The overall strategy is to collect robust empirical field data on forage fish distribution and abundance that can serve multiple purposes: as performance measures in restoration assessment; as the beginning of a long-term dataset analogous to three very powerful datasets from other locales in the Greater Everglades Ecosystem: 15-20 yr from freshwater marshes, 10 yr from the mangrove ecotone of Taylor Slough and adjacent tidal creeks, and 10-12 yr from Florida Bay; and contribute to the basic ecological understanding of mangrove-associated fishes.
Concern about the fate of mangrove ecosystems derives from their known use as habitat for a wide range of aquatic animal species, especially fishes and decapod crustaceans of forage as well as of commercial and recreational importance. Additionally, in South Florida, mangroves on Cape Sable support a seemingly healthy population of diamondback terrapins, a species at risk in many salt marsh environments on the Gulf and Atlantic coasts.
This project is being undertaken to:
(1) determine what fish species make routine use of flooded fringing mangrove forests along the tidal portion of the major drainage of the historical Everglades, i.e., Shark River, and to develop empirical relationships that link species composition, density and biomass to environmental variables at those sites; (2) describe the population structure of a species of special concern, the diamondback terrapin, in mangrove tidal creek habitat within the complex of creeks that make up Big Sable Creek on Cape Sable, and secondarily to determine how this population is related to other populations on the Atlantic and Gulf coasts via DNA analysis; (3) experimentally determine via field and lab experiments the preferred habitat of a species of special concern but a common fish along the Shark River salinity gradient, mangrove rivulus; (4) determine the fisheries impact of the hurricane-induced conversion of mangrove forests to intertidal mudflats in the Big Sable Creek complex.
U.S. Department of Agriculture - Natural Resources Conservation Service (NRCS) Department of the Interior - U.S. Geological Survey Department of Commerce - National Oceanic and Atmospheric Administration (NOAA) Environmental Protection Agency (EPA) Smithsonian Institution - National Museum of Natural History (NMNH)
In addition to taking standard morphometric measurements on each turtle and recording a GPS location for each capture and recapture location, we marked each newly captured terrapin in four ways: (1) by notching the marginal scutes in a systematic pattern, (2) by inserting an individually numbered 9-or 10-digit alpha-numeric passively induced transponder (PIT) tag, (3) by taking head-on, dorsal, ventral, and side view photographs for photo-id (with particular emphasis on capturing the unique pattern of each turtle’s plastron), and (4) by taking blood samples to be screened for microsatellite DNA markers which resulted in locus-specific scores for each individual. For consistency, K. Hart performed all the notching, PIT tagging, photographing, and blood sampling throughout the study. We used the redundant marking system to ensure no tag loss or errors in identification. We also used strict, consistent protocols to catalog animals so that the possibility of misidentification would be essentially zero. We re-weighed and re-measured recaptured turtles, and released all new turtles after workup at their original capture site and all recaptured turtles at their recapture location. Additionally, we attached radiotransmitters to a subset of females to conduct short-term tracking in the study site. For analyses, we constructed a unique 5-capture history for each of the 300 terrapins from the capture and recapture data collected on each trip. Each capture history consisted of the seen (1) or not seen (0) record of the individual during each of the five sampling periods. We used Program MARK and AIC model selection procedures to derive estimates of survival and capture probability. We used Program JOLLY to estimate abundance.
We marked a total of 300 terrapins. We captured 24 animals in crab pots on the first sampling trip (November 2001), but thereafter captured terrapins only with dip nets.
1. We continued to describe fish community structure in fringing mangrove forests along a salinity gradient in Shark River based on periodic field sampling at 3 sites along a longitudinal salinity gradient. We used 9 total 2x3 m2 bottomless lift nets, and 9 total 1x1.5 m2 intertidal rivulet nets. Quantitative estimates of recovery of marked fishes of 2 common species were completed for the lift nets. By the end of FY2004 we will have estimates of discharge from all 9 intertidal rivulet sites. From these data we can thus standardize all capture data to fish per cubic meter at these latter nets.
2. We continued to define population structure and genetics of diamondback terrapins at Big Sable Creek complex immediately south of Shark River. Terrapins have been captured with dip nets on 6 weeklong trips between 11/01 and 10/03. A total of 300 unique individuals with a male: female sex ratio of 1.16:1.0 have been captured, measured, weighed, PIT tagged and had blood drawn for genetic samples. Initial population size estimate is about 1,415 individuals based on the Schnabel method. We estimated downed log cover in 6 headwater creeks to correlate with terrapin capture locations. Final objectives are to refine this population estimate, better characterize habitat use, and finish analysis of blood samples previously collected for DNA characterization.
3. We continued analysis of effects on fisheries of hurricane-induced habitat conversion of mangroves to mudflats at Big Sable Creek complex. Due to destruction from passage of two category 4/5 hurricanes (1935, 1960), some mangroves at Big Sable Creek complex did not recover. Rather, they were converted to intertidal mudflats. This task addresses the fisheries consequence of this storm-induced habitat conversion. The objective is to compare on a quantitative basis the fish species composition, density and biomass in replicate habitats of the two types. We currently have 9 complete sets of samples. We must still make discharge measurements to standardize our catch data to fish per cubic meter of water.
4. Status of the data: Shark River fishes 4.5 years, Big Sable Creek fishes 1.5 years, terrapins 2.5 years, Submerged Aquatic Vegetation (SAV) in Shark River 1 year. Data collection and data entry has been completed for the project. Data analysis and interpretation is ongoing.
U.S. Department of the Interior, U.S. Geological Survey
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