As the weather turns cold, the sharks are drawn away from their northern feeding grounds, in places like Cape Cod and Nova Scotia, towards warmer water in Florida, Georgia and the Carolinas.
OCEARCH, a marine conservation group, has been tracking the movements and migrations of these sharks in the North Atlantic for over a decade. It hopes that its data will help inform future conservation strategies to protect these animals in the face of a changing climate.
The team has found that these shark populations perform annual north-south migrations within their range, which extends from Newfoundland to the eastern Gulf of Mexico.
In a Facebook post, OCEARCH announced its first southbound shark of the year.
Andromache, a 340-pound great white, has begun her annual migration early two years in a row.
An unusually long La Nina climate pattern has been in place across the Pacific for the last three years, which tends to bring colder-than-average temperatures to New England and the West Coast. This could have impacted the sharks’ annual movements.
“Sharks move with water temperature,” Stephan Kajiura, a professor who studies shark migration at Florida Atlantic University, told Newsweek. “In warm years they stay north longer, and in cold years they come down here sooner.
“For white sharks tagged in Massachusetts in the summer, we can detect them down here in southeast Florida in the winter. So we know that these white sharks are migrating along the entire U.S. Eastern Seaboard.”
As the climate changes, so too do the sharks’ movements. “Water temperature is a primary motivator of migration in marine organisms, so changing climate can affect movement of animals,” said Kajiura.
He and his team have been closely studying the movements of another shark species, the blacktip, with an overlapping range with the great whites.
“We have seen our blacktip sharks migrate farther north in greater numbers now than before,” Kajiura said. “These sharks seem to prefer a certain temperature range and they will migrate within that temperature. Now that water temperature is rising, the sharks are going farther north in greater numbers to remain within their preferred temperature.”
As apex predators, sharks play an important role in the ocean’s ecosystem, keeping prey populations in check and maintaining the overall diversity of ocean communities. Changes in shark migratory patterns could affect wildlife in the areas that they normally visit, reducing species diversity in their old feeding grounds while threatening prey populations in their new habitat.
With the warming of our oceans, human encounters with species like the great white shark could become more common.
“As global climate change causes the water temperature to rise, there will be not only more people in the water, but probably more sharks in the same place as those people,” said Kajiura. “This will result in increased interactions between the two.”
