Understanding shark feeding ecology is of vital importance when developing complete and effective fisheries management strategies for these ecologically important and threatened species. The use of stable isotope analysis (SIA) has the potential to provide increasingly accurate data about shark diet, prey selection, and trophic position that normally is deduced from lethal and potentially biased techniques.
SIA will be used to evaluate the feeding ecology of the blacktip shark, Carcharhinus limbatus, during its seasonal residency in South Carolina waters. Analyzing the ratio of isotope δ 15N in muscle tissue samples will allow trophic position to be estimated. The results obtained will be compared to those that have been estimated based on stomach content analysis.
It is further hypothesized that local blacktips will show evidence of prey switching. If blacktip sharks, normally teleost piscivores, are feeding primarily or in part on seasonally abundant Atlantic sharpnose shark, Rhizoprionodon terraenovae, neonates, we expect them to display a significantly elevated δ15N ratio. The fall migration of blacktips from South Carolinian coastal waters also overlaps with the running and spawning cycles of several teleost fish species. These teleost fish are associated with significantly lower δ15N ratios than sharpnose neonates; therefore blacktips feeding primarily on these teleosts are expected to reflect a similarly reduced δ15N ratio. An ontogenetic shift is also expected between adult and juvenile blacktips.
Sharks will be caught on longlines in North Inlet, a pristine estuary and nursery ground. Sharks will be examined for species, length, and sex and a 5g muscle tissue sample biopsied and stored for analysis. Samples will be lab processed and δ15N ratios will be used to calculate trophic position, and analyzed for evidence for prey switching behavior, and an ontogenetic shift.