Scientists point to climate change as likely cause for Alaska snow crab decline

Even as scientists are still trying to figure out why the Bering Sea snow crab stock crashed in 2021, federal managers are working on a plan to help rebuild it.

The North Pacific Fishery Management Council last week voted to accept alternatives for analysis on its snow crab rebuilding plan — a middle step before implementing an actual plan that will change fishing regulations or openings. The council is on track to approve a final plan for action in December, which would then go to the Secretary of Commerce and through the federal regulation process before becoming official.

Data from last year’s survey at this point seems to confirm that there was a massive decline in the number of young snow crab in the Eastern Bering Sea — something like 99% fewer female snow crab showed up in the survey from 2021.

There’s no complete consensus about why the stock crashed in the first place. Increasingly, however, the models seem to indicate that it’s due to temperature increases linked to climate change.

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In a presentation to the council on June 10, Mike Litzow, the lab director for the National Marine Fisheries Service lab in Kodiak, told the council that researchers have run some models on what he called the “borealization” of the southeast Bering Sea, which is the conversion of the Bering Sea from an Arctic ecosystem to a subarctic ecosystem in the face of increasing ocean temperatures.

“The current understanding in climate science is that you cannot get the Bering Sea as warm as it was in 2014–2020 in a preindustrial ocean,” Litzow said. “We’re seeing the effects of global warming playing out in the Bering Sea.”

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The Bering Sea experienced abnormally high temperatures for several years in a row, notably in 2015-2016 and in 2019, though the last few years have been colder than usual, as well. Overall, climate modelers are showing that extreme temperatures in the Bering Sea are likely to become more frequent, though just how frequent depends on the level of continued carbon emissions.

Of all the models to explain the high mortality, high temperatures seemed to correlate best, Litzow said. It doesn’t explain the exact mechanics of why the temperature variations seem to be correlated with higher crab deaths, but one thing that does show up is that the stress seems to be when higher temperatures continue for a few years. Litzow stressed that there isn’t a good population dynamic model for snow crab and they still need more data.

“It was when we saw those multiple years (of abnormally high temperatures), from 2018, 2019, 2020, that we got the apparent collapse of the stock and the apparent mass mortality of snow crab,” he said. “With the very little information that we have, it does appear that multiple-year events are more deleterious for the population than individual-year events.”

Another cause that some fishermen have indicated is predation on young crab from increasing numbers of Pacific cod in the Bering Sea. However, a report from the council’s Crab Plan Team for its June meeting noted that most of the crab missing from the survey were thought to be above the size range vulnerable to being eaten by Pacific cod.

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Bitter crab disease, a common disease caused by a parasite, was also noted as one potential cause for the massive uptick in mortality. But that, too, doesn’t seem to pan out — the Crab Plan Team report notes that the peak in observed bitter crab disease doesn’t match the timing of the decline.

Finally, a common outcry has been against the trawl fleet, which does take crab as bycatch in the Bering Sea. Scientists in the Crab Plan Team also note that “the declining trend in observed bycatch … seems to match poorly with the snow crab decline.” That doesn’t account for all unobserved mortality, such as bottom trawling gear contacting and damaging soft-shell crabs; researchers are still working on modeling for this population.

The council accepted two alternatives for further analysis in a final rebuilding plan. One is a no-action, which wouldn’t be allowed but is required to be considered; the other would specify a rebuilding time, either with or without a fishery targeting snow crab. Bycatch would be allowed in either case. The council is also looking for more information on some specifics, including what it would be like to remove the floor set for bycatch and counting all crab caught as bycatch throughout their range toward the bycatch limit.

Both of those came at the urging of the industry. Multiple fishermen and representatives asked the council to consider allowing a slightly longer time frame for recovery, which might allow for a limited fishery targeting snow crab. The council was initially discussing setting a recovery period of within ten years, but some commenters urged them to stretch that out to allow some flexibility for a fishery. If the council allowed the recovery time to stretch out longer, it might allow for more fishing, which could help prop up the industry.

Jaime Goen, the executive director of the Alaska Bering Sea Crabbers, told the council that the crab industry is reeling from the revenue loss both in the snow crab fishery and the complete closure of the Bristol Bay red king crab fishery this year. What hurt was the suddenness — a few years ago, the crab stocks were looking hopeful and like a good investment, and many business people and crew members bought in with the hopes those investments would pay off, she said.

“Now those same people are facing bankruptcy,” she said. “This is unprecedented in the United States for a mature, rationalized fishery to suffer a stock collapse, in part due to climate change. We risk losing the resource and the crab industry if the council does not act swiftly and aggressively to rebuild crab stocks.”

The municipalities in the Bering Sea also feel the loss of the crab fisheries. Frank Kelty, representing the city of Unalaska, urged the council to consider options that would allow for a directed fishery because of the ripple effects throughout a community, including on the crab industry.

St. Paul Island, one of the Pribilof Islands and a major location for crab processing and refueling for the fleet, relies heavily on crab as well. The Central Bering Sea Fishermen’s Association is expecting about a 65% drop in revenue due to the crab quota cuts, according to representative Heather McCarty. Mateo Paz-Seldan, representing St. Paul, echoed Kelty, saying the community depends on the revenue from the crab fishery to keep services running for the several hundred year-round residents there.

“There are no other sources of revenue for the community to keep the lights on and provide municipal services,” he said.

The council accepted the motion unanimously, and is scheduled to revisit the snow crab issue in October.