Certain migratory shark species are staying longer in the Atlantic Ocean's northeast waters before heading south, according to a study led by researchers at Stony Brook University's School of Marine and Atmospheric Sciences (SoMAS). The study tracked six shark species over five years using tagging and acoustic tracking methods.
The findings, published in Conservation Biology, indicate that ocean warming has delayed the southern migration of five shark species by one to 29 days. This delay could impact conservation strategies and ecosystem balance within the Atlantic Ocean.
Maria Manz, a SoMAS PhD student and lead author of the study, said: “Both temperature and photoperiod (length of sunlight) influenced the timing of the sharks’ southernly migration, and it is likely that they both cumulatively influence migratory patterns.” Manz's research focuses on shark ecology in the Northeast Atlantic and New York Bight.
The study showed sea surface temperatures (SST) and photoperiod as strong predictors of migration from 2018 to 2022. Sandbar sharks had the greatest predicted delay with a median delay of 29 days. In contrast, sand tiger and white sharks had only a one-day median delay under projected future SST scenarios.
Researchers defined "southern migration" as each shark's last annual detection within a latitudinal movement region along the Atlantic shelf. They categorized movements into five specific ocean regions along the east coast. Data were collected from 155 sharks, including blacktip, dusky, sand tiger, sandbar, thresher, and white sharks.
These highly migratory species travel annually from northern parts of the west Atlantic to their southern habitats as weather cools down in September or October. Acoustic tagging was used for tracking; this method involves tags with unique IDs for each shark detected by acoustic receivers on the sea floor when sharks come into range.
Manz developed mathematical models using detection data to predict shark movements and identify influential environmental variables driving their southward migration. The authors noted: “Results of the models suggested that projected increases in SST across decades may delay southern autumn migrations of coastal sharks with many species remaining in northern habitats for longer durations.”
The research received support from the New York State Department of Environmental Conservation (DEC) and was conducted under permits granted by DEC, National Oceanographic and Atmospheric Administration, and New Jersey Department of Environmental Protection.