Use of the Gulf of Mexico as an overwintering area by western North Atlantic white sharks (Carcharodon carcharias)

Context The white shark (Carcharodon carcharias) is a large, highly migratory, apex predator typically found in coastal, continental shelf and pelagic environments of temperate and subtropical waters worldwide. In the western North Atlantic (WNA), white sharks have been studied for decades through catch data and other observations along the US Atlantic coast. Aims Beginning in 2012, OCEARCH has coordinated a comprehensive, long-term study of this population that includes tagging sharks with satellite-linked and acoustic tags to track their movements, understand their life history, and map their critical habitats. Methods Tagging occurred between Nova Scotia, Canada, and Jacksonville, Florida, USA, on the Atlantic coast. Four life stages (young-of-the-year, juvenile, subadult, adult) were tagged, showing the migratory cycles of this WNA population from age zero through maturity. Key results A combination of satellite-linked and acoustic tags showed all four life stages enter the Gulf of Mexico (GoM) through the Straits of Florida and use this habitat primarily during the overwintering period. Of 92 white sharks tagged, 57 (62.0%) showed activity in the GoM or the Straits of Florida, spending most of their time (91.2%) in epipelagic waters and moving mainly from the Florida Keys north along the outer West Florida Shelf. Specific areas of extensive habitat use and evidence of philopatry were identified, particularly in the Pulley Ridge area off south-western Florida. Some animals crossed into the western GoM and into Mexican coastal waters; movements along the northern coast of Cuba were also noted. Conclusions These tagging results clearly demonstrated the importance of this region as an overwintering habitat for white sharks, particularly in shelf edge waters of the eastern GoM, and indicated a more widespread and persistent use of the GoM by this recovering species than previously known. Implications Our results demonstrated the wide-ranging nature of the WNA white shark population and the faunal connectivity between Atlantic Canada and the GoM, including territorial waters of other nations. Continued monitoring of this population, fine-scale analysis of movements in critical habitats, and further research on the drivers of migration are needed for science-based policy to conserve this vulnerable species.