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Cod Tagging Project Suggests Fish Don’t Overwinter in Northern Bering Sea

A net full of cod fish caught in the Bering Sea near Nome. Photo from Davis Hovey, KNOM (2020).

As the number of Pacific cod swimming into the Northern Bering Sea continues to increase, scientists have gathered initial data on the fish’s movements. Even though they have a small sample size, National Oceanic and Atmospheric Administration (NOAA) researchers believe that cod are unable to survive under the ice in the Bering Sea.

Susanne McDermott, a fish biologist with NOAA Fisheries, says that after tagging 38 fish last year, none of them stayed in the Northern Bering Sea over the winter.

“So we actually had one tag recovered under ice. This fish most likely died in January under the ice, but the tag popped up close to the Bering Strait. We don’t think the fish actually went all the way there, we think the tag was moved there by the ice most likely, or [ocean] currents.”

– Susanne McDermott

Some of these tags were staggered to pop up after 90 days, 210 days, or even 360 days later. So far, McDermott says, they’ve recovered 30 of the 38 tags originally sent out last fall.

“And then two of the tags have not been heard from. We assume maybe those fish got trapped under the ice and those tags tried to transmit, and never got to transmit or something. But so far, really high success rate. We have very little mortality, and most of the tags have worked.”

– Susanne McDermott

McDermott and her fellow researchers are tagging cod to answer some key questions about these fish: Can they spawn successfully in the Northern Bering Sea? Do they return to that part of the Bering Sea? And if not, where do they go?

These are all important questions to answer as the disappearance of the cold pool in the Northern Bering Sea has resulted in a more than 30% increase of Pacific cod within the region since 2017.

“So you can see in 2010 you have this large cold pool. In 2017 it was still large but breaking up a little bit, but then look at 2018, there’s almost no cold pool, and in 2019 it was only in that northern part. So why is that important, it’s important because a lot of fish don’t like to be inside this cold pool, and they avoid it. So once this cold pool is gone, there’s a little bit more area for these fish to go.”

– Susanne McDermott
NOAA Fisheries Biologist Susanne McDermott tags a Pacific Cod with the assistance of another NOAA Fisheries biologist and NSEDC staff. Photo from Dawn Wehde, NSEDC (2019).

A large portion of these fish were found around St. Lawrence Island, which is why McDermott and Norton Sound Economic Development Corporation biologists collaborated with Savoonga fishermen like Perry Pungowiyi to tag the cod.

According to Pungowiyi, the initial findings from this tagging project have not yet been relayed to him, so he did not want to comment on the research at this time. However, Pungowiyi did say that local cod and halibut fishers, like himself, are actively fishing again this season, when the weather is good enough to go out.

From September to December of 2019, nine fish stayed in the Northern Bering Sea near the island. After that time though, McDermott says the cod spread out into the Southern Bering Sea and some went across the International Date Line.

“Six out of 30 tags were recovered in Russian waters. Three in September to December, three from January through March, but none of them in June or July. So yes, there is definitely movement between Russian and U.S. border. I think we need a little more data to see how consistent that is and if fish maybe move back or not, into Alaskan waters after they were in Russia.”

– Susanne McDermott

Although none of the cod spawned in the Northern Bering Sea, four more tags, expected to pop up later this month, could indicate that a fraction of the tagged fish returned this year to the area near St. Lawrence Island.

According to McDermott, NSEDC staff like Dawn Wehde and Myra Scholze along with the local ADF&G office are helping to tag more cod this summer.

Image at top: A net full of cod fish caught in the Bering Sea near Nome. Photo from Davis Hovey, KNOM (2020).

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