National Shark Research Consortium
Center for Shark Research - Mote Marine Laboratory
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NSRC-supported Initiatives
Shark life history, migration and stock structure
Nearshore-to-offshore (out to approx. 25 miles) fisheries-independent surveys for large coastal sharks will be conducted using MML's 50-foot research vessel, the R/V Eugenie Clark, other MML research vessels, and Florida state research vessels as available. These surveys will be conducted quarterly along the southwest Florida coast from Anna Maria Island to Sanibel Island and will utilize longline and drumline techniques to catch large sharks. In addition, coastal surveys using smaller MML research vessels deploying gillnets and hook-and-line will target juveniles in selected nursery areas, primarily Yankeetown, Florida and in the Florida Keys. These various field surveys are designed to conduct a number of different research procedures, as follows:
Tagging/tracking using conventional, archival and satellite tags: These advanced methods of fish tracking will be used to study seasonal migrations of blacktip (Carcharhinus limbatus), bull (C. leucas) and other large coastal sharks inhabiting the eastern Gulf of Mexico. All live sharks will be tagged with CSR conventional dart tags and/or fin tags (such as rototags) before release; some sharks will be double-tagged with NMFS tags as appropriate for the size of shark. Mature blacktip and bull sharks will be tagged with PAT satellite tags (Wildlife Computers) to investigate the movements of these sharks between winter and summer habitats. Spring surveys will target pregnant blacktips as they approach coastal nursery areas in the eastern Gulf of Mexico. Small archival electronic tags will be attached to neonate and juvenile blacktip sharks at Yankeetown and the Florida Keys to study annual migration patterns between the summer nursery and winter juvenile habitat.
Studies of post-release mortality and short-term movements: These studies will be conducted by fitting selected animals with acoustic transmitters (Vemco V16P transmitters) and tracking their movements after release. These data will be used to help address resource information shortfalls on the impact of NMFS regulations that require fishers to release certain species and sizes of sharks.
Relative abundance studies
Relative abundance of fisheries-relevant coastal shark species in the eastern Gulf of Mexico will be studied using two phases:
Inshore phase: Gillnet surveys by CSR staff in blacktip nursery areas will provide data on the relative abundance of juvenile blacktip sharks, building upon studies originated in 1991. Field trips to two nursery areas in the Florida Gulf (Charlotte Harbor/Pine Island Sound and Yankeetown) will focus on efforts to provide an estimate of relative abundance in these locations. In each area CSR field biologists will conduct two to four quantitative surveys in July-August 2002 and May-June 2003 to assess relative abundance of blacktip shark neonates, young-of-the-year (YOY) and other juveniles in these nurseries. Standardized, random-stratified fishery-independent surveys by gillnet will be conducted in a fashion identical to previous CSR studies of the same areas since 1995. Live sharks will be tagged with CSR dart tags and released, and tissue samples (including genetic samples) will be collected from dead sharks. The purpose of these repeat surveys is to determine if relative abundance of blacktip pups has changed since the 1995-97 surveys, in order to gauge the status of the blacktip stock and results of recent regulations in the shark fishery. Information from these efforts will be analyzed and compared to previous data from these locations to identify any population changes.
Offshore phase: Catch data in fishery independent surveys (1a above) will be analyzed to estimate relative abundance of large animals in the coastal environment. Longline and drumline surveys will be designed to be standardized, random-stratified so that CPUE results in future years will be comparable for the analysis of historical trends. We will confer with our NSRC partner, the VIMS Shark Research Program (Dr. John Musick), to explore the use of gear types and methods identical to theirs, in order to facilitate CPUE comparisons between mid-Atlantic and eastern Gulf shark fauna.
Essential Fish Habitat (EFH) environmental studies
CSR studies of shark nursery areas will be conducted to further our understanding of early life history and critical habitat for juvenile sharks. We will implement new studies of the environmental quality of these essential habitats, beginning with a study of pollutant concentrations and biomarkers of pollutant-mediated effects in juvenile sharks inhabiting nursery areas along the U.S. southeast coast. Because these habitats are often contaminated with environmental pollutants due to coastal development, the physiology of immature sharks, especially the processes that regulate sexual maturation, can be impaired. This study will determine the contaminants present in immature sharks from two commercially important species, the sandbar (Carcharhinus plumbeus) and blacktip shark and investigate if physiological responses to these compounds are present. Sharks will be collected through collaboration with NSRC partners and other on-going studies in Delaware Bay, Chesapeake Bay, Bulls Bay and adjacent barrier islands, and additional sites in North Carolina, Georgia, and the Gulf coast of Florida. Pollutant concentrations will be measured in liver of immature sharks using gas chromatography and mass spectrophotometry. The presence of vitellogenin, a biomarker of animal exposure to estrogenic compounds, will be measured using species-specific antibodies and enzyme-linked immunosorbent assays or other antibody-related procedures. Results will indicate the levels and impacts of these pollutants on the physiology of these juvenile sharks in their nursery areas.
Ecosystem and population modeling
Ecosystem models for shark nursery areas will be developed to examine the importance of juvenile sharks in coastal ecosystems and how changes in the populations of other species may impact shark populations. Models will be based upon ECOPATH and ECOSIM, models developed by ICLARM and the Fisheries Center at the University of British Columbia. Input data for models will include large amounts of information on the diet of sharks collected by previous and new CSR research efforts, as well as data from teleosts and invertebrates studies in the area. Primary target area and species for this modeling effort will be Charlotte Harbor, Florida and the blacktip shark; other models will be developed as warranted, some in conjunction with other NSRC partners. In addition, population assessment of large and small coastal shark species will be conducted in collaboration with Dr. Andre Punt, University of Washington. This work will build upon previous studies to improve assessments of these species in U.S. waters of the Gulf of Mexico and Atlantic Ocean.
Reproductive cycle studies
This research component will involve studies of the reproductive biology of selected species of large, fisheries-relevant sharks. Studies of the shortfin mako shark (Isurus oxyrinchus), conducted in collaboration with Dr. Jose Castro of the NMFS SEFSC, will be conducted to determine the reproductive cycle of the mako shark in the western North Atlantic, by examining mature female specimens caught by commercial and recreational fishermen. Similar studies of Pacific shark species, including species of thresher sharks (Alopias spp.), will be conducted with Dr. Castro in U.S. west coast and Mexican Pacific waters where specimens are available.
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