Using Environmental DNA to Detect Bonnethead Sharks in Tampa Bay, FL

Bonnethead sharks (Sphyrna tiburo) are becoming increasingly endangered due to overfishing. Better knowledge of where these sharks tend to travel most within Tampa Bay will create more opportunities for public outreach and conservation methods, such as designing or modifying regulations that could increase shark survival rates from fishing. Previous research on S. tiburo migration has been done using acoustic tagging and catch-and-release methods, but the environmental DNA (eDNA) technique relies on non-invasive detection methods. For this study, water was collected from 12 locations around the bay once per month, along with temperature and salinity. Samples were filtered, and the eDNA was extracted. Quantitative PCR was used to test the environmental samples against a tissue sample from S. tiburo to determine the presence or absence of bonnethead DNA. Bonnethead sharks were detected at the Apollo Beach Preserve in four separate months, which was less successful than expected. In contrast, at sites with visually observed bonnethead sharks, eDNA is almost always detected. This suggests that qPCR alone may not be a sensitive enough technique for the detection of bonnethead sharks. Successful detection within eDNA samples may be more dependent on the proximity of the target species to the sample location, as well as the density of eDNA shed from the organism. More research is needed to determine a more reliable single-species assay useful for environmental DNA sampling of marine vertebrates.

For more information, email: lecarter@eckerd.edu