Assessing Blacktip Shark Population Structure in the Gulf of Mexico with Stable Isotope Analysis.

Binstock, Addie*, John Mohan, University of New England, Biddeford, ME

The Gulf of Mexico (GoM) is home to one of the largest stocks of blacktip sharks. Management has promoted sustainable harvest of blacktips in the GoM, however the IUCN 2020 listed blacktips as vulnerable. The most recent stock assessment manages the entire population of GoM blacktips as one stock, despite evidence suggesting subpopulations of blacktips exist within different regions of the GoM. Due to the socioeconomic importance of GoM blacktips, exploring differences between subpopulations clustered in different regions is critical to ensure the effective management of the species. This study aims to provide the first stable isotope assessment of blacktip shark vertebrae to elucidate the ecological stock structure for these sharks, as well as the underlying physiological processes involved in isotopic assimilation. By comparing isotopic compositions from both the time of capture and time of birth, inferences about diet composition and foraging habitats over an organism’s lifetime can be made. Comparing trends for sharks in different regions will elucidate variations between different subpopulation’s overall habitat use and diet across its constituents’ lifetimes. Understanding differentiation within the GoM blacktip shark population will inform stock assessment efforts to improve management of the Atlantic blacktip shark population in one its most critical habitats.