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Blue crabs in Maine? Something fishy about global warming.

Warming oceans are changing the mix of species in the world's fisheries, according to a new study. Marine-ecosystem models have indicated that this could be an effect from global warming.

By Staff writer / May 16, 2013

Lobsterman Mike Horning paddles his skiff across Perkins Cove after returning from fishing on a mild winter day, in Ogunquit, Maine, in February. Warming oceans are changing the mix of species in the world's fisheries as fish try to remain in waters in their preferred temperature range, according to a new study.

Robert F. Bukaty/AP

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Warming oceans are changing the mix of species in the world's fisheries as fish try to remain in waters in their preferred temperature range, according to a new study.

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The movement to keep pace with preferred temperatures shows up most starkly in the northeastern Pacific Ocean and the northeastern Atlantic Ocean, as fish migrate out of the subtropics to beat the heat.

The changes have particular implication for people living in the coastal tropics who either subsist on fishing or fish commercially, the research team says. If ocean temperatures continue to warm there, the heat could top a level that even tropical species find intolerable, reducing their abundance, the researchers say.

This raises the urgency of adopting approaches that minimize other stresses on fisheries, such as pollution and overfishing, the team says.

Marine-ecosystem models have indicated that global warming's impact on ocean temperatures would trigger such a migration. And studies of individual regions have documented the arrival of species from warmer aquatic climes.

This latest effort represents the first attempt at documenting the changes for the planet as a whole, says William Cheung, a scientist with the Fisheries Centre at the University of British Columbia in Vancouver, who led the team. The techniques that the team used, along with the results, appear in Thursday's issue of the journal Nature.

The general pattern reported in the study is "very similar" to results from studies that have focused on the US Northeast's fisheries, says Michael Fogarty, who heads the ecosystem assessment program at the National Oceanic and Atmospheric Administration's Northeast Fisheries Science Center in Woods Hole., Mass.

Off the New England coast, for instance, marine scientists tracked migration trends for 36 fish species and found that 75 percent had moved north or into deeper water or both to keep their cool, Dr. Fogarty says.

At the same time, "the Atlantic croaker, a subtropical species, is moving north and is having higher reproductive success as well" in northern waters, he says.

Meanwhile, fishermen in the Gulf of Maine are reporting highly unusual species for the area: black sea bass, which could earn them a tidy sum; new species of squid; and blue crabs, Fogarty adds.

The work by Dr. Cheung and colleagues "is a very interesting study, and its global reach makes it quite important," he says.

The study covers a period spanning 1970 to 2006. The team examined catch records compiled by the United Nations Food and Agriculture Organization, as well as from regional and national fisheries groups. The researchers divvied the catch data among 52 large marine ecosystems – for example, the US Northeast's continental shelf, the North Sea, or ecosystems defined by currents such as the Canary Current (a segment of a much larger North Atlantic surface current that skirts the Canary Islands).

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