Fewer Pollock, cod found in southern Bering Sea survey

Lack of ‘cold pool’ acting as a barrier may have caused fish to stray north

Formal results of this year’s NOAA trawl survey of the southern Bering Sea won’t be announced until mid-September, but preliminary data shows a decided warming trend and the presence of fewer Alaska Pollock and Pacific cod than anticipated.

“It appears that conditions are such now that we are moving into a warming phase and there is not clear evidence that we will move back into a cold phase,” said Lyle Britt, a research fisheries biologist with NOAA’s Alaska Fisheries Science Center in Seattle who participated in this year’s survey.

What they found in the recently completed survey was Pollock and cod swimming all the way up to the Bering Strait and not concentrated in the areas where they are normally observed.

“The whole area is starting to look different,” said Britt, in an interview about preliminary survey observations. While survey results are still being compiled, it is obvious that the ecosystem, compared to what it has been over the past 37 years of the survey, is in flux.

The only hard data researchers have so far is temperature data, which shows that south of St. Lawrence Island the usually present “cold pool” formed by sea ice settling to the ocean floor was absent. It is that cold pool the acts as a natural barrier to fish migration, inhibiting Pollock and cod from heading north of the Bering Strait.

Pollock and cod don’t want to venture into the cold pool because below 2 degrees Celsius their metabolic rates go down, so they can’t process food as well, they can become lethargic and they are not as reproductively fit for the long term, Britt said. Without that cold-water barrier in place, these fish could very well have strayed outside of the southern Bering Sea. The surveys involve two vessels working about 65 days each, sailing into the center of a number of 20 nautical mile squares to do a bottom trawl.

“We collect data on everything and all that data goes into models that help us assess the health of the habitat,” said Britt.

While the annual surveys are focused on the entire ecosystem, rather than Pollock, cod or king crab, researchers on this year’s survey noted the lack of the cold pool as well as the lower numbers of Pollock and cod.

Back in 2010, and again in 2017, NOAA did conduct a trawl survey of the northern Bering Sea shelf. This year they came back to do a modified sampling in grids of 30 nautical mile squares, but until that data is worked up, there’s not much we can conclude, he said.

Final data compiled from all these surveys will be used by the North Pacific Fishery Management Council in determining allowable commercial harvests of various species in the coming year.

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Margaret Bauman is a veteran Alaska journalist focused on covering fisheries and environmental issues. Bauman has been writing for The Cordova Times since 2010. You can reach her at mbauman@thecordovatimes.com.