 Table 4. Fish (no.) captured by cast net on the marsh surface (n = 14 deployments each month).
56 MonthJulOctJanJulOctJan Residents: Average188.8.131.52.48.53.7 SE1.23.13.00.92.31.0 Transients: Average0.50.14.70.7 SE0.50.14.70.7 Total: Average184.108.40.206.19.23.7 SE1.23.13.04.85.02.0 Biomass (2000 2001) Number (2000 2001) Table 5. Fish Density (fishÂ·m-2 and gÂ·fishÂ·m-2) on the marsh surface.
57 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunJulTotal Poecilia latipinna R2515122451,27732279122579286053,318 Gambusia holbrooki R3545291389772411451,583 Cyprinodon variegatus R421321843630056150121731781,542 Mugil cephalus T11621333385420419728343 Menidia peninsulae R14106613720102814155 Lucania parva R112660193216119 Palaemonetes pugio R5312826202985 Fundulus grandis R115814519650 Fundulus confluentus R3731121422 Anchoa mitchilli I252413 Leiostomus xanthurus T42129 Elops saurus T3 36 Strongylura notata T11 13 Jordanella floridae R 11 Microgobius gulosus I11 Residents R36576241,0372,7227672403357191238276,875 Transients T81406313333854204110229361 Incidentals I000021502040014 Total1179712291,0512,7608052963557642258567,250 20002001 Table 6. Fish (no.) captured by cast net within ditch and creek in Impoundment C20C (n = 28 deployments each month).
58 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunJulTotal Poecilia latipinna 152354829175259 Cyprinodon variegatus 71188260754377228 Floridichthys carpio 143641682030119 Palaemonetes pugio 12222204417687 Lucania parva 581171411210316785 Mugil cephalus 4313114341236 Gambusia holbrooki 2411127 Anchoa mitchilli 33511 Sygnathus scovelli 33129 Menidia peninsulae 448 Fundulus grandis 1 56 Brevoortia smithi 4 4 Microgobius gulosus 1113 Elops saurus 1 1 Cynoscion nebulosus 1 1 Eucinostomus argenteus 11 Gobiosoma bosc 11 Gobiosoma robustum 1 1 Hippocampus reidi 11 Total51719875647251167925186208888 20002001 Table 7. Fish (no.) captured by cast net along Banana Creek shoreline adjacent to Impoundment C20C (n = 14 deployments each month).
59 HabitatCreekDitchShorelineCreekDitchShoreline Residents: Average5.58.01.47.45.52.0 SE220.127.116.11.61.20.5 Statistical groupAABAAB Transients: Average0.30.40.11.13.20.4 SE0.10.10.030.30.90.2 Statistical groupAABBAB Biomass Number Table 8. Comparison of fish density (no. fishÂ·m-2 and g fishÂ·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).
60 HabitatUnmodified TrapReduced Flow TrapUnmodified TrapReduced Flow Trap Average-1.5-4.2-1.01.2 SE18.104.22.168.0 Statistical groupAAAA Biomass Number Table 9. Comparison of fish catch (no. and g fishÂ·trap-1Â·hr-1) between reduced flow and unmodified culvert traps. Values shown are means for each trap type (n = 167 hrs fished for each tra p t yp e ) .
61 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs traps fished)(369)(369)(367)(346)(378)(357)(363)(195)(359)(283)(369)(370)(4,124) Cyprinodon variegatus R25325061244,1451,68288160942,0898,792 Poecilia latipinna R2,9862,341511193627212333524673835508,268 Menidia peninsulae R8710924022933842691,5301513751823,532 Palaemonetes pugio R94187148328591045292702671202485982,952 Lucania parva T232145451357356411323616431091,711 Gambusia holbrooki R17564107712569411044713196840 Mugil cephalus T229416384796715530478 Fundulus grandis R6322193311238 Leiostomus xanthurus T161251062416212175 Alpheus heterochaelis I12331373463 Anchoa mitchilli I328183135 Trinectes maculatus T2243130 Microgobius gulosus I1413111030 Gobiosoma robustum I1264345530 Gobiosoma bosc I11111223223 Cynoscion nebulosus T74112 Fundulus confluentus R5221111 Strongylura notata T16 7 Floridichthys carpio I121217 Eucinostomus argenteus I123 Elops saurus T11 2 Callinectes sapidus T112 Sygnathus scovelli I1 1 20002001 Table 10. Number of small fish (< 150 mm total length) moving out of Impoundment C20C captured by culvert trap.
62 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 R3,6072,857224765655126,0682,4992,3449461,2313,51724,635 Transients T250168107252423964919230747511512,417 Incidentals I1528193921183191052197 Total3,8723,0273391,036727606,7382,7092,6821,0021,2923,72027,249
63 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs traps fished)(369)(369)(367)(346)(378)(357)(363)(195)(359)(283)(369)(370)(4,124) Poecilia latipinna R7,5182,437578453445082932245634611,386 Palaemonetes pugio R168297281765881519924874513602581,7015,999 Cyprinodon variegatus R1,216168630657378228764912703,556 Menidia peninsulae R318393928345436121447071012211293,140 Lucania parva R645280521281422894017833135451032,979 Gambusia holbrooki R45716213753399449263122751,235 Mugil cephalus T3051407663739657288 Fundulus grandis R3047512522664 Gobiosoma robustum I226336841347 Strongylura notata T331337 Gobiosoma bosc I1382654231 Alpheus heterochaelis I28244323 Trinectes maculatus T2210111320 Microgobius gulosus I47111519 Anchoa mitchilli I212712 Leiostomus xanthurus T1629 Fundulus confluentus R3111118 Floridichthys carpio I31217 Eucinostomus argenteus I134 Cynoscion nebulosus T4 4 Sciaenops ocellatus T123 Sygnathus scovelli I11 Jordanella floridae R11 20002001 Table 11. Number of small fish (< 150 mm total length) moving into Impoundment C20C captured by culvert trap.
64 Table 11. Continued Hippocampus erectus I11 Chilomycterus schoepfi I1 1 Chasmodes bosquianus I1 1 Residents R10,3553,3884561,3701121,0563,8371,7601,7638478002,62428,368 Transients T3664062408674541763361 Incidentals I528177141652418823147 Total10,3963,3965041,3931211,1103,8611,8321,8329068152,71028,876
65 Net Fish EgressEgress /Net Fish EgressEgress / SpeciesEgressIngress(egress ingress)IngressEgressIngress(egress ingress)Ingress (no.)(no.)(no.)(g)(g)(g) Cyprinodon variegatus 8,7923,5565,2362.4719,9984,711-15,2874.25 Fundulus grandis 238641743.723,902459-3,4438.51 Menidia peninsulae 3,5323,1403921.125,3933,662-1,7311.47 Fundulus confluentus 11831.383915-232.53 Gambusia holbrooki 8401,235-3950.683515251730.67 Palaemonetes pugio 2,9525,999-3,0470.498711,7618900.49 Lucania parva 1,7112,979-1,2680.572,0183,1051,0870.65 Poecilia latipinna 8,26811,386-3,1180.739,63611,2341,5980.86 Other Fish9055093961.7815,0292,217-12,8126.78 Total27,24928,876-1,6270.9457,23627,687-16,7372.07 NumberBiomass 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).
66 Culvert Location12341234 N (hrs traps fished)(1,079)(991)(1,074)(980)(1,079)(991)(1,074)(980) Residents: Average-22.214.171.124.0-126.96.36.199-3.5 SE188.8.131.52.184.108.40.206.3 Statistical groupAAAABBA BBB Transients: Average-0.10.1-0.2-0.04-3.0-0.3-3.0-1.4 SE0.10.10.10.032.10.51.40.5 Statistical groupAAAAAAAA NumberBiomass Table 13. Comparison of net fish ingress (no. and g fishÂ·culvert-1Â·hr-1) among culvert locations. Values are means of each habitat (pooling months) for the study period; negative values indicate net egress.
67 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs traps fished)(369)(369)(367)(346)(378)(357)(363)(195)(359)(283)(369)(370)(4,124) Egress Mugil cephalus T1232681266571521144229 Leiostomus xanthurus T2821432963193 Elops saurus T222226115288 Strongylura notata T317112 Sciaenops ocellatus T1168 Cynoscion nebulosus T121 4 Lepisosteus platyrhincus R22 Dasiatus sabina I1 1 Ingress Mugil cephalus T9531119 Elops saurus T213 Strongylura notata T3 3 20002001 Table 14. Number of large fish (> 150 mm total length) moving in and out of Impoundment C20C captured by culvert trap.
68 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs 10 m nets fished)(14)(24)(21)(11)(10)(13)(12)(14)(13)(13)(12)(13)(169) Lepisosteus platyrhincus* R3406397630459167 Mugil cephalus T12431633243 Sciaenops ocellatus* T882021140 Cynoscion nebulosus* T9552174134 Elops saurus* T88511124 Leiostomus xanthurus T42211515 Arius felis I11 Piscivorous 252470941277734660265 Non-piscivorous1645184313559 Total4128752781578737665324 20002001 Table 15. Fish (no.) captured by gill net within Impoundment C20C. Piscivorous fishes indicated by asterisk (R = residents, T = transients, I = Incidentals).
69 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs 10 m nets fished)(14)(24)(21)(11)(10)(13)(12)(14)(13)(13)(12)(13)(169) Arius felis 8572416681961013158 Mugil cephalus 192277213131470 Sciaenops ocellatus* 8552511330 Elops saurus* 135441128 Dasyatis sabina 1526216 Cynoscion nebulosus* 31411111 Caranx hippos* 151119 Leiostomus xanthurus 222118 Lepisosteus platyrhincus* 22217 Megalops atlanticus* 123 Centropomis undecimalis* 112 Diapterus auratus 22 Pogonias cromis* 112 Bairdiella chrysoura 11 Dorosoma cepedianum 11 Micropogonias undulatus 11 Sphoeroides nephelus 11 Piscivorous161513246611135192 Non-piscivorous96847321912231072029258 Total2583605625183411102530350 20002001 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).
70 HabitatCreekDitchShorelineCreekDitchShoreline N (hrs 10 m net fished)(89)(80)(173)(89)(80)(173) PiscivorousAverage220.127.116.1128.5998.3341.8 FishSE0.40.30.1253.0205.476.1 Statistical groupAAAAA BB NonPiscivorousAverage0.30.51.5121.2123.2820.7 FishSE0.20.10.362.438.1221.7 Statistical groupAABAAB Biomass Number Table 17. Comparison of piscivorous and nonpiscivorous fish catch (no. and g fishÂ·10 m net-1Â·hr-1) among saltmarsh habitats and estuary shoreline. Values are means of each habitat (pooling months) for the study period.
71 SpeciesNEmptyMisc. Alpheus GrassGobies GambusiaPoeciliaMenidiaC yp rinodon BenthicCrabs AriusLucania FishShrimpInverts Impoundment Sciaenops ocellatus 19924311 Cynoscion nebulosus 111011 Elops saurus 217811221 Lepisosteus 431 platyrhincus Total5529124422221 Shoreline Sciaenops ocellatus 1362114 Elops saurus 227324521 Total351351255421 Fre q uenc y of occurrence ( no. ) Table 18. Stomach contents of piscivorous fish caught in gill nets.
72 SpeciesCommon NameJulAugSepOctNovDecJanFebMarAprMayJunTotal Egretta thula* snowy egret118927322233 Eudocimus albus white ibis49913252234143 Plegadis falcinellus glossy ibis49954112 Hydranassa tricolor* Louisiana heron8482311103413396 waterfowl110342524287 Casmerodius albus* great egret6405712124178 shorebirds141832 Mycteria americana* wood stork6163328 Ajaia ajaja roseate spoonbill10121225 Butorides striatus* green heron4621123423 Ardea herodias* great blue heron32153121321 Megaceryle alcyon* belted kingfisher213232114 Anhinga anhinga* American anhinga1142121113 Dichromanassa rufescens* reddish egret19 10 Himantopus mexicanus black-necked stilt4610 Nycticorax nycticorax* blk.-crowned night heron44 Phalacrocorax auritus* dbl.-crested cormorant1113 Florida caerulea* little blue heron112 Pelecanus occidentalis* brown pelican11 Piscivorous Birds3129716401619621656810526 Non-Piscivorous Birds1421115115135252442134409 Total4531817191311548740982114935 20002001 Table 19. Birds (no.) present within Impoundment C20C during monthly counts (n = 2 counts each month). Piscivorous birds deno ted by asterisk.
73 SpeciesCommon NameJulAugSepOctNovDecJanFebMarAprMayJunTotal Ardea herodias* great blue heron222813119 Eudocimus albus white ibis7714 Hydranassa tricolor* Louisiana heron22318 Mycteria americana* wood stork178 Casmerodius albus* great egret3227 Phalacrocorax auritus* double-crested cormorant167 Pelecanus erythrorhynchos* white pelican44 Pelecanus occidentalis* brown pelican33 Anhinga anhinga* American anhinga22 Butorides striatus* green heron11 2 Pandion haliaetus* osprey 11 Piscivorous Birds841263315161 Non-Piscivorous Birds7714 Total1541263385175 20002001 Table 20. Birds (no.) present along Banana Creek shoreline adjacent to Impoundment C20C during monthly counts (n = 2 counts ea ch month). Piscivorous birds denoted by asterisk.
74 HabitatCreekDitchMarshShorelineCreekDitchMarshShoreline Average2.44.015.52.51,9862,46510,8095,207 SE2.33.538.22.12,1341,78918,4425,143 Statistical groupAAAAAAAA Biomass Number 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).
75 Fig. 12. Water level during 21 months, including study period, from datasondes that continuously measured water conditions hou rly in Impoundment C20C and Banana Creek. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 129-Oct-99 27-Nov-99 26-Dec-99 25-Jan-00 23-Feb-00 23-Mar-00 21-Apr-00 20-May-00 18-Jun-00 18-Jul-00 16-Aug-00 14-Sep-00 13-Oct-00 11-Nov-00 10-Dec-00 9-Jan-01 7-Feb-01 8-Mar-01 6-Apr-01 5-May-01 3-Jun-01 3-Jul-01DateWater Level (m) Banana Creek Impoundment C20C Marsh Elevation Study Period
76 Fig. 13. Water temperature during 21 months, including study period, from datasondes that continuously measured water conditio ns hourly in Impoundment C20C and Banana Creek. 0 5 10 15 20 25 30 35 4029-Oct-99 27-Nov-99 26-Dec-99 25-Jan-00 23-Feb-00 23-Mar-00 21-Apr-00 20-May-00 18-Jun-00 18-Jul-00 16-Aug-00 14-Sep-00 13-Oct-00 11-Nov-00 10-Dec-00 9-Jan-01 7-Feb-01 8-Mar-01 6-Apr-01 5-May-01 3-Jun-01 3-Jul-01DateTemperature (Â°C) Banana Creek Impoundment C20C. Study Period
77 Fig. 14. Diurnal changes in temperature during a typical 10-day period. Summer 2000 0 5 10 15 20 25 30 35 40 5-Jul-006-Jul-007-Jul-008-Jul-009-Jul-0010-Jul-0011-Jul-0012-Jul-0013-Jul-0014-Jul-0015-Jul-00 DateTemperature (Â°C) Banana Creek Impoundment C20C.
78 Fig. 15. Salinity during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek. 0 5 10 15 20 25 30 35 40 45 5029-Oct-99 27-Nov-99 26-Dec-99 25-Jan-00 23-Feb-00 23-Mar-00 21-Apr-00 20-May-00 18-Jun-00 18-Jul-00 16-Aug-00 14-Sep-00 13-Oct-00 11-Nov-00 10-Dec-00 9-Jan-01 7-Feb-01 8-Mar-01 6-Apr-01 5-May-01 3-Jun-01 3-Jul-01DateSalinity (Â‰) Banana Creek Impoundment C20C Study Period
79 Fig. 16. Dissolved oxygen during 21 months, including study period, from datasondes that continuously measured water condition s hourly in Impoundment C20C and Banana Creek. 0 2 4 6 8 10 12 14 16 18 2029-Oct-99 27-Nov-99 26-Dec-99 25-Jan-00 23-Feb-00 23-Mar-00 21-Apr-00 20-May-00 18-Jun-00 18-Jul-00 16-Aug-00 14-Sep-00 13-Oct-00 11-Nov-00 10-Dec-00 9-Jan-01 7-Feb-01 8-Mar-01 6-Apr-01 5-May-01 3-Jun-01 3-Jul-01DateDissolved Oxygen (mg L-1) Banana Creek Impoundment C20C Study Period
80 Fig. 17. Redox potential during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Impoundment C20C and Banana Creek. -400 -200 0 200 400 600 80029-Oct-99 27-Nov-99 26-Dec-99 25-Jan-00 23-Feb-00 23-Mar-00 21-Apr-00 20-May-00 18-Jun-00 18-Jul-00 16-Aug-00 14-Sep-00 13-Oct-00 11-Nov-00 10-Dec-00 9-Jan-01 7-Feb-01 8-Mar-01 6-Apr-01 5-May-01 3-Jun-01 3-Jul-01DateRedox Potential (mV) Banana Creek Impoundment C20C Study Period
81 Fig. 18. Diurnal changes in dissolved oxygen during a typical 10-day period. Summer 2000 0 1 2 3 4 5 6 7 8 9 5-Jul-006-Jul-007-Jul-008-Jul-009-Jul-0010-Jul-0011-Jul-0012-Jul-0013-Jul-0014-Jul-0015-Jul-00 DateDissolved Oxygen (mgÂ·L-1) Banana Creek Impoundment C20C
82 Fig. 19. Diurnal changes in redox potential during a typical 10-day period. Summer 2000 -200 -100 0 100 200 300 400 500 600 5-Jul-006-Jul-007-Jul-008-Jul-009-Jul-0010-Jul-0011-Jul-0012-Jul-0013-Jul-0014-Jul-0015-Jul-00 DateRedox Potential (mV) Banana Creek Impoundment C20C
83 Fig. 20. pH during 21 months, including study period, from datasondes that continuously measured water conditions hourly in Im poundment C20C and Banana Creek. 0 2 4 6 8 10 1229-Oct-99 27-Nov-99 26-Dec-99 25-Jan-00 23-Feb-00 23-Mar-00 21-Apr-00 20-May-00 18-Jun-00 18-Jul-00 16-Aug-00 14-Sep-00 13-Oct-00 11-Nov-00 10-Dec-00 9-Jan-01 7-Feb-01 8-Mar-01 6-Apr-01 5-May-01 3-Jun-01 3-Jul-01DatepH Banana Creek Impoundment C20C Study Period
84 Fig. 21. Diurnal changes in pH during a typical 10-day period. Summer 2000 7.4 7.6 7.8 8 8.2 8.4 8.6 8.8 9 9.2 9.4 5-Jul-006-Jul-007-Jul-008-Jul-009-Jul-0010-Jul-0011-Jul-0012-Jul-0013-Jul-0014-Jul-0015-Jul-00 DatepH Banana Creek Impoundment C20C
85 Fig. 22. Average monthly water flow through Impoundment C20C culverts during study period. Water flow was measured prior to each culvert trap deployment. Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun -50 -40 -30 -20 -10 0 10 20 30 40 50 60 Month (2000 2001)Water Flow through Culverts (cmÂ·s-1) Culvert 1 Culvert 2 Culvert 3 Culvert 4
86 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. 0 1 2 3 4 5 6 JulAugSepOctNovDecJanFebMarAprMayJunNo. Pisciv. FishÂ· 10m Net-1Â·Hr-1 -15 -10 -5 0 5 10 15 20 25Net No. FishÂ·Culvert-1Â·Hr-1 0 10 20 30 40 50 60 JulAugSepOctNovDecJanFebMarAprMayJunJulyNo. FishÂ·m-2 0 50 100 150 200 250 300 JulAugSepOctNovDecJanFebMarAprMayJun Month (2000 2001)No. Pisciv. Birds 0 0.2 0.4 0.6 0.8 1 JulAugSepOctNovDecJanFebMarAprMayJunWater Level (m)d c b a e
87 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. 0 1000 2000 3000 4000 5000 JulAugSepOctNovDecJanFebMarAprMayJung Pisciv. FishÂ· 10m Net-1Â·Hr-1 -45 -35 -25 -15 -5 5 15 25Net g FishÂ·Culvert-1Â·Hr-1 0 5 10 15 20 25 30 35 JulAugSepOctNovDecJanFebMarAprMayJunJulyg FishÂ·m-2 0 40000 80000 120000 JulAugSepOctNovDecJanFebMarAprMayJun Month (2000 2001)g Pisciv. Birds 0 0.2 0.4 0.6 0.8 1 JulAugSepOctNovDecJanFebMarAprMayJunWater Level (m)d c b a e
88 Fig. 25. Number (a) and biomass (b) of the standing stock of resident fishes by habitat. Error bars represent standard error. 0 10 20 30 40 50 60 70 80 90 100 JulAugSepOctNovDecJanFebMarAprMayJunJulyFish density (no.Â·m-2) Ditch Creek Shoreline 0 5 10 15 20 25 30 35 40 45 JulAugSepOctNovDecJanFebMarAprMayJunJuly Month (2000 2001)Fish density (gÂ·m-2) Ditch Creek Shoreline b a Standing Stock by Habitat Resident Fish
89 Fig. 26. Number (a) and biomass (b) of the standing stock of transient fishes by habitat. Error bars represent standard error. b a 0 0.5 1 1.5 2 2.5 3 JulAugSepOctNovDecJanFebMarAprMayJunJulyFish density (no.Â·m-2) Ditch Creek Shoreline 0 5 10 15 20 25 JulAugSepOctNovDecJanFebMarAprMayJunJuly Month (2000 2001)Fish density (gÂ·m-2) Ditch Creek Shoreline Standing Stock by Habitat Transient Fish
90 Fig. 27. Size (mm total length) frequency of Cyprinodon variegatus caught by cast net on the marsh surface at Impoundment C20C. Cyprinodon variegatus Marsh Surface 0 0.1 0.2 0.39-10 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 57-58Total Length (mm)Relative Frequency (%) Jul Oct Jan
91 Fig. 28. Size (mm total length) frequency of Poecilia latipinna caught by cast net on the marsh surface at Impoundment C20C. Poecilia latipinna Marsh Surface0 0.1 0.2 0.39-10 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 55-56Total Length (mm)Relative Frequency (%) Jul Oct Jan
92 Fig. 29. Size (mm total length) frequency of Poecilia latipinna caught by cast net in ditch and creek within Impoundment C20C. Poecilia latipinna Ditch and Creek 0 0.1 0.2 0.39-10 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 69-70Total Length (mm)Relative Frequency (%) Jul-Nov Dec-Feb Mar-May Jun-Jul
93 Fig. 30. Size (mm total length) frequency of Gambusia holbrooki caught by cast net in ditch and creek within Impoundment C20C. Gambusia holbrooki Ditch and Creek 0 0.1 0.2 0.39-10 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 41-42Total Length (mm)Relative Frequency (%) Jul-Nov Dec-Feb Mar-May Jun-Jul
94 Fig. 31. Size (mm total length) frequency of Cyprinodon variegatus caught by cast net in ditch and creek within Impoundment C20C. Cyprinodon variegatus Ditch and Creek 0 0.1 0.2 0.315-16 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 63-64Total Length (mm)Relative Frequency (%) Jul-Nov Dec-Feb Mar-May Jun-Jul
95 Fig. 32. Size (mm total length) frequency of Menidia peninsulae caught by cast net in ditch and creek within Impoundment C20C. Menidia peninsulae Ditch and Creek0 0.1 0.2 0.3 0.46-10 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 96-100Total Length (mm)Relative Frequency (%) Jul-Nov Dec-Feb Mar-May Jun-July
96 Fig. 33. Size (mm total length) frequency of Mugil cephalus caught by cast net in ditch and creek within Impoundment C20C. Mugil cephalus Ditch and Creek 0 0.1 0.2 0.3 0.40-10 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 > 321Total Length (mm)Relative Frequency (%) Jul-Nov Dec-Feb Mar-May Jun -Jul
97 Fig. 34. Size (mm total length) frequency of Lucania parva caught by cast net in ditch and creek within Impoundment C20C. Lucania parva Ditch and Creek 0 0.1 0.2 0.3 0.4 0.5 0.621-22 23-24 25-26 27-28 29-30 31-32 33-34 35-36 37-38 39-40 41-42Total Length (mm)Relative Frequency (%) Jul-Nov Dec-Feb Mar-May Jun-July
98 0 5 10 15 20 25 30 35 JulAugSepOctNovDecJanFebMarAprMayJunNo. Resident FishÂ·Trap-1Â·Hr-1 Ingress Egress 0 5 10 15 20 25 30 35 40 45 50 JulAugSepOctNovDecJanFebMarAprMayJun Month (2000 2001)g Resident FishÂ·Trap-1Â·Hr-1 Ingress Egress a b Fig. 35. Catch rate of resident fish, number (a) and biomass (b), in culvert traps during study period. Ingress and Egress of Resident Fish
99 -40 -30 -20 -10 0 10 20 30 40 50 60No. FishÂ·Culvert-1Â·Hr-1 Culvert 1 Culvert 2 Culvert 3 Culvert 4 b a -100 -80 -60 -40 -20 0 20 40 60 Month (2000 2001)g FishÂ·Culvert-1Â·Hr-1 Culvert 1 Culvert 2 Culvert 3 Culvert 4 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 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. Net Ingress by Culvert Location Resident Fish
100 Fig. 37. Catch rate of transient fish, number (a) and biomass (b), in culvert traps during study period. 0 0.2 0.4 0.6 0.8 1 JulAugSepOctNovDecJanFebMarAprMayJunNo. Transient FishÂ·Trap-1Â·Hr-1 Ingress Egress 0 2 4 6 8 10 12 14 16 18 20 JulAugSepOctNovDecJanFebMarAprMayJun Month (2000 2001)g Transient FishÂ·Trap-1Â·Hr-1 Ingress Egress a b Ingress and Egress of Transient Fish
101 b a -2 -1.5 -1 -0.5 0 0.5 1 1.5No. FishÂ·Culvert-1Â·Hr-1 Culvert 1 Culvert 2 Culvert 3 Culvert 4 Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun -60 -50 -40 -30 -20 -10 0 10 Month (2000 2001)g FishÂ·Culvert-1Â·Hr-1 Culvert 1 Culvert 2 Culvert 3 Culvert 4 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. Net Ingress by Culvert Location Transient Fish
102 Fig. 39. Piscivorous fish catch per unit effort in gill nets, number (a) and biomass (b), by habitat. Error bars represent st andard error. Piscivorous Fish by Habitat b a 0 1 2 3 4 5 6 7 JulAugSepOctNovDecJanFebMarAprMayJunNo. FishÂ·10m Net-1Â·Hr-1 Ditch Creek Shoreline 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 JulAugSepOctNovDecJanFebMarAprMayJun Month (2000 2001)g FishÂ·10m Net-1Â·Hr-1 Ditch Creek Shoreline
103 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. Sciaenops ocellatus 0 2 4 6 8 10 12 14 1626-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500Total Length (mm)Frequency (No.) Culvert Trap Gill Net
104 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. Elops saurus 0 5 10 15 20 2526-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500Total Length (mm)Frequency (No.) Cast Net Culvert Trap Gill Net
105 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. Leiostomus xanthurus 0 20 40 60 80 100 12026-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300Total Length (mm)Frequency (No.) Cast Net Culvert Trap Gill Net
106 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. Cynoscion nebulosus 0 5 10 1526-50 51-75 76-100 101-125 126-150 151-175 176-200 201-225 226-250 251-275 276-300 301-325 326-350 351-375 376-400 401-425 426-450 451-475 476-500Total Length (mm)Frequency (No.) Culvert Trap Gill Net
107 Fig. 44. Number (a) and estimated biomass (b) of piscivorous birds by habitat. Error bars represent standard error. b a 0 5 10 15 20 25 30 35 JulAugSepOctNovDecJanFebMarAprMayJunNo. Pisciv. BirdsÂ·Impound-1 Ditch Creek Marsh Surface Shoreline 143 Â± 124 0 10000 20000 30000 40000 50000 60000 JulAugSepOctNovDecJanFebMarAprMayJun Month (2000 2001)g Pisciv. BirdsÂ·Impound-1 Ditch Creek Marsh Surface Shoreline 76,000 Â± 54,000 Piscivorous Birds by Habitat
108 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
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 Â· ha-1) was less than the average reported for Merritt Island impoundments (0.62 birds Â· 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 Â“sinkÂ” 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.
118 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: 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. P = G Â· B, where: G = (lnw2 lnw1) / " t is the instantaneous coefficient of growth; B = B1(eG-Z 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.
119 Production Estimate from Biomass Budget The fish production estimate derived from RickerÂ’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 Â· 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 Â· 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 Â· 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 birdÂ’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 Â· 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 Â· impoundment-1Â· 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.
123 Standing Stock ! Standing Stock CreekDitchCreekDitchCreekDitch (g fishÂ·im p ound-1Â·mo-1 ) (g fishÂ·im p ound-1Â·mo-1 ) (Â·26,195 m-2)(Â·36,330 m-2) (month2-month1) Jul0.62.215,63781,00126,583137,702164,284199,520 Aug3.43.588,609125,394150,635213,170363,805-353,564 Sep0.00.206,024010,24110,241181,479 Oct0.52.714,16798,61024,083167,637191,720-75,705 Nov0.11.82,07266,1733,522112,493116,0151,175,798 Dec5.616.9147,470612,420250,6991,041,1141,291,8131,601,777 Jan11.638.5302,7631,399,349514,6972,378,8932,893,590-1,181,370 Feb16.016.2419,013588,175712,322999,8981,712,220-1,225,555 Mar2.06.551,588234,68587,700398,965486,665331,841 Apr9.26.6241,719239,755410,922407,583818,506232,533 May20.02.6522,61495,644888,443162,5951,051,038-87,329 Jun8.49.6218,815348,073371,986591,724963,710909,167 July32.86.7859,353242,3391,460,900411,9761,872,876aAssumed to be similar to throw tra p efficienc y ( throw tra p efficienc y ~ 60% ( Jordan et al. 1997 )) Habitat Area Fish Densit y (g fishÂ·m-2)(Â·Gear Efficiencya (1.7)) Po p ulation Biomass Table 22. Estimates of monthly fish standing stock ( " X) within Impoundment C20C (from cast net sampling).
124 MonthNet Fish IngressGear Efficienc y aNet Fish In g ress (g fishÂ·culvert-1Â·hr-1 ) ( Â·24 hr ) ( Â·no. dÂ·mo-1 ) ( Â·8 culverts ) ( Â·6.7 ) = (g fishÂ·im p ound-1 ) Jul15.637492,8502,995622,092 Aug-3.1-75-18,531-598-124,160 Sep0.381,9946613,362 Oct-8.1-195-48,456-1,563-324,654 Nov0.011254835 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 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 Table 23. Estimates of monthly net fish ingress (Med) into Impoundment C20C (from culvert trap sampling). Negative values indicate net egress. 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 No. of gar observed betweenArea between GarAreaArea ofImpoundment culverts 1 and 2culverts 1 and 2densityof ditchDrainout Creekgar population (no.) ( m2 ) ( fishÂ·m-2 ) ( m2 ) ( m2 ) ( no. fish ) 284,1500.00674736,33013,000332 No. of gar caughtNumber of 10 mHrs net lengthsfished deployed 612.3 1132 612.5 712 Total gill net catch per unit effort 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 Gill net catch p er unit effort 2.6 1.8 2.4 3.5 10.3 Table 24. Estimate of Florida gar abundance within the impoundment. Table 25. Conversion from catch per unit effort (no. garÂ· 10 m net-1Â·hr-1) to impoundment gar population.
126 Ageg wet prey consumedÂ· ReferenceSpeciesClass p redator wet bod y wei g ht-1Â·d-1Hunt (1960) Lepisosteus platyrhincus Juvenile0.0281 Hartman and Brandt ( 1995 ) aC y noscion re g alis 10.051 Cynoscion regalis 20.036 Pomatomus saltatrix 00.048 Pomatomus saltatrix 10.043 Pomatomus saltatrix 20.037 McGoo g an and Gatlin ( 1998 ) bSciaeno p s ocellatus Juvenile0.014 0.023 Buckel et al. (1999) Pomatomus saltatrix 00.04 0.12 Hartman (2000) Morone saxatilis 00.0326 0.0559 Average 0.037 0.049 Table 26. Daily prey consumption per predator body weight for selected estuarine fishes. An estimate of 0.04 g prey consumedÂ·d-1 per g body weight predator was used in the model. 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.
127 sum g fishConversion from sum CPUEsum g fish consumedg fish consumedÂ· CPUE-1to Po p ulationaim p ound-1Â·d-1= im p ound-1Â·mo-1 ( Â·30 CPUE im p ound-1 ) ( Â·0.04 ) ( Â·no. dÂ·month-1 ) Jul1,17335,2051,4083143,654 Aug1,20436,1311,4453144,803 Sep9,552286,54611,46230343,855 Oct2,12163,6292,5453178,901 Nov1,27838,3331,5333045,999 Dec3,16694,9813,79931117,776 Jan2,26267,8562,7143184,141 Feb73622,0948842824,745 Mar1,36741,0251,6413150,871 Apr6,962208,8568,35430250,628 May63519,0467623123,617 Jun14,225426,74517,07030512,095 Table 27. Estimates of monthly fish consumption by piscivorous fishes (Yf) within Impoundment C20C. aConversion from gill net catch per unit effort to fish population (Table 26).
128 SpeciesCommon Name WeightaJunorbKushlancWalsbergdBirt-Friesen et al.eAverage (g)(1972)(1978)(1983)(1989) Pelecanus occidentalis* brown pelican3,723596614385632557 Mycteria americana* wood stork2,724436455318504428 Ardea herodias* great blue heron2,588414433309485410 Phalacrocorax auritus* dbl.-crested cormorant1,816291308249375306 Anhinga anhinga* American anhinga1,226196211196282221 Casmerodius albus* great egret908145158163227173 Nycticorax nycticorax* blk.-crown. night heron863138151158218166 Dichromanassa rufescens* reddish egret454738110713799 Hydranassa tricolor* Louisiana heron409657410012792 Egretta thula* snowy egret36358669311683 Florida caerulea* little blue heron36358669311683 Butorides striatus* green heron2273642708358 Megaceryle alcyon* belted kingfisher1362226515739 Consumption (g fishÂ·d-1) Table 28. Daily fish consumption (wet g fishÂ·d-1) by piscivorous birds. The average consumption values for each species were used in the model estimate of prey consumption by piscivorous birds. aWet weight of adult birds (Terres 1980)by = 16% weight of birdÂ·d-1, y = g wet weight preyÂ·d-1 clog y = 0.96 log x 0.64, y = g wet weight preyÂ·d-1, x = weight of bird (g)dln y = ln 12.84 + 0.61 ln (M), y = kJ preyÂ·d-1, M = weight of bird (g)elog y = 2.99 + 0.727 log x, y = kJ energy expenditureÂ·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
129 Avera g e Consum p tionaMonthl y Consum p tion g fishÂ·d-1Â·im p ound-1 ( *no. dÂ·month-1 ) (g fishÂ·mo-1Â·im p ound-1 ) Jul3,25731100,957 Aug14,71931456,292 Sep1,3143039,410 Oct5,66031175,447 Nov1,9173057,515 Dec1,0083131,236 Jan3,84831119,273 Feb1,5162842,454 Mar3883112,036 Apr275308,258 May4213113,058 Jun8683026,046 Table 29. Estimates of monthly fish consumption by birds (Yb) within Impoundment C20C. 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 consumedÂ·impoundment-1Â·month-1.
130 Variables: P = production (A = assimilation, R = respiration) X = impoundment fishes (resident, incidental, and transient fishes) I = ingress E = egress Y = yield to predators O = other disappearance Subscripts : e = estuary d = ditch and creek habitat b = birds f = fish (piscivorous fish only) s = marsh surface Eds Ydb Ydf Od Ysb Ysf Os Ps (=As Rs) Pd (=Ad Rd) Ied Ede Isd Xd Xs " X = change in accumulation x in a finite amount of time ( " t) " Xd = " Xd/ " t = Ied + Pd + Isd Â– Ede Â– Ydb Â– Ydf Â– Eds Â– Od " Xs = " Xs/ " t = Eds + Ps Â– Isd Â– Ysb Â– Ysf Â– Os Net ingress from marsh surface = Msd = Isd Â– Eds Net ingress through culverts = Med = Ied Â– Ede 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. Migrations to and from the marsh surface cancel
131 CHAPTER 6 BIOMASS BUDGET RESULTS Fish production calculated using RickerÂ’s equations was 22.6 g fish Â· m-2Â· 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 Â· m-2 marsh Â· yr-1 (2,388,668 g fish export Â· 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 Â· impoundment-1Â· 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
132 population rather than 3%), then estimated fish production would decrease from 6.800 x 106 to 6.314 x 106 g fish Â· impoundment-1Â· 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 Â· impoundment-1Â· yr-1 (down 12%).
133 MonthFish densityLn (fish density)ZFish densityLn (fish density)GB avgP = GB (no.fishÂ·m-2)(no.fishÂ·m-2)(no.fishÂ·m-2)(gÂ·m-2)(g fishÂ·m-2)(g fishÂ·m-2)(g fishÂ·m-2)(g fishÂ·m-2) Jul0.1-2.02.01.40.18.104.22.168 Aug1.00.0-22.214.171.124-3.71.9-7.1 Sep0.1-126.96.36.199-2.53.00.41.1 Oct0.2-188.8.131.52.5-0.50.9-0.5 Nov0.4-1.03.61.0-0.12.50.61.4 Dec13.42.61.011.22.40.810.48.3 Jan35.23.6-1.225.03.2-0.438.1-16.9 Feb10.32.3-1.016.12.8-1.313.6-18.3 Mar184.108.40.206.220.127.116.11.4 Apr18.104.22.168.22.214.171.124.3 May9.72.3-126.96.36.199-0.219.3-4.5 Jun188.8.131.52.02.20.86.95.4 July10.92.419.73.0 Total Production =22.6 P = GB, where: G = (lnw2 Â– lnw1) / ! t is the instantaneous coefficient of growth; B = B1(eG-Z-1) / (G-Z) is the average biomass; Z = (lnN1 Â– 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 30. Fish production within Impoundment C20C estimated from Ricker's equations.
134 Month ! X YfYbMedP-O Jul199,52043,654100,957622,092-277,961 Aug-353,56444,803456,292-124,160271,691 Sep181,479343,85539,41013,362551,382 Oct-75,70578,901175,447-324,654503,296 Nov1,175,79845,99957,5158351,278,477 Dec1,601,777117,77631,236-239,8821,990,671 Jan-1,181,37084,141119,273-1,008,57230,616 Feb-1,225,55524,74542,454-413,418-744,939 Mar331,84150,87112,036-249,355644,103 Apr232,533250,6288,258-124,027615,445 May-87,32923,61713,058-32,673-17,981 Jun909,167512,09526,046-508,2171,955,524 Total1,708,5921,621,0841,081,981-2,388,668 6,800,326aX = Standing Stock Med = Net Migration from impoundment Yf = Consumption by piscivorous fish O = Other disappearance Yb = Consumption by piscivorous birds g fishÂ·impound-1Â·mo-1 Table 31. Fish production within Impoundment C20C estimated from biomass budget: P O = " X + Yf + Yb Med
135 Input Parameters Changedincrease/Std. ! X YfYbMedP-O % Change in Parameter*decreaseValue(1,708,592)(1,621,084)(1,081,981)-(2,388,668)(6,800,326)P-O Creek densityincr.26 , 195 m-22 , 138 , 8877 , 230 , 6216 decr.1,278,2976,370,030-7 Ditch densityincr.36 , 330 m-21 , 790 , 8746 , 882 , 6081 decr.1,626,3106,718,043-1 Creek areaincr.**2,138,8607,230,5936 decr.1,278,2696,370,003-7 Ditch areaincr.**1,790,8746,882,6081 decr.1,626,3106,718,043-1 Cast net gear efficiencyincr.1.72,221,1707,312,9037 decr.1,196,0146,287,748-8 Net migration CPUEincr.**-3,105,2697,516,92610 decr.-1,672,0686,083,725-12 Culvert trap gear efficiencyincr.6.7-3,105,2697,516,92610 decr.-1,672,0686,083,725-12 Out p ut Characteristics (g marsh-1 mo-1 ) Table 32. Sensitivity analysis of impoundment fish biomass budget.
136 Table 32. Continued Sum gill net CPUEincr.**2,107,4097,286,6517 decr.1,134,7596,314,000-8 Conversion CPUE to Pop.incr.302,107,4097,286,6517 decr.1,134,7596,314,000-8 Daily consump. by fishincr.0.042,107,4097,286,6517 decr.1,134,7596,314,000-8 Bird abundanceincr.**1,406,5767,124,920-5 decr.757,3876,475,7315 Daily consump. by birdsincr.**1,406,5767,124,920-5 decr.757,3876,475,7315 * Parameters were increased and decreased by 30% ** Each month was increased and decreased by 30% to make the adjustment
137 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 Â· 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
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 Â· impoundment-1Â· 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 Â· m-2Â· yr-1 (7.545 x 106 g fish Â· impoundment-1Â· yr-1 / 4.27 x 105 m2Â· impoundment-1). The model based upon RickerÂ’s equations exceeded fish production derived from the biomass budget by 4.9 g fish Â· m-2Â· 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 Â· m-2Â· yr-1 for seagrass fish communities in Mosquito Lagoon, Florida, to well over 30 g fish Â· m-2Â· 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 Â· m-2Â· 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 Â– 27 fish Â· m-2 compared to 7 fish Â· m-2) and turnover (3.0 Â– 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 Â– 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 Â– 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.
141 ! X YfYbMedOP Totals from Table 321,708,5921,621,0841,081,981-2,388,668744,9397,545,265* Percent of production23%21%14%32%10% X = Standing Stock Med = Net Migration from impoundment Yf = Consumption by piscivorous fish O = Other disappearance Yb = Consumption by piscivorous birds g fishÂ·im p ound-1Â·mo-1 Table 33. Estimated fish production incorporating net fish ingress from marsh surface and other disappearance (P = " X + Yf + Yb + O Med). *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 gÂ·yr-1.
142 ReferenceFish communityLocationFish production (g m-2 y r-1 ) Schooley (1980)SeagrassMosquito Lagoon, Florida2.6aHellier (1962), Jones et al. (1963)EstuarineLaguna Madre, Texas12.1 57.6aAdams (1976)SeagrassNorth Carolina18.4aPresent studySalt marshBanana Creek, Florida17.7b , 22.6cYanez-Arancibia and Lara Dominguez (1983)LagoonTerminos Lagoon, Mexico20.0aHolcik (1970)Coastal lagoonCuba22.0 27.6aYanez-Arancibia (1978)Coastal lagoonMexico, Pacific coast24.6 66.7aWarburton (1979)Coastal Mexico, Pacific coast34.5aDay et al. (1973), Wagner (1973)EstuarineBarataria Bay, Louisiana35.0 72.8aAllen (1982)Littoral zone of tidal marshCalifornia37.4aSchooley (1980)Saltmarsh impoundmentsMosquito Lagoon, Florida38.8 59.2a31.5 40.0c 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). a Based on summation of production estimates for component species b Based on fish biomass budget: annual fish production / area of salt marshc 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
143 Fig. 46. Estimated fish production (gÂ· Â· yr-1), water level (m), and marsh elevation (m) in Impoundment C20C during study period. -1000000 -500000 0 500000 1000000 1500000 2000000 2500000Impoundment Fish Production (gÂ·yr-1)0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Water Level and Marsh Elevation (m) Fish Production Water Level Marsh Elevation Fish concentrate into ditch and creek from flooded marsh surface Fish leave ditch for flooded marsh surface Fish leave ditch for flooded marsh surface Other disappearance Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Month (2000 2001)
144 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. Saltmarsh Fishes Large Piscivorous Fishes Avian wildlife 14% (18%) 21% (26%) 32% (39%) Consumption and Migration of Impoundment Fish Production Other Disappearance 10% (12%)
145 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
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 Â‰) 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 Â· m-2 marsh). For perspective, this value exceeds average 1996 Â– 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 Â“hot-spotsÂ” 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 Â· 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 Â“natural marsh settingÂ”. 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 Â“openÂ” 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 Â“naturalÂ” 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.
157 RIM (Rotational Impoundment Management)WAM (Wildlife Aquatic Management) high marshhigh marsh perimeter ditchperimeter ditch dikedike DefinitionDefinition Fig. 48. Management strategies of coastal wetland impoundments in the Indian River Lagoon, Florida. Culverts were installed to manage for mosquito control, while providing exchange of water and aquatic organisms to the estuary when possible. Culverts are closed in the summer, and water is retained on the marsh for mosquito control. Culverts are open fall spring. Water levels are controlled throughout most of the year to encourage wildlife use of saltmarsh by promoting production of vegetation and controlling water levels suitable for a diversity of wildlife. In some impoundments, culverts are opened in spring, and water is allowed to draw down to encourage germination of seed banks. culvert water-control structure marsh la g oon closed: sum. open: fall spring water-control structure marsh la g oon closed: sum. spring o p en: s p rin g sum. culvert
158 Open CulvertBreached marsh marsh high marshhigh marsh perimeter ditchperimeter ditch dike dike lagoon lagoon DefinitionDefinition Fig. 49. Restoration strategies of coastal wetland impoundments in the Indian River Lagoon, Florida. One restoration strategy is to simply leave the culverts open year round to allow water level to fluctuate naturally with the estuary. Culverts are removed and the dike is breached restoring connection between the perimeter ditch and the estuary. However, the breach often fills with sediment, and water circulation becomes restricted culvert
159 Restored (removal of dikes and ditches)Restored Open Water Management (OWM) high marshmarshhigh marshmarsh lagoon lagoon DefinitionDefinition Fig. 49. Continued Rotary ditches connect mosquito "hot spots" to the 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. The dike is pushed back into the perimeter ditch restoring the original elevation of the marsh.
APPENDIX A LENGTH-WEIGHT RELATIONSHIPS FOR FISHES
161 Loge(Wt) =Loge(TL)* a+bNo.rRange (mm TL)Reference Alpheus heterochaelis 3.062-10.825180.96725-55USGS Anchoa mitchilli 2.919-11.256390.95017-66USGS Cynoscion nebulosus 2.885-10.970210.99429-422USGS Cyprinodon variegatus 3.610-12.8553490.99117-52USGS Elops saurus 2.964-11.973420.984159-462USGS Floridichthys carpio 3.385-12.353290.993947-69USGS Fundulus confluentus 3.477-13.063280.99630-71USGS Fundulus grandis 3.201-12.077630.98943-106USGS Gambusia holbrooki 3.189-12.1131980.98410-40USGS Gobiosoma bosc 2.890-10.5271500.90311-39USGS Gobiosoma robustum 3.012-10.8334860.9108-34USGS Jordanella floridae 3.234-11.505560.97119-41USGS Leiostomus xanthurus 3.069-11.5241080.99739-173USGS Lucania parva 3.059-10.8847430.9008-40USGS Menidia peninsulae 3.035-12.0321070.97232-98USGS Microgobius gulosus 3.099-12.1211740.97417-71USGS Mugil cephalus 3.114-11.507910.91532-52USGS Paleomonetes pugio 3.052-11.6974020.85017-38USGS Paleomonetes pugio (eggs) 2.423-9.5092250.72721-38USGS Poecilia latipinna 3.141-11.5194500.99015-59USGS Sciaenops ocellatus 2.976-11.382300.933286-380USGS Strongylura notata 3.277-14.724370.98271-320USGS Syngnathus scovelli 3.455-16.2251620.96525-83USGS Trinectes maculatus 3.247-11.897180.95552-81USGS Table 35. Length-weight relationships for fishes collected within Merritt Island National Wildlife Refuge, Florida.
162 Table 35. Continued Loge(Wt) =Loge(TL)* a+bNo.rRange (mm TL)Reference Lepisosteus platyrhincus (spring scale)2.692-10.2931100.8187370-615USGS Arius felis (spring scale)3.081-12.235520.8506301-390USGS Leiostomus xanthurus (spring scale)3.448-13.597310.9644171-321USGS Mugil cephalus (spring scale)3.252-13.0423060.9818105-475USGS Cynoscion nebulosus (spring scale)3.084-12.113410.9580250-460USGS a+bNo.rRange (mm)Reference Caranx hippos Loge(Wt) = Loge(TL)* 3.746-15.219270.90895-481FMRI Dasyatis sabina Log10(Wt) = Log10(DW,cm)* 3.287-1.72038812 36 cmSnelson et al. 1988 Megalops atlanticus Log10(Wt) = Log10(FL)* 2.9156-7.91560.997106-2045Crabtree et al. 1995 TL = 12.6345 + 1.114 FL Pogonias cromis W = 1.16 X 10-5FL3.05Mur p h y and Ta y lor 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
164 JulAugSepOctNovDec*JanFebMarAprMayJun Temperatureaverage31.030.829.824.420.817.315.121.822.025.527.631.0 (Â°C)std dev184.108.40.206.220.127.116.11.83.02.62.71.7 Salinityaverage34.431.822.022.327.729.531.332.431.927.329.426.9 (ppt)std dev18.104.22.168.22.214.171.124.06.64.34.55.7 DOaverage126.96.36.199.188.8.131.52.72.02.02.01.1 ( m g l-1 ) std dev184.108.40.206.220.127.116.11.18.104.22.168.3 Redoxaverage1232373046133558943949749239240939 (Eh)std dev2432642772433185749117169224212259 Turbidityaverage282331311923231922262515 (NTU)std dev17231217108572916371921 Levelaverage465261675944302735364338 (cm)std dev537669547464 Culvert flowaverage11-3-20-224-12122-10-10-14 ( cm s-1 ) std dev271827152017111729111819 * Data for December are from datalo gg er readin g s in ad j acent Banana Creek due to error in impoundment datalo gg er. Month ( 2000 2001 ) Table 36. Monthly water conditions and culvert water flow in Impoundment C20C during the study period. Data averaged from continuous hourly readings by datalogger.
165 LevelTemp.SalinityDOTurbidityCulvert Flow WaterLevel Conditions Temperature 0.31Salinity -0.65 -0.14DO-0.47 -0.81 0.41Turbidity0.520.21-0.40-0.22Culvert Flow-0.47-0.32 0.82 0.32-0.36CommunityStanding Stock-0.58-0.70 0.31 0.73 -0.160.16Components Net Fish Migration0.290.440.26-0.150.370.20Pisc. Fish0.080.57-0.43-0.490.05-0.45Pisc. Birds0.180.260.24-0.10-0.010.01Standing Stock P. latipinna-0.53 -0.58 0.29 0.59 -0.080.11by Species G. holbrooki -0.42 -0.75 0.25 0.78 -0.100.20C. variegatus-0.74-0.70 0.34 0.76 -0.290.14M. cephalus -0.59 0.070.13-0.03 -0.65 0.06 M. peninsulae-0.19 -0.61 0.12 0.79 -0.220.23Net Migration P. latipinna 0.110.380.41-0.130.310.33by Species G. holbrooki0.040.370.53-0.080.300.36C. variegatus 0.560.44-0.10-0.340.450.05M. cephalus 0.25 0.76 -0.31 -0.89 0.11-0.34M. peninsulae0.29-0.01-0.140.250.25-0.41Pisc. Fish L. platyrhincus-0.110.34-0.47-0.31-0.26-0.54by Species S. ocellatus0.400.51-0.17-0.410.55-0.18C. nebulosus0.050.360.26-0.290.470.44E. saurus0.39 0.64 0.20-0.440.370.10Water Conditions 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).
166 Table 37. Continued Standing StockNet Fish MigrationPisc. FishPisc. Birds WaterLevel Conditions Temperature Salinity DO Turbidity Culvert Flow CommunityStanding Stock Components Net Fish Migration-0.42Pisc. Fish-0.320.15Pisc. Birds-0.060.02-0.17Standing Stock P. latipinna0.96 -0.42-0.37-0.03by Species G. holbrooki 0.94 -0.30-0.260.00C. variegatus0.92 -0.47-0.29-0.16M. cephalus 0.18-0.430.29-0.22 M. peninsulae0.31-0.06-0.16-0.21Net Migration P. latipinna -0.25 0.96 0.100.01by Species G. holbrooki-0.16 0.88 0.020.29C. variegatus -0.770.62 0.000.01M. cephalus -0.65 0.110.430.03M. peninsulae0.240.390.160.19Pisc. Fish L. platyrhincus-0.12-0.22 0.88 -0.26by Species S. ocellatus-0.320.480.400.16C. nebulosus-0.42 0.61 0.110.00E. saurus-0.45 0.83 0.230.41Community Components
167 Table 37. Continued P. latipinnaG. holbrookiC. variegatusM. cephalusM. peninsulae WaterLevel Conditions Temperature Salinity DO Turbidity Culvert Flow CommunityStanding Stock Components Net Fish Migration Pisc. Fish Pisc. Birds Standing Stock P. latipinna by Species G. holbrooki 0.85C. variegatus0.850.82M. cephalus 0.170.040.25 M. peninsulae0.100.470.340.01Net Migration P. latipinna -0.24-0.17-0.31-0.35-0.18by Species G. holbrooki-0.14-0.08-0.22-0.41-0.22C. variegatus -0.74-0.68-0.78 -0.520.01M. cephalus -0.49 -0.78-0.59 0.12 -0.82M. peninsulae0.200.340.15-0.450.12Pisc. Fish L. platyrhincus-0.18-0.14-0.030.56-0.06by Species S. ocellatus-0.29-0.23-0.38-0.48-0.24C. nebulosus-0.40-0.33-0.46-0.24-0.14E. saurus-0.41-0.34-0.55-0.45-0.40Standing Stock by Species
168 Table 37. Continued P. latipinnaG. holbrooki C. variegatus M. cephalus M. p eninsulae WaterLevel Conditions Temperature Salinity DO Turbidity Culvert Flow CommunityStanding 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. holbrooki0.94C. variegatus 0.430.35M. cephalus 0.110.080.26M. peninsulae0.340.39-0.09-0.21Pisc. Fish L. platyrhincus-0.25-0.33-0.300.380.09by Species S. ocellatus0.440.440.380.100.28C. nebulosus0.630.610.61 0.21-0.30E. saurus0.840.87 0.470.290.36Net Migration by Species
169 Table 37. Continued L. platyrhincusS. ocellatusC. nebulosusE. saurus WaterLevel Conditions Temperature Salinity DO Turbidity Culvert Flow CommunityStanding 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-0.01C. nebulosus-0.270.36E. saurus-0.18 0.69 0.55Pisc. Fish by Species
170 LevelTemp.SalinityDOTurbidityCulvert Flow WaterLevel Temperature 0.30Salinity -0.50-0.15DO-0.63-0.77 0.43Turbidity0.460.20-0.26-0.18Culvert Flow-0.41-0.37 0.82 0.43-0.41CommunityStanding Stock-0.78-0.61 0.32 0.87 -0.390.24Net Fish Migration0.80 0.32-0.10-0.320.46-0.18Pisc. Fish0.30 0.59 -0.43-0.510.23-0.43Pisc. Birds0.37-0.100.16-0.070.27-0.03Standing Stock P. latipinna-0.78 -0.430.33 0.74 -0.230.19G. holbrooki -0.79-0.75 0.36 0.89 -0.470.42C. variegatus-0.80 -0.550.20 0.78 -0.410.12M. cephalus -0.75 -0.070.140.32-0.560.06 M. peninsulae-0.51 -0.71 0.11 0.69 -0.470.40Net Migration P. latipinna 0.69 0.320.06-0.550.140.11G. holbrooki0.00-0.060.460.250.340.26C. variegatus 0.68 0.05-0.01-0.160.410.09M. cephalus 0.33 0.71-0.62-0.60 0.38 -0.71M. peninsulae0.43-0.16-0.110.040.39-0.09Pisc. Fish L. platyrhincus-0.070.01 -0.70 0.010.03 -0.70S. ocellatus0.350.380.20-0.240.36-0.05C. nebulosus0.240.430.15-0.27 0.59 0.07E. saurus0.740.59 -0.08 -0.78 0.27-0.09Water Conditions 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).
171 Table 38. Continued Standing StockNet Fish MigrationPisc. FishPisc. Birds WaterLevel Temperature Salinity DO Turbidity Culvert Flow CommunityStanding Stock Net Fish Migration-0.56Pisc. Fish-0.430.36Pisc. Birds-0.110.40-0.04Standing Stock P. latipinna0.91-0.60 -0.41-0.17G. holbrooki 0.94-0.61 -0.45-0.19C. variegatus0.96-0.66 -0.33-0.16M. cephalus 0.66-0.72 -0.22-0.52 M. peninsulae0.65 -0.38-0.17-0.30Net Migration P. latipinna -0.690.71 0.410.56G. holbrooki0.050.310.08 0.62C. variegatus -0.53 0.86 0.150.15M. cephalus -0.520.140.52-0.28M. peninsulae-0.090.560.32 0.76Pisc. Fish L. platyrhincus0.20-0.190.51-0.15S. ocellatus-0.31 0.58 0.220.31C. nebulosus-0.480.430.39-0.16E. saurus-0.870.63 0.390.48Community Components
172 Table 38. Continued P. latipinnaG. holbrookiC. variegatusM. cephalusM. peninsulae WaterLevel Temperature Salinity DO Turbidity Culvert Flow CommunityStanding Stock Net Fish Migration Pisc. Fish Pisc. Birds Standing Stock P. latipinna G. holbrooki 0.84C. variegatus0.910.92M. cephalus 0.610.580.64 M. peninsulae0.38 0.78 0.570.45Net Migration P. latipinna -0.70-0.61-0.71-0.74 -0.39G. holbrooki0.110.040.05-0.53-0.19C. variegatus -0.59 -0.46 -0.67-0.67 -0.14M. cephalus -0.43 -0.65 -0.41-0.08-0.50M. peninsulae-0.19-0.13-0.15 -0.59 0.00Pisc. Fish L. platyrhincus0.160.120.380.170.17S. ocellatus-0.06-0.37-0.29-0.51 -0.63C. nebulosus-0.32-0.43-0.53-0.33-0.30E. saurus-0.79-0.86-0.84-0.73-0.70Standing Stock by Species
173 Table 38. Continued P. latipinnaG. holbrooki C. variegatus M. cephalus M. p eninsulae WaterLevel Temperature Salinity DO Turbidity Culvert Flow CommunityStanding 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. holbrooki0.37C. variegatus 0.60 0.10M. cephalus -0.08-0.23-0.07M. peninsulae0.550.530.40-0.22Pisc. Fish L. platyrhincus-0.30-0.18-0.360.410.17S. ocellatus0.530.450.44-0.080.31C. nebulosus0.290.250.480.26-0.05E. saurus0.88 0.290.450.300.35Net Migration by Species
174 Table 38. Continued L. platyrhincusS. ocellatusC. nebulosusE. saurus WaterLevel Temperature Salinity DO Turbidity Culvert Flow CommunityStanding 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-0.19C. nebulosus-0.350.36E. saurus-0.290.480.31Pisc. Fish by Species
APPENDIX C ESTIMATED BIOMASS OF FISH CAPTURED DURING STUDY
176 SpeciesJulOctJanTotal Cyprinodon variegatus R88112139340 Mugil cephalus T18429213 Poecilia latipinna R441552201 Fundulus grandis R5454 Lucania parva R718 Menidia peninsulae R66 Fundulus confluentus R11 Gambusia holbrooki R0.10.211 0 Residents R132334144610 Transients T18429213 Total316363144822 2000 2001 Table 39. Biomass of fish (g) captured by cast net on the marsh surface (n = 14 deployments each month).
177 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunJulTotal Poecilia latipinna R25251117759647977136602369333,099 Cyprinodon variegatus R310.31213454562872662052353532,380 Mugil cephalus T1531242721758918292140551961361,911 Fundulus grandis R316813834355114378633 Leiostomus xanthurus T73493857218 Gambusia holbrooki R0.20.3471211296312200 Menidia peninsulae R226319215861723118 Lucania parva R11184417310.4591 Elops saurus T29 1746 Anchoa mitchilli I11021124 Fundulus confluentus R62211211024 Palaemonetes pugio R1121461318 Strongylura notata T55 515 Jordanella floridae R 22 Microgobius gulosus I22 Residents R4617396631,3641,0792354818204331,4076,564 Transients T1072071246521758918292140552701412,189 Incidentals I121021126 Total1112687128758811,9631,2623296208857031,5478,779 20002001 Table 40. Biomass (g) of fish captured by cast net within ditch and creek in Impoundment C20C (n = 28 deployments each month).
178 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunJulTotal Cyprinodon variegatus 100.12572134121450189442 Poecilia latipinna 26287613129117371 Floridichthys carpio 275060.224412955231 Mugil cephalus 1923175321763185 Fundulus grandis 8 8997 Lucania parva 4410.4670.41918212679 Anchoa mitchilli 521118 Palaemonetes pugio 0.2452110.22218 Brevoortia smithi 16 16 Elops saurus 10 10 Menidia peninsulae 617 Eucinostomus argenteus 33 Gambusia holbrooki 20.13 Microgobius gulosus 0.40.122 Sygnathus scovelli 10.10.312 Cynoscion nebulosus 1 1 Gobiosoma bosc 0.30.3 Gobiosoma robustum 0.1 0.1 Hippocampus reidi 0.10.1 Total1201058331941941881031492304311,485 20002001 Table 41. Biomass (g) of fish captured by cast net along Banana Creek shoreline adjacent to Impoundment C20C (n = 14 deployments each month).
179 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs traps fished)(369)(369)(367)(346)(378)(357)(363)(195)(359)(283)(369)(370)(4,124) Cyprinodon variegatus R30933440.4238,2233,1402334082297,09519,998 Poecilia latipinna R2,6933,002731595571,0063074205325428419,636 Leiostomus xanthurus T3885052085,8899611133193587,606 Mugil cephalus T10788623,5541,48816184671526,105 Menidia peninsulae R12014820422445663712,6381866933465,393 Fundulus grandis R2825323,72828336233,902 Lucania parva T194155391077772814133524631552,018 Palaemonetes pugio R20494193212715896904067170871 Callinectes sapidus T192331523 Gambusia holbrooki R73284150.210332347225245351 Malaclemys terrapin tequesta R250 250 Trinectes maculatus T121241410160 Alpheus heterochaelis I17721162097160 Anchoa mitchilli I5311304254 Cynoscion nebulosus T1028441 Fundulus confluentus R112231139 Microgobius gulosus I1440.431627 Penaeus aztecus I22 22 Gobiosoma robustum I0.3132234521 Floridichthys carpio I2635117 Gobiosoma bosc I1151113214 Strongylura notata T2910 Eucinostomus argenteus I167 20002001 Table 42. Biomass (g) of small fish (< 150 mm total length) moving out of Impoundment C20C captured by culvert trap.
180 Table 42. Continued Elops saurus T34 7 Arius felis I2 2 Lepomis macrochirus I2 2 Jordanella floridae R11 Hippocampus erectus I11 Sygnathus scovelli I0.30.3 Hippocampus reidi I0.1 0.1 Residents R3,5033,4541304702941613,7153,9673,4611,1931,5838,52140,440 Transients T5866911,1876,027623,7372,40815736420348456616,470 Incidentals I193338713163553811121326 Total4,1084,1491,3496,505974,16616,1384,1593,8771,4042,0779,20757,236
181 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs traps fished)(369)(369)(367)(346)(378)(357)(363)(195)(359)(283)(369)(370)(4,124) Poecilia latipinna R6,9392,620738473558979812166644611,234 Cyprinodon variegatus R1,64519039521,0697861771111904804,711 Menidia peninsulae R323353325745116571528521435311663,662 Lucania parva R56524646122122121,04919341543631383,105 Mugil cephalus T49572147625421691791311,777 Palaemonetes pugio R4073791912237299158158123735101,761 Gambusia holbrooki R2126342213482241333829525 Fundulus grandis R150154238102994163927459 Strongylura notata T842591 Trinectes maculatus T45347811776 Alpheus heterochaelis I3138711850 Leiostomus xanthurus T2711947 Sciaenops ocellatus T63440 Gobiosoma robustum I213224631538 Gobiosoma bosc I1371463227 Anchoa mitchilli I2141118 Microgobius gulosus I340.311817 Fundulus confluentus R8310.42115 Floridichthys carpio I424212 Chasmodes bosquianus I10 10 Eucinostomus argenteus I2710 Cynoscion nebulosus T2 2 Chilomycterus schoepfi I1 1 20002001 Table 43. Biomass (g) of small fish (< 150 mm total length) moving into Impo undment C20C captured by culvert trap.
182 Table 43. Continued Hippocampus erectus I11 Sygnathus scovelli I11 Jordanella floridae R0.40.4 Residents R9,8813,244279724548883,8061,4081,7626689881,76925,471 Transients T1158528791676263222542691532,033 Incidentals I1538216152332724632183 Total10,0103,255815824771,6653,8911,6321,8437181,0041,95427,687
183 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs traps fished)(369)(369)(367)(346)(378)(357)(363)(195)(359)(283)(369)(370)(4,124) Egress Mugil cephalus T36411,8094,6713,2615,3657,5905,3472211,67379765069535,718 Leiostomus xanthurus T1,6301,3953,1071367,14728313,699 Elops saurus T13621,7293,7031,664761.41529,371 Sciaenops ocellatus T3411,0029472,289 Lepisosteus platyrhincus R1,8731,873 Cynoscion nebulosus T1436602211,023 Strongylura notata T52718212252 Dasiatus sabina I94 94 Ingress Mugil cephalus T282204988562801720 Elops saurus T15099250 Strongylura notata T22 22 20002001 Table 44. Biomass (g) of large fish ( > 150 mm total length) moving in and out of Impoundment C20C captured by culvert trap.
184 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs 10 m nets fished)(14)(24)(21)(11)(10)(13)(12)(14)(13)(13)(12)(13)(169) Lepisosteus platyrhincus* R1,98828,5154,0451,9656,6625,4025,09219,0422,41143,204118,327 Sciaenops ocellatus* T3,0333,06810,2321,18643219818,149 Mugil cephalus T3,6642,0321,6236,6039771,22174916,868 Cynoscion nebulosus* T1,3241,5941,7667532093,0431,07825710,024 Elops saurus* T436630618263515502,511 Leiostomus xanthurus T12585117521739201,473 Arius felis I338338 Piscivorous4,7937,28041,1305,0612,4818,0575,4025,5243,04320,1212,86643,253149,011 Non-piscivorous3,7892,0321,7096,7201,0291,22133892292018,679 Total8,5819,31242,83911,7813,5109,2785,4025,8613,04321,0432,86644,174167,689 20002001 Table 45. Biomass of fish (g) captured by gill net within Impoundment C20C. Piscivorous fishes indicated by asterisk (R = res idents, T = transients, I = Incidentals).
185 SpeciesJulAugSepOctNovDecJanFebMarAprMayJunTotal N (hrs 10 m nets fished)(14)(24)(21)(11)(10)(13)(12)(14)(13)(13)(12)(13)(169) Mugil cephalus 7714,42612,95865,3966,8641,2802981,1524111,8156,263101,634 Arius felis 2,35315,9067,7094,9891,6343,6402663,2002,2853,5815,04450,607 Caranx hippos* 2,36315,6702,3901,6011,95723,981 Sciaenops ocellatus* 3,5383,3662,7461,2513,1931,2274811,94217,746 Dasyatis sabina 3057081,0164,5597127,300 Elops saurus* 1,2511,1652,2601,4877012587,121 Pogonias cromis* 5,684434 6,118 Lepisosteus platyrhincus* 1,0983,9145604906,062 Cynoscion nebulosus* 1,3183301,1962852615153,904 Leiostomus xanthurus 5271,3497121687103,466 Megalops atlanticus* 1,957888 2,845 Centropomis undecimalis* 5656001,165 Micropogonias undulatus 316316 Sphoeroides nephelus 240240 Dorosoma cepedianum 191191 Diapterus auratus 173 173 Bairdiella chrysoura 3030 Piscivorous2,56912,7509,01126,8994,9023,4784901,2271,6012,7003,05725868,941 Non-piscivorous3,12320,85920,97272,61510,7335,1185641,1523,4402,69510,66512,019163,957 Total5,69233,60929,98399,51415,6358,5961,0542,3805,0415,39513,72212,277232,898 20002001 Table 46. Biomass of fish (g) captured by gill net along Banana Creek shoreline adjacent to Impoundment C20C. Piscivorous fis hes indicated by asterisk (R = residents, T = transients, I = Incidentals).
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195 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 FloridaÂ’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.