Certain migratory shark species may extend their stay in the Atlantic Ocean’s northeast coastal waters longer into the fall before heading south, according to a study by Stony Brook University’s School of Marine and Atmospheric Sciences (SoMAS). Researchers tracked six shark species over five years using tagging and acoustic tracking methods.
The study, published in Conservation Biology, found that ocean warming has delayed the southern migration of five shark species by one to 29 days. These delays could impact conservation strategies for sharks and the balance of ecosystems within the Atlantic Ocean.
Maria Manz, a SoMAS PhD student and lead author of the study, explained that both temperature and photoperiod influence the timing of sharks’ southern migration. “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,” said Manz. Her research focuses on shark ecology in the Northeast Atlantic and New York Bight.
“Our model predictions of migratory timing under future ocean temperatures suggest that species will delay the initiation of their southern migratory timing. We also found both regional and species variation in the predicted delay in shark migratory timing,” she added.
The research indicated that sea surface temperatures (SST) and photoperiod were strong predictors of migration between 2018 to 2022. Sandbar sharks showed a median delay of 29 days, while sand tiger and white sharks had only a one-day median delay under projected 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 regions along the east coast. The team incorporated tracking data from 155 blacktip, dusky, sand tiger, sandbar, thresher, and white sharks.
These highly migratory species travel annually from northern West Atlantic areas to their southern habitats as temperatures cool down around September or October. Acoustic tagging was used to track each shark species passively through tags with unique identification numbers detected by receivers on the sea floor when sharks came within range.
Manz developed mathematical models using detection data to predict each shark species’ movement patterns and identify influential environmental variables affecting their southward migrations.
The authors concluded: “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.” Their findings align with previous studies showing temperature and photoperiod govern shark migratory timing.
This research received support from various agencies including New York State Department of Environmental Conservation (DEC), National Oceanographic & Atmospheric Administration (NOAA), New Jersey Department Environmental Protection (NJDEP).
