Using Chemical Tracers to Assess the Population Connectivity of Blacktip Sharks (Carcharhinus limbatus) in the Northern Gulf of Mexico.

Hayne, Abigail H.P.¹*, Travis M. Richards², Nathan R. Miller², Marcus Drymon³, Brett Falterman⁴, R.J. David Wells², John A. Mohan¹, ¹The University of New England, Biddeford, ME, ²Texas A&M, Galveston, TX, ³Mississippi State University, Starkville, MS, ⁴Louisiana Department of Wildlife and Fisheries

Understanding the spatial connectivity of shark populations is critical for regional fisheries management. While conventional and electronic tags have provided valuable information on movement patterns, natural chemical tracers (i.e., trace elements) found in vertebrae offer a more continuous record of life history from birth to death and have been increasingly helpful in studies of migration and connectivity in sharks. The blacktip shark (Carcharhinus limbatus) is a species of interest in the Gulf of Mexico (GoM) due to its migratory life history patterns and importance in recreational and commercial fisheries. However, uncertainty exists in regard to life history and stock structure of blacktip sharks. Genetic studies support stock separation between GoM and the western Atlantic Ocean, and the most recent stock assessment recommended treating blacktip sharks in the eastern and western GoM as separate stocks divided at 88°N as tagging studies show little to no movement between these two regions. Given the importance of this species and the highlighted need for a comparative study of life history across multiple geographic regions of the GoM, the goal of this study was to analyze natal and edge signatures of blacktip shark vertebrae using multi-element (Mn, Ba, Zn, Sr, Mg and Cu) signatures from individuals (n=117) collected from the western (TX), central (LA, MS) and eastern (FL) GoM. This study increases our understanding of the ecological stock structure of blacktip sharks and will help inform future stock assessment models of blacktip shark populations.