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Thu May 16, 2019, 07:33 AM

Record Bering Sea Ice Loss Already Powering Rapid Changes In Fisheries, Ecosystems


he ice retreat could also reflect an unexpected warming of the Bering Sea, says Seth Danielson, an oceanographer at the University of Alaska in Fairbanks who tracks Bering Sea temperatures. In early 2018, temperatures in the northern Bering Sea were as much as 2°C higher than normal, and Danielson expects the data to show the warm trend continued this past winter. He suspects a troubling feedback: Low ice coverage in 2017 would have allowed open water to absorb more heat, paving the way for even more ice loss in later years. He estimates that every additional degree delays the start of ice formation by 3 weeks. "It doesn't take too many degrees of warming to severely cut down the number of days of ice," he says.

Regardless of whether they prove lasting, the ice changes are already rippling through the ecosystem. Sea ice is home to the algae that underpin much of the food web in the northern Bering. The algae bloom in 2018 was small, as was the number of zooplankton feeding on it, according to NOAA. The small forage fish that feed on the zooplankton in the sea's northern reaches were scarce as well, and people in the region reported an unusual die-off of common murres, a seabird that feeds on these fish.

A massive "cold pool" of water in the central and northern Bering normally confines commercially valuable fish such as walleyed pollock and Pacific cod to the southern part of the sea. In 2018, the pool was the smallest ever seen, presumably because of the lack of winter ice. Research ships caught fewer fish than normal in the usual fishing grounds. With the cold pool virtually gone, it appears many of the fish had sped north.

If such changes persist, they could scramble one the most lucrative U.S. fisheries. Boats in the southeastern Bering Sea haul up a cornucopia of seafood: king crab, halibut, turbot, and cod. The pollock fishery—the region's largest—alone produced $1.3 billion worth of fish in 2017. If the fishery shifts north, existing fish-processing factories could be stranded too far from the fishing grounds to be economical, Foy notes.



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