Some Tiger Sharks Are Migrating Farther North Due to Climate Change – Smithsonian

January 14, 2022 by No Comments

A tiger shark swims in the Bahamas. Over the past several decades, the predators ventured farther north in the northwestern Atlantic Ocean.
Neil Hammerschlag

The waters off the northeastern coast of the United States are some of the fastest warming in the world. Human-caused climate change has warmed this part of the Atlantic about 2.7 degrees Fahrenheit since the 1980s.

These rapid, profound alterations have rewired marine ecosystems, causing some species to move into new areas and others to disappear from places they once called home. The cold water habitats favored by Atlantic cod, for example, are predicted to nearly disappear off the coast of New England over the next 60 to 80 years—a shift that will severely complicate attempts to revive the fishery after it collapsed in 1992.

New research published today in Global Change Biology shows that this extreme warming is also changing the migrations of one of the region’s apex predators: the tiger shark. These sharks, which can exceed 15 feet in length and dine on anything from sea turtles to lobsters to car parts, are venturing roughly 270 miles farther north in the summertime and arriving about a month earlier than they did in the 1980s. The sharks’ changing migratory patterns almost perfectly track the shifting water temperatures the species most prefers.

The study, which combines nearly ten years of satellite tracking data with 40 years of catch records, shows that this large and toothy species is making swift and significant changes to its range to cope with and take advantage of climate change.

“Apex predators help control and regulate their home ecosystems,” says Neil Hammerschlag, a shark researcher at the University of Miami and lead author of the study. “But we don’t know exactly how tiger sharks will impact the ecosystems they’re moving into.”

The findings also have implications for the species’ conservation because as these tigers of the sea move farther north, they’re spending more and more time outside of waters with some form of protection from commercial fishing.

“The wild tiger shark population is relatively stable,” says Hammerschlag. “But if these sharks start getting killed by the commercial fishing industry in greater numbers that could change. Tiger sharks reproduce and grow slowly, which makes them more vulnerable to threats like fishing.”

In the northwestern Atlantic, the tiger shark’s typical seasonal patterns are not unlike those of certain wealthy retirees: they spend the winter months in the tropics near Florida or the Bahamas and only venture farther north once things warm up in the summer. These summertime jaunts to points north in search of food usually don’t extend past Virginia, but can take the sharks as far as Massachusetts.

As climate change has cranked up the heat in the ocean, the balmy water temperatures—between 70 and 80 degrees—that tiger sharks prefer are arriving earlier in the year and extending farther north than they did 40 years ago. That shift led Hammerschlag and his collaborators to ask the question: how were tiger sharks responding to these changing conditions?

To figure out the answer, the team captured 47 tiger sharks off southeast Florida, southwest Florida and the northern Bahamas and outfitted them with satellite tracking devices to monitor the sharks’ movements from 2010 to 2019.

To add historical context, the team combined these new, detailed tracking data with the times and locations of 8,764 tiger sharks that were caught and tagged by scientists and fishers between 1980 and 2018 as …….



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