Past heat waves and low sea ice continued to impact Alaskan waters in 2021


The so-called blob that brought warm surface water temperatures to the Gulf of Alaska between 2014 and 2016 has passed.

But the effects of that drop, and a subsequent heat wave in 2019, are not all in the rearview mirror. And researchers are preparing for more, as climate change leads to further warming of the oceans.

“For an area like the Gulf of Alaska, this is definitely something we need to understand better,” said Bridget Ferriss, fish research biologist at NOAA Fisheries. She edited this year State of the Gulf of Alaska Ecosystems Reportused by federal managers to inform fisheries policy in Alaska.

Last year, researchers continued to track the impacts of recent heat waves on Alaskan marine species.

Ferriss said a heat wave occurs when the sea surface temperature on any given day is above 90% of the recorded temperatures for that same day, for five consecutive days.

The Gulf was not dominated by heat waves in 2020 and 2021 as it was in previous years. But some populations are still reacting – for better or for worse.

Forage fish, some seabirds and humpback whales in Prince William Sound all appeared to be experiencing declines in the Gulf related to warm temperatures, with mixed recovery rates.

Herring, on the other hand, have been doing well since the heat wave. They thrive in warmer water.

The salmon was probably also hit by the blob. Ferriss said declines in salmon returns in 2020 would follow low juvenile salmon survival in the years immediately following.

“I think there are definite signs that they’ve been hit by the heat wave,” Ferriss said. “We don’t have a nice concise story yet for really what caused each one.”

NOAA fisheries research biologist Elizabeth Siddon was the editor of the Bering Sea Ecosystem Report. It also takes a long-term view of the impact of conditions over the years on salmon runs.

“A lot of the stories or things that we saw in 2021 were the result of conditions that these organisms – fish or crabs, salmon – have been experiencing since 2014 when this new warm phase started,” she said.

Siddon thought of three coincidental accidents in the Bering Sea – snow crab, salmon and seabirds.

She said it was important to have a historical perspective. To understand salmon accidents in the Arctic-Yukon-Kuskokwim region, for example, one must follow the course of the past few years.

“What we see this year could be the result of what happened this year,” she said. “It could be the result of what happened two or three years ago.”

Scientists monitoring the Bering Sea are studying another important factor: sea ice.

“When the ice melts, we get this cold, dense water that sinks to the bottom of the Bering Sea,” Siddon said. “And that cold water then changes the distribution of fish in the Bering Sea.”

She said when the sea ice was low and there were no cold pools in the years after the surge, so species were freer to move around the northern Bering Sea. Now, she says, NOAA sees different combinations of species living there than they’ve seen in the past.

Reports like those from NOAA are used to inform policy decisions by the board that manages the fishery in Alaska’s federal waters. This group, the North Pacific Fishery Management Council, closed the Pacific cod fishery in 2020 after the blob decimated cod stocks in the gulf.

Ferriss said it’s too early to tell if this species is recovering, years after the fact.

“It is still at a low level since the sea heat wave period,” she said. “And we’re monitoring it and trying to make sure we’re managing this fishery properly so it can recover.”

She said it’s important for researchers and fisheries managers to keep abreast of the impact of changes like these on species in the Gulf because the region is changing so rapidly.

That’s true now, just a few years after gout disappeared. But as heat waves continue to build in the North Pacific, as predicted, it could be more critical than ever.


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