Mar 12 2015

OSU and NOAA Researchers Expect Low Oxygen Waters to Expand off West Coast Affecting Fisheries

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SEAFOODNEWS.COM [SeafoodNews] – March 12, 2015

When low-oxygen “dead zones” began appearing off the Oregon Coast in the early 2000’s, photos of the ocean floor revealed bottom-dwelling crabs that could not escape the suffocating conditions and died by the thousands.

But the question everyone asked was, “What about the fish?” recalls Oregon State University oceanographer Jack Barth. “We didn’t really know the impacts on fish. We couldn’t see them.”

Scientists from NOAA Fisheries’ Northwest Fisheries Science Center and Oregon State have begun to answer that question with a new paper published in the journal Fisheries Oceanography. The paper finds that low-oxygen waters projected to expand with climate change create winners and losers among fish, with some adapted to handle low-oxygen conditions that drive other species away.

Generally the number of fish species declines with oxygen levels as sensitive species leave the area, said Aimee Keller, a fisheries biologist at the Northwest Fisheries Science Center and lead author of the new paper. But a few species such as Dover sole and greenstriped rockfish appear largely unaffected.

“One of our main questions was, ‘Are there fewer species present in an area when the oxygen drops?’ and yes, we definitely see that,” Keller said. “As it goes lower and lower you see more and more correlation between species and oxygen levels.”

Deep waters off the West Coast have long been known to be naturally low in oxygen. But the new findings show that the spread of lower oxygen conditions, which have been documented closer to shore and off Washington and California, could redistribute fish in ways that affect fishing fleets as well as the marine food chain.

The lower the oxygen levels, for example, the more effort fishing boats will have to invest to find enough fish.

“We may see fish sensitive to oxygen levels may be pushed into habitat that’s less desirable and they may grow more slowly in those areas,” Keller said.

Researchers examined the effect of low-oxygen waters with the help of West Coast trawl surveys conducted every year by the Northwest Fisheries Science Center to assess the status of groundfish stocks. They developed a sturdy, protective housing for oxygen sensors that could be attached to the trawl nets to determine what species the nets swept up in areas of different oxygen concentrations.


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