Warming oceans are changing shark migration patterns

As oceans heat up, coastal sharks are adjusting their calendars. Instead of swimming south in early fall, many are now sticking around longer due to global warming.

Researchers at Stony Brook University tracked this trend by following six shark species along the U.S. East Coast. They used acoustic tags and detection models to uncover how ocean warming delays the sharks’ southern migrations by up to 29 days.

“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 lead author Maria Manz.

Sharks delay migration due to warming

The study observed blacktip, dusky, sand tiger, sandbar, thresher, and white sharks. Among them, sandbar sharks showed the longest delay of up to 29 days. They also used the widest range of latitudinal zones, from the New England Shelf to Florida.

White sharks, by contrast, showed the least delay. Being partially warm-bodied (regional endotherms), they are less dependent on external temperature shifts. Their migration changed by only one day under future climate scenarios.

East Coast is warming fast

The study focused on the Mid-Atlantic Bight. This region, especially the New York Bight and New England Shelf, is heating faster than many other parts of the Atlantic.

According to projections based on the high-emissions SSP5 8.5 scenario, the New England Shelf could warm by over 2°C (3.6°F) by 2049.

This rise in temperature affects not just the water, but everything in it. Fish prey species may move earlier or later, altering food availability for predators like sharks.

“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,” wrote the researchers.

How sharks were tracked in warming waters

The researchers tagged 155 sharks and monitored their movements using over 390 acoustic receivers. These receivers picked up signals from the tags whenever sharks came within 900 meters (2,953 feet).

The sharks’ migrations were tracked across five defined zones: New England Shelf (NES), New York Bight (NYB), Mid-Atlantic (MA), Southern Atlantic (SA) and Florida (FL).

Some species, like sandbar and thresher sharks, appeared in all zones. Others, like white sharks, showed more restricted ranges.

Predictors of migration timing

To understand what drives sharks to migrate, the researchers fed their data into mixed-effect Cox models.

The team tested sea surface temperature (SST), photoperiod, and lunar phase. Photoperiod emerged as a consistently strong predictor, especially for thresher sharks.

Interestingly, lunar phase had less influence than expected. Only sandbar sharks showed some sensitivity to moonlight patterns.

Most migration timing was better explained by combinations of light and temperature, which can vary regionally.

Warming delays and shark survival

If sharks delay migration but human activities continue on schedule, it could spell trouble. For example, commercial fishing in the Northeast typically ramps up in the fall. Sharks that remain in the area face a higher risk of accidental catch.

“Our findings suggest that climate change could increase vulnerability to bycatch, particularly in mixed-use areas like the New York Bight,” the authors wrote.

There is also concern that shark diets and reproductive cycles may shift out of sync with prey availability. A mismatch in timing could reduce feeding success or breeding success.

New strategies for a changing ocean

Static conservation policies will not hold up if shark behavior keeps changing. The researchers suggest dynamic management tools, like adjusting fishery closures based on temperature data.

Sandbar sharks, which showed the most migration delay, may require special focus. They are already listed as vulnerable due to previous overfishing and slow reproduction.

Successful conservation now depends on real-time data and predictive modeling. As this study shows, changes in migration are not hypothetical. They are already underway.

Shark migration is shifting with warming

The timing of shark migrations is shifting. Some species are adapting by staying longer in warming northern waters. While that may suit them for now, it raises questions about long-term ecological impacts.

Maria Manz and her team stress the importance of using both regional climate data and shark movement models. Doing so can improve predictions and help managers adjust strategies before the ocean changes even more.

“Our study adds to the growing body of evidence demonstrating how migratory populations will respond to a warming climate, potentially altering regional ecosystem dynamics and exposure to anthropogenic threats.”

The research is published in the journal Conservation Biology.

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