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Predatory fish could lose 40 percent of habitat by 2100, with Northwest Atlantic a hot spot, study finds

A mako shark in the Atlantic Ocean offshore from Cape Cod.Tom Burns

It’s been a record year for ocean warming, with a months-long marine heat wave in the Gulf of Mexico and another heat wave that just arrived off the West Coast.

But ocean warming is not without consequences, especially for the marine life beneath the surface.

A new study has found that highly migratory fish predators in the rapidly warming Northwest Atlantic Ocean and Gulf of Mexico could lose around 40 percent of their suitable habitat — nearly 70 percent for some — by the end of the century.

Findings from the study, conducted by the Woods Hole Oceanographic Institution in Massachusetts and published in the journal Science Advances on Wednesday, could have a far-reaching impact for New England fisheries and consumers, experts say.

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The study analyzed highly migratory species that include the kind of fish you might eat at a sushi restaurant, like tuna and billfish, as well as sharks: Researchers looked at five tuna, four billfish, and three shark species.

A blue shark in the Atlantic Ocean off of Cape Cod.Tom Burns

“It’s pretty concerning that across the board, these species are expected to have significant declines,” said lead researcher Camrin Braun, an assistant scientist and marine ecologist at WHOI.

The study used NASA modeling technology to map the relationship between the climate and the ocean in recent decades. Researchers then used those insights to extrapolate how climate change-driven increases in surface ocean temperatures by 1 to 6 degrees Celsius would affect marine species.

Though one species, the Atlantic blue marlin, may gain 5 percent to 8 percent suitable habitat, most species could lose around 40 percent of their habitat, with Atlantic bluefin tuna and shortfin mako shark potentially losing upward of 60 percent, according to the study.

It’s unclear whether these fish will migrate to and overcrowd other areas of the ocean, or if they’ll face higher mortality rates as their current habitats warm up. But Braun said that bluefin tuna, commonly fished off the Massachusetts coast, have already started migrating northward, and shortfin mako sharks are expected to follow suit by the end of the century.

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“There’s going to be a series of unknown, cascading effects when we have large predators moving to account for climate change,” said George Lauder, who studies fish behavior as a professor of organismic and evolutionary biology at Harvard University.

Lauder, who was not involved with the WHOI research, said he “completely agrees” with the study’s analysis.

Changes in predatory fish populations could cause “significant disruption to New England fisheries,” he said, changing which fish and how many of them are available. While species used to colder water may migrate northward, new species looking for warmer waters could move into these regions, and those fish could be more or less valuable, affecting how much money fisheries could make from their sales.

“We expect continued distribution changes with warming, and that’s going to have consequences for commercial and recreational fisheries,” said Vincent Saba, research fishery biologist at the National Oceanic and Atmospheric Administration, who was not involved with the study.

Habitat loss can also have a series of domino effects on marine ecosystems because predatory species regulate lower species in the food chain. A lack of predators can lead to overpopulation of prey species, but more predators than usual can mean there won’t be enough food for them in their new habitat to survive.

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The Northwest Atlantic and the Gulf of Mexico are among the earth’s fastest-warming ocean regions, and climate change has already warmed the oceans significantly, said Michael Rawlins, associate director of the Climate System Research Center at the University of Massachusetts Amherst. Because water has a high heat capacity, the ocean absorbs 90 percent of the excess heat caused by anthropogenic climate change, he said.

But the heat is not absorbed uniformly by the oceans; climate change has shifted the drift of an oceanic current called the Gulf Stream, which is causing some regions like the Northwest Atlantic and the Gulf of Maine to warm faster than other regions, Saba said.

Experts agree that the biggest variable that remains after this study is marine life adaptability; the study could not account for how predators may adapt to thermal changes, though Braun is optimistic that highly mobile species may be able to adapt to warming or cooling in ocean temperatures. But how they do so remains unclear, and any changes to fish migration patterns have the potential to disrupt the fishing industry.

Traditionally, fish zones are designated by essentially “drawing a box in the water” to say whether fishing there is legal or not, according to Braun. But these fixed zones could be rendered obsolete if fish populations are moving, and fisheries will need to decide whether that box will shift to follow migratory fish or if management practices must be overhauled altogether.

Even fishing gear could be affected; as fish species change, the gear and equipment to catch such fish may need to change as well. And the cascading effects could reach customers near and far.

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“We expect climate change winners and losers,” Saba said. “The question is: Can management [regulations] keep up?”

Outlining all the impacts of such habitat loss at this point in time is impossible; “We’re entering a global experiment,” Lauder said.

“This feels doom and gloom, but it’s an opportunity,” Braun said. With the latest modeling techniques, he hopes that scientists and conservation managers will take these findings as an opportunity to better understand how to sustainably harvest in order to protect the animals as well as ensure coastal fisheries are climate resilient.


Sarah Raza can be reached at sarah.raza@globe.com. Follow her @sarahmraza.