Lack of ‘Cold Pool’ Observed in Southern Bering Sea Trawl Survey

For the past 37 years, annual trawl surveys of the southern Bering Sea have identified a “cold pool” south of St. Lawrence Island, a natural barrier that kept Alaska Pollock and Pacific cod from swimming beyond that area. This year there was none.

“We did find Pollock and cod all the way up to the Bering Strait, but they were not concentrated in the normal areas,” says Lyle Britt, a veteran research fisheries biologist with NOAA’s Alaska Fisheries Science Center who was involved in the survey.
“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, but that doesn’t mean you can’t have a cold pool… because of the influx of climate change and weather,” he said.

The annual surveys, used in part by the North Pacific Fishery Management Council to determine commercial groundfish allocations, collect data on everything, and that data, said Britt, goes into models that help assess the health of the habitat.
Researchers trawl the bottom of each of dozens of measured squares in what has been considered a closed ecosystem and as they march across they expect fish to move around but that cold pool is critical to movement of the fish.

“Pollock and cod don’t want to go 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 (long term) as reproductively fit,” Britt added. “We started realizing we were not seeing cold pool waters and there was not much ice last year. We also started to see that catches of Pollock and cod were lower than what we would historically see.”

Britt said the whole ecosystem is starting to look different, not just the commercial fishery, but cautioned that at this time the only hard data they have is the temperature data. “It is alarming to not have a cold pool for the first time in 37 years of the survey,” he said. “This can have some effect on distribution of the fishes, but until we have all the results from the survey processed, I don’t have any hard numbers to give you.”

Meanwhile there are no firm answers on whether the biomass of these groundfish has declined or these fish have moved outside the survey area.