Figure 1. (above) Comparison of the fish caught with the roller trawl versus the sock. [larger image]

Figure 2. (above) Comparison of the fish caught with the throw-trap north and south of Black Point and along the western shore of Elliot Key. [larger image]

Loss and (or) degradation of coastal wetlands and nearshore estuarine habitats are long-term threats to ecological function and production of natural resources in Biscayne Bay. Because of its clear, shallow waters, Biscayne Bay's benthic community is a principal source of productivity and diversity. The seagrass/algae associated animal community, consisting of small forage fish, juvenile gamefish, and invertebrates such as pink shrimp, Farfantepenaeus duorarum, is particularly well developed in the shallow nearshore zone adjacent to the mainland and may be dependent upon freshwater inflow. The purpose of this study is to describe the spatial patterns of faunal community composition and species abundance in relation to salinity in the shallow, nearshore habitats of southern Biscayne Bay and ultimately to evaluate the influence of freshwater discharge on community structure.

A random stratified sampling design is being employed to characterize the spatial and temporal patterns of fish and invertebrate community structure in nearshore habitats and to facilitate a throw-trap/commercial roller trawl comparison in the adjacent deeper water commercial fishing zone. At present 54 randomly selected sampling sites, distributed on an areal basis among three salinity strata and an Elliot Key western shoreline control site, are being sampled bi-monthly. The three salinity strata are each subdivided into zones north and south of Black Point, while a subset of these sampling sites in deeper water are associated with the gear comparison.

A 1m² throw-trap suitable for sampling across the full range of water depths observed in Biscayne Bay is being used to collect quantitative samples of fish and macroinvertebrates. A commercial shrimper, using a 4.4 m roller trawl, is sampling in water deeper than 1 m. Throw-trap and roller trawl sampling is coordinated to affect the gear comparison. All fishes and caridean and penaeid shrimp collected are identified, counted and sized as appropriate in the laboratory. Each throw-trap sample is associated with habitat quantitatively using a variety of techniques: visual, quadrat harvest, and Braun Blanquet. An emphasis in this study on coupling habitat (seagrass, algae, hardbottom) with fish and invertebrate community structure recognizes the importance of habitat, particularly seagrass habitat, in organizing benthic communities and to the nursery function of the bay.

Sampling was initiated in the fall of 2002. Preliminary fish results are available characterizing the fish community in southern Biscayne Bay. Similar results are available for caridean shrimp and the pink shrimp. Figure 1 compares fish caught in the roller trawl net enclosed in a smaller mesh net referred to here as a sock. The sock captures fish and shrimp that might otherwise pass through the roller trawl net. Fish abundance in the collections was relatively low with averages/trawl of less than 8 for the most abundant species, Lagodon rhomboides, the pinfish, and the yellowfin mojarra, Gerres cinereus. Figure 2 compares fish caught with the throw-trap. The Elliot Key area serves as a potential control for the western shoreline of Biscayne Bay where changes in salinity patterns due to restoration of freshwater flow are expected. The fish fauna observed in Biscayne Bay is similar to that observed in western Florida Bay with the exception that parrotfish are present but absent in Florida Bay. With the exception that densities are lower the fish community along the western shore of Biscayne Bay, dominated by the rainwater killifish, Lucania parva, is typical of the seagrass associated fish community in Florida Bay.

These results are preliminary. More detailed analyses focusing on evaluating the relationship of fish and invertebrates to salinity and habitat and comparing the throw-trap and roller trawl gears will be presented.

Contact: Kieckbusch, David, USGS, Water and Restoration Studies Center, Miami, FL, 33178, Phone: 305-348-6997, Fax: 305-348-4096, e-mail: david_kieckbusch@usgs.gov

(This abstract was taken from the Greater Everglades Ecosystem Restoration (GEER) Open File Report 03-54)

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