Northern Bering Sea saw some indicators of health rebound in 2023

The health of the Northern Bering Sea has been slowly rebounding after a series of especially warm years.

That was one takeaway from the 2023 Eastern Bering Sea Ecosystem Status Report, which was presented in a Strait Science lecture last week.

Elizabeth Siddon, who is the Ecosystem-Based Fisheries Management lead at NOAA’s Auke Bay Labs in Juneau, discussed the results. These annual reports are intended to look at the overall health of the region’s marine ecosystem and to influence the decisions of the North Pacific Fisheries Management Council.

The Bering Sea in 2023 was cool compared to recent warm years, but it is still warmer than the average temperature of the last 40 years.

The sea ice also had a late start in forming last winter, which has been a common feature as the Arctic warms. However, last year’s ice came about a month later than the ice formed a year earlier. Siddon said this could be partially attributed to Typhoon Merbok which brought early fall warmth to the region and stirred up the water column.

Siddon explained that scientists are interested in looking at sea ice presence because “it changes the vertical structure of the water column.”

For example, as sea ice is forming, salts are being extruded from the ice and increasing in salinity of the water.

“At the southern extent in the spring, when that ice melts, it’s fresh water that is released into the surface waters, and this in a local sense decreases salinity,” Siddon said.

Changing levels of salinity can change the habitats of fish and phytoplankton. Sea ice also determines the extent of cold water at the seafloor, which acts like an environmental barrier that keeps some species like pollock out.

“What we call the ‘cold pool’ is sort of a footprint of where sea ice was the previous winter,” Siddon said.

The cold pool nearly disappeared amid marine heatwaves in 2018 and 2019. But researchers conducting the bottom trawl survey for NOAA over the last few years have documented its return.

The ecosystem report was split between the Northern Bering Sea— which includes Norton Sound and goes from 60 degrees north latitude to the Bering Strait—and the Southeastern Bering Sea, which covers the area down to the Aleutians.

In the Southeastern portion, the algae, phytoplankton and other organisms at the bottom of the food chain continued their trend of longterm decline, Siddon said. At the next level of the food chain, zooplankton like krill were found in low to moderate abundance.

Pelagic fish found in the water column were in mixed health, but overall, many species seemed to be in bad shape.

For example, the condition of young pollock has been below average since this period of especially warm years began in 2014.

“Even though it cooled for 2022 and 2023, we haven’t seen the fish condition come back like we would think under cooler conditions,” Siddon said.

Juvenile salmon across all species have also been in below-average body condition over the southern continental shelf.

Still, there were some higherthan-average metrics of ecosystem health. For example, sockeye salmon have had high returns for Bristol Bay since 2015.

These same ecosystem health indicators were also down overall for the Northern Bering Sea, but the region seemed to bounce back better from those warm years than the Southeastern Bering Sea, Siddon said.

“The Northern Bering Sea has also cooled and it seems like some of the biological things—the zooplankton and the fish condition—have done better or maybe rebounded faster than the southern Bering Sea for the kinds of time series that we had to look at,” she said.

While the abundance and quality of organisms at the base of the food web was also low in the Northern Bering Sea, the region saw a boost in zooplankton abundance.

And while salmon runs have been down across the region, the condition of juvenile salmon of all four species was positive in 2022; in 2023, there were some slight improvements in the indicators for Chinook and chum salmon, according to the report.

Another part of the report mixed observations from Indigenous experts and scientists on the recent Western Alaska salmon crashes.

“The idea was to look at 2023 and try to explain why we are seeing these big really collapses of salmon runs in the Yukon and Kuskokwim when Bristol Bay sockeye has been doing so well,” Siddon said.

Using data from the previous 15 years, scientists had observed that 2019, the year with the warmest water, the marine juvenile salmon they sampled had the lowest stomach fullness.

“These fish are not finding a lot to eat in 2019,” Siddon said.

Western science offered one explanation for the poor salmon returns, but members of the Kuskokwim River Inter-Tribal Fish Commission encouraged fisheries managers to look at the bigger picture.

A quote from one of their members was included in the report: “There’s the climate change part, there’s bycatch and things like that. And then not only the ocean life, but also what’s happening in our spawning rivers. The health of those because of climate change; too much snow, not enough snow, too cold, too warm. How different everything is changing. I think there’s a lot of things that come into play.”

Siddon and her colleagues will be looking at data collected throughout the year for their 2024 report. Amid an El Niño year, some researchers were concerned that the Bering Sea region would see warmer conditions that would delay sea ice formation. In early December, the ice was still scant in the Bering Strait.

“December cooled off, winds came from the north, sea ice was able to form,” Siddon said. “But the thickness of it was pretty thin and sort of vulnerable to changes in the winds.”

Ice concentration maps from Jan. 16 showed that there were still areas of open water and low ice concentration in parts of the Bering Strait region, such as in Norton Sound.In early December, the ice was still scant in the Bering Strait. However, by the end of the month, it extended south to St. Lawrence Island.

“It’s very mobile and changing fast right now, but it’ll be interesting to see what will come in the next week as the winds change back around.”