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Trawl Survey Results Show Northern Bering Sea In Flux

Blue and white boat on the water
The Vesteraalen, one of two boats used by NOAA Fisheries to do the bottom trawl survey in the Bering Sea. Photo: Lyle Britt, used with permission.

Norton Sound Red King Crab are moving, Arctic cod numbers have dropped significantly, and Pacific cod are continuing to increase as the Northern Bering Sea ecosystem undergoes drastic change. That’s all according to preliminary results from NOAA Fisheries’ trawl survey this summer in the Northern Bering Sea (NBS).

KNOM’s Davis Hovey has more:

Before Lyle Britt even began leading the NOAA Fisheries’ study of the NBS in September, he anticipated seeing more warm water fish in a region that stretches from Nunivak Island north to the Bering Strait.

“We can tell that the ecosystem is very much in flux up here. We’re seeing expansion of ranges of some fish and invertebrates, and we’re seeing the retraction of others. Now how permanent or ephemeral those are, I think is still in question.”

– Lyle Britt

As an example of a species that’s expanding its range based on what was discovered in the 2010 baseline survey of the Northern Bering Sea, Britt points to Pacific cod.

“Between 2010 and 2017 there was about a 900% increase in the amount of Pacific cod we saw in the Northern Bering Sea region, based on that biomass or total weight estimate. That number sounds really dramatic in part because there were so few in 2010 and now there are some. That number increased between 2017 and 2019 by about 30%, so it’s continued to go up.”

– Lyle Britt

From 2010 to 2019, according to Britt, walleye pollock increased by 5,400% starting at 21,000 fish in the baseline year of 2010 to now having over a million fish in the Northern Bering Sea.

Duane Stevenson, a research fishery biologist with NOAA’s Alaska Fisheries Science Center, says besides the Pacific cod and walleye pollock, northern rock sole are also showing up in larger quantities in the NBS.

“Back in 2017 we saw some really young northern rock sole in the southern part of what we call the Northern Bering Sea area, so down near Nunivak Island but further north than we would expect to see them. And this year we’ve continued to see those fish, only they’re larger now. So we are certainly seeing some recruitment happening with northern rock sole in what we call the Northern area, and those fish are persisting and growing.”

– Duane Stevenson

As some fish move in, Britt says there are others that are moving out of the Northern Bering Sea in numbers that are striking, such as Arctic cod.

“When you go from what we saw in 2010 to 2017, there’s about a 90% drop in Arctic cod in the region in our survey data. When you go from 2017 to 2019 we dropped 99%, and in fact we’re at numbers now where you could count how many Arctic cod we catch on your fingers.”

– Lyle Britt

For all of these species and others in the Northern Bering Sea, Stevenson says tracking their movements to know where they are coming from and if all of them are moving north, or if some, like the rainbow smelt, could be moving further south, is still too difficult to determine at this time. 

According to Britt, using genetic collections as well as more tagging projects, like the one NOAA conducted with Savoonga fishermen for Pacific cod earlier this summer, will help scientists better understand movement of fish in the Northern Bering Sea.

NOAA Fisheries’ Lyle Britt gave a couple Strait Science presentations in Nome this year. Photo from Emily Hofstaedter, KNOM (2019).

When Britt visited Nome in August for a Strait Science presentation ahead of the trawl survey, several residents and crabbers expressed interest in knowing what happened to the Norton Sound Red King Crab. NOAA Fisheries now has a possible explanation for why commercial crabbing in the Norton Sound was so poor this summer.

“One thing is that actually our total biomass, that total weight estimate, is up, it’s higher. However that is tempered by the fact that it’s actually greatly down for legal size, what you would consider to be the commercial size for harvest of crab. So there’s a lot of young crab in the system, but not a lot of legal size Red King Crab. Also based on our survey data Red King Crab are slightly deeper. So they appear to be moving into deeper water than what we’ve seen in the past.”

– Lyle Britt

There are many possible reasons why Red King Crab would choose to go into deeper waters, but Britt says a likely cause is the warmer water. He cited record bottom-level temperatures in Norton Sound this year at 14° Celsius and surface temperatures up to 20° Celsius.

In fact, Britt mentioned that the research team had to change their models for analyzing bottom-temperature data because what they were seeing this summer was outside of their model parameters.

Similarly, warm water has been linked to the drastic changes and movements of fish in the overall Northern Bering Sea ecosystem, as Britt explains.

“Well now we’re getting the effect that the water that is coming up the inner shelf, essentially near shore and up through Norton Sound, has gotten so warm that we’re seeing that push fish out as well. So, we have both a cold-water effect and a warm water effect happening in this region.”

– Lyle Britt

As scientists continue to track these ecosystem shifts in the Bering Sea, a potential species to keep an eye on, the proverbial canary in the coal mine Britt says, is the invertebrate known as a tunicate.

“These tunicates that live on the bottom, in 2010, were in very very high abundance. With each sequential year that we’ve surveyed, with the warming their numbers have dropped precipitously. And these are actually long-lived organisms, they don’t have the ability like fish to just swim to other areas, and so they may be a strong indicator as to what’s going on.”

– Lyle Britt

Although NOAA Fisheries has conducted annual surveys in the Southeastern Bering Sea since 1982, Britt says the funds for next year’s survey are not guaranteed yet. Currently, however, NOAA has partial funding to perform another trawl in the Northern Bering Sea next year.

To view the preliminary findings from the 2019 Northern Bering Sea trawl survey, contact NOAA Fisheries or if you’re in the Norton Sound Region, reach out to Gay Sheffield with Alaska Sea Grant: (907) 434-1149.

Image at top: The Vesteraalen, one of two boats used by NOAA Fisheries to do the bottom trawl survey in the Bering Sea. Photo: Lyle Britt, used with permission.

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