Wednesday, October 11, 2017

Survey Shows Substantial Drop in Gulf of Alaska Cod Stocks

Results of 2017 surveys and preliminary modeling for the 2018 Pacific cod stock assessment show a 71 percent reduction in the Gulf of Alaska bottom trawl survey Pacific cod biomass estimate from 2015 to 2017. The news came to the North Pacific Fishery Management Council’s Scientific and Statistical Committee and Advisory Panel on October 3 in a presentation from Steve Barbeaux, a research biologist with the Alaska Fisheries Science Center in Seattle, Washington, who said the drop was particularly pronounced in the central Gulf of Alaska.

The Science and Statistical Committee (SSC) said Barbeaux also presented additional data that appeared to corroborate the trawl survey results, including a 53 percent drop in the National Marine Fisheries Service 2017 longline survey and low estimates in recent years by the Alaska Department of Fish and Game large mesh trawl survey. Pacific cod fishery data from 2017 indicated slower rates of catch accumulation and lower catch per unit effort over the season, at least in the central Gulf, compared to recent years, as well as a change in depth distribution toward deeper waters.

The survey results, Barbeaux said later in an interview, were not what he expected. “Recruitment in 2011-2012 was strong,” he explained. “We expected that would carry us to 2019. We expected a drop in 2019 because we had low recruitment in 2013-2015.” There are still three levels of review to go, by the stock assessment team, the Groundfish Plan Team, and the SSC before the numbers are finalized.

Evidence indicates that the “blob” is a likely culprit. The blob is the name scientists have given to a large mass of warm water in the Pacific Ocean, which adversely affects marine life.

Temperature records indicate very warm temperatures across a broad range of ocean depths from 2014 through 2016 associated with low forage fish amounts in Pacific cod diets. That likely resulted from low prey availability in 2015 and 2016, which was evident in seabird mortalities due to starvation, as well as other ecosystem indicators. In very warm temperatures the cod would have had to eat quite a bit more to grow and survive, but there was less in the water column for them to eat.

“That was the black swan effect,” said Barbeaux. “It has never happened before as far as we know. We have had warm years before, but this blob went on for three years, and throughout the entire water column across the Gulf of Alaska shelf, even in winter.”

The cod would have needed to keep eating a lot more for three years straight, but in fact “they were in the worst condition we’ve seen, the lowest weight for a given length,” he said. “In the central Gulf, it was the same in the longline and pot survey.”

On a brighter note, cod “are a highly reproductive species, so if conditions are right they can bounce back fairly rapidly,” Barbeaux said. Still it would take at least three years for them to become large enough to harvest.

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