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Certain migratory species of sharks may remain swimming and feeding in Atlantic Ocean waters in areas of the northeast coast for longer periods of time later into fall before they head toward southern waters. Led by researchers in the School of Marine and Atmospheric Sciences (SoMAS) at Stony Brook University, the study tracked six shark species over five years by way of tagging them and acoustically tracking their movement.

The findings, in a paper in Conservation Biology, showed that ocean warming delayed five shark species' southern migrations by anywhere from one to 29 days. Such delays, the scientists say, may affect both conservation strategies for sharks, as well as the balance of ecosystems within the Atlantic Ocean.

The research team consisted of lead author, SoMAS Ph.D. student Maria Manz, along with SoMAS colleagues and co-authors graduate advisor Professor Michael Frisk, Professor Robert Cerrato, Assistant Professor Oliver Shipley, and collaborating scientists based on the east coast.

"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," says Manz, whose research focuses on the ecology of sharks in the Northeast Atlantic and New York Bight, a large triangular region of the Atlantic Ocean.

"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 adds.

Sea surface temperatures (SST) and photoperiod were strong predictors of migration over the five-year period (2018 to 2022). By species, sandbar sharks had the greatest predicted delay with a median delay of 29 days, whereas sand tiger and white sharks had the lowest median delay, by only one day under projected future SST scenarios.

The team defined "southern migration" as the last annual detection for each shark within a latitudinal movement region along the Atlantic shelf. They categorized movement into five specific ocean regions all along the east coast.

Tracking method

Tracking data were incorporated from 155 sharks including blacktip, dusky, sand tiger, sandbar, thresher, and white sharks.

All these sharks are highly migratory species that embark on annual migrations from the northern portions of west Atlantic (the lower Northeast to Canada), then as the weather cools down in September or October they swim to their southern habitats (Carolinas down to Florida).

Manz and colleagues acoustically tracked each of the shark species. Acoustic tagging is a passive form of tracking that has two parts鈥攖he tags themselves, which have a unique identification for each shark and date-time stamp; and the acoustic receivers which constantly detect the tags from the sea floor when the sharks come into range (~900 m).

Using that detection data, Manz developed mathematical models to predict the movement of each of the shark species and to identify which environmental variables are the most influential drivers of their migration south.

Overall, the authors write this about the five-year assessment of the sharks' migratory patterns: "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. Our findings are consistent with previous work showing that both temperature and photoperiod govern shark migratory timing."