Report: Climate change has affected cod fisheries
Posted by the Asbury Park Press on 06/18/07
BY KIRK MOORE
STAFF WRITER

http://www.app.com/apps/pbcs.dll/article?AID=/20070618/NEWS/706180326/1001/DWEK01


Climate change already affects ocean ecosystems and seafood production off the shores of North America, according to a new report on the long decline and now-stalled recovery of Atlantic cod and a decision by Alaska fisheries regulators to seal off America's farthest northern waters to fishing.

Warming in the Arctic may be one reason why cod are so slow to return to Atlantic waters, despite years of increased restrictions on fishing, says Brian Rothschild of the University of Massachusetts.

"Everyone has attributed the declines of cod, especially in Canada, to overfishing," said Rothschild, dean of the UMass School for Marine Science and Technology. In a newly published analysis of cod stock assessments and other data used by American and Canadian government agencies to set catch limits, Rothschild says he detected a widespread pattern of fish abundance and decline since 1985 more in tune with ecological changes in the northwest Atlantic.

"Fishermen often say these up and down changes (in fish abundance) run in cycles, and to some extent they're right about that," said Rothschild, who works at the Dartmouth campus in New Bedford, a home to the New England cod fleet.

Now, "fishermen think things are changing in the Atlantic," he added. "If this is part of a global climate change event, these things may not come back."

Scientists at Rutgers University are tracking changes in Mid-Atlantic waters that they think are related to temperature, from the appearance of stinging sea nettle jellyfish in Barnegat Bay to the slow shift northward of surf clams, New Jersey's single biggest seafood crop and the primary source of America's clam chowder.

Last week, the North Pacific Fishery Management Council made history when it summarily prohibited any bottom-trawl commercial fishing off the far north of Alaska past the Bering Strait - at least until scientists figure out the effects of sea ice retreat and warming.

"It's probably the first time in the history of the world a fishery management agency has said "We're not going to allow any commercial fishing here,' " said Dave Benton of the Marine Conservation Alliance, a Northwest coalition of fishing and conservation groups that advocates applying the firm fishing limits of Alaska to other regions.

In recent days, the North Pacific council closed 130,000 square miles north of the Bering Strait to bottom trawling. That decision won't affect any American fishermen, but Benton said other fleets are already probing newly ice-free waters off Russia and eastern Canada.

It will probably be five to six years before the effect of ice retreat is clear off Alaska, Benton said, but some fishermen already report sea animals on the move.

"This is very preliminary, but we're seeing some shift northward. Sole in the Bering Strait seem to be on the move. Some fishermen say they're seeing them move 20 to 50 miles a year now. Those changes can be very rapid in this part of the world," he said.

From New England south to New Jersey, fishermen are still waiting for the cod to return. Heavily overfished for years, the species was already handicapped by changes in the northwest Atlantic's ecosystem, some brought on by warming temperatures, says UMass dean Rothschild.

"The so-called "great salinity anomaly' is a pool of fresh water that comes out of the Labrador Sea - and migrates across the Atlantic," Rothschild said. That surge has been enhanced over the years by melting ice and runoff from Canada's high Arctic islands, he said.

Out on the ocean, the pooling of lighter, fresher water over saltier water retards mixing of those layers and the biological productivity that usually results, according to Rothschild and earlier researchers. So there's been less growth of microscopic plants and animals, and less food for small fish, hence less food for cod, they say.

"The stocks of forage fish changed, the cod got skinnier," Rothschild said.

Rothschild's paper shows cod were going into decline even before heavy fishing pressure hastened the trend, fisheries professor Ray Hilburn of the University of Washington said in comments published by UMass.

That notion will be controversial. When the New England Fishery Management Council meets Tuesday in Portland, Maine, the environmental group Oceana will call for designating some ocean areas as special cod habitat. The stocks have dwindled "because commercial fishing caught too many while at the same time destroying their habitat by plowing over the gravel and cobble habitats that cod use for shelter," the group said in a statement Thursday.

"Separating environmental forcing from fishing mortality continues to be a major challenge," Rothschild acknowledges in his paper, published this month in the Transactions of the American Fisheries Society journal. Still, "the remarkable lack of recovery of the cod stocks under a fishing moratorium" in Canada along with changes to the cod stocks and ecosystem suggest "that the effects of fishing that exist may not be as important as previously thought," he wrote.

New Jersey fishermen could catch cod in the 1950s and '60s until foreign fishing boats cleaned out most of the southern stock; recreational anglers still catch some on offshore wrecks. To the north, cod stocks remain depressed after years of catch limits. There's modest signs of recovery in some areas, but almost none in the eastern Gulf of Maine.

To bring cod back, "the forage structure (of microorganisms and small fish) would have to be reconstituted," Rothschild said. "If this is part of global change," he added, "this might not be reversible."

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