Sharks staying in Long Island waters longer as sea temperatures rise, Stony Brook study shows

As sea surface temperature rises, some shark species could linger in northern waters nearly a month longer than usual, disturbing the ecosystem and interrupting conservation efforts, a Stony Brook University study found.

Over five years, a team of Stony Brook scientists tagged 155 sharks along the East Coast and tracked their movements using underwater sound signals. The six highly migratory shark species studied annually migrate from the Northeast and Canada to waters ranging from the Carolinas to Florida during the early fall.

Lead author Maria Manz, a doctoral student, used the data to develop mathematical models that helped predict how each shark species travel and what environmental factors play the biggest role.

"It's really important that we monitor and research both the negative and positive responses specific species have to climate change because it will impact how we manage them moving forward," Manz said. 

Delays in sharks migration south could disrupt predator-prey relationships and interfere with ongoing conservation efforts, the study found. 

The team found sandbar sharks had the greatest predicted delay at about 29 days later than usual, while sand tiger and white sharks had a predicted delay of only one day. Temperature and sunlight were identified as the biggest influences, signaling to sharks it’s time to head south for the winter.

The length of sunlight, also known as photoperiod, is a strong stimulant for reproductive behaviors, including migration to reproductive areas, and serves as an external indicator of time. Sea temperature is linked to biological processes, feeding and digestion and reproductive efficiency.

As apex predators, sharks impact the population and behavior of their prey and potentially other species in the ecosystem, according to Manz. For example, species that remain in the New York Bight during the winter, a region in the Atlantic Ocean, would experience increased predation pressure if sharks stayed longer.

Craig O’Connell, co-founder of a Montauk nonprofit called the O'Seas Conservation Foundation, said this could have drastic implications.

"Whenever you change something in the environment, there’s always some sort of repercussion ... We can’t exactly say what’s gonna happen, but most of the time it’s not good," O’Connell said.

Manz said it’s important to continue monitoring how species respond to changes in their ecosystems because it could impact conservation efforts. She said all of the species they focused on are either vulnerable, threatened, endangered or critically endangered, as per the International Union for Conservation of Nature.

"State by state, a lot of these species, such as the sandbar, sand tiger and dusky sharks for New York, are prohibited species. There's a lot of management actions that are tailored toward the recovery of these species ... if migration timing is off, fishing regulations, for example, may become misaligned and an area may be closed off prematurely or too late," she said.

Jon Dodd, executive director of the Atlantic Shark Institute, said: "Shark health is ocean health ... We want people to understand the importance of sharks in this ecosystem and that an ocean without sharks is not healthy."

Manz said collaborating with OCEARCH, Monmouth University, the New York State Department of Environmental Conservation, the Atlantic Shark Institute, New England Aquarium and the National Oceanic and Atmospheric Administration was key to completing this study.

Dodd said no organization has the money or bandwidth to independently complete this type of study within the five-year time frame. As climate change rapidly intensifies, Earth is no longer in a position where researchers can take their time, he added.

"Collaborating is much more effective for ocean health ... Rather than take five times longer to get an answer on something that could be critical to policy decision making, let's work together to get these answers more quickly," Dodd said.