LB 4-25 - Investigating Dietary Overlap in Juvenile Bull (Carcharhinus leucas) and Lemon (Negaprion brevirostris) Sharks with DNA Metabarcoding from Cloacal Swabs

Background/Question/Methods:

The Ten Thousand Islands estuary is located downstream of the ongoing Picayune Strand Restoration Project (PSRP). Previous construction in the area dramatically altered the conditions of the estuary. The resulting salinity gradient creates a unique landscape which may influence the distribution of coastal shark species that use the estuary as a nursery area. Multiple species often share the same nursery areas, and therefore experience some level of interspecific competition. Juvenile bull sharks (Carcharhinus leucas) and lemon sharks (Negaprion brevirostris) share the Ten Thousand Islands nursery area. Completion of the PSRP may allow for the expansion of lemon shark distribution. The goal of this study is to identify whether these two species are feeding on the same prey and whether they act as predators to each other. We used DNA barcoding of fecal samples obtained via cloacal swabbing to identify specific prey species. This method involves inserting a sterilized cotton swab into the cloaca of the shark, the swab retrieves DNA of prey that has passed completely through the digestive system that might be missed in stomach flushing. The cloacal swabs were analyzed using the mitochondrial 12S ribosomal RNA region (~171 base pairs) to amplify teleost prey species DNA.

Results/Conclusions:

Twenty juvenile bull sharks and thirteen juvenile lemon sharks were swabbed. Of the thirty-three individuals swabbed twenty-eight (80%) came back with prey DNA. The most common species consumed by juvenile bull sharks was Mugil cephalus (n=10). The most common species consumed by juvenile lemon sharks was Arius felis (n=5). There were seven shared prey species between the two: Mugil cephalus, Arius felis, Elops saurus, Bagre marinus, Mugil curema, Carcharhinus limbatus and Sphyrna tiburo. There was no evidence that these the lemon and bull sharks were consuming each other, however evidence shows both were consuming other shark species: the bonnethead shark (Sphyrna tiburo) and the blacktip shark (Carcharhinus limbatus). These preliminary results suggest the two species feed on similar prey; combined with additional data on the distribution and habitat use of bull and lemon sharks in the Ten Thousand Islands this study will allow us to gain a better understanding of how these two species will respond to the completion of the PSRP.