The snow crab population in the Bering Sea off the western coast of Alaska has fluctuated for decades. An increase in young crabs back in 2018 gave way to optimism that fishing would be good for years to come, but the hope was short-lived.
Gabriel Prout and his family own the fishing vessel Silver Spray in Kodiak, Alaska.
He said it was obvious something was wrong the last few years. The Bering Sea fishing grounds are usually covered in sea ice in the winter. But there wasn’t much ice, and they fished further north than usual. Finding snow crabs was still difficult.
“It was just very poor fishing,” said Prout. “We searched for miles and miles and miles and really didn’t see anything.”
More than 10 billion Bering Sea snow crabs disappeared in Alaska between the years 2018 and 2022, devastating a commercial fishing industry worth $200 million just last year. The population crash coincided with a marine heat wave that hit the Bering Sea. Now, fishermen and researchers are working to figure out what happened, and they think warmer ocean water could be to blame.
Bycatch, which is the catch of a non-target species, has also drawn criticism from fishermen for its effect on the snow crab fishery. Even with the fishery closed to crabbers, the bycatch limit for the trawl sector is 3.6 million individual snow crabs this season.
But such a large, sudden die-off and the lack of sea ice was a red flag for scientists like Erin Fedewa, a research fishery biologist with the National Oceanic and Atmospheric Administration.
“That was an immediate potential smoking gun when we saw this Arctic species suddenly in decline,” she said.
That’s because sea ice is an important ingredient in the snow crabs’ life cycle. In the winter, it accumulates on the water’s surface. And during the summer, the ice melts, sending cold, dense water sinking to the ocean floor, where it hovers just above freezing at around 35 degrees.
Scientists call it the cold pool, and it’s a sanctuary for young crabs. Warmer temperatures can lead to starvation, and higher rates of disease. At the Kodiak Fisheries Research Center, state and federal researchers are piecing together how all those factors contributed to the crabs’ collapse.
Tanks filled with seawater pumped in from the bay replicate conditions on the seafloor.
“And then we can hold the different portions of the same population in, say, five degrees Celsius, eight degrees Celsius. And we can begin to look at the response of those species once they’re in these warmer temperatures,” said Fedewa.
Scientists use the pools to study how different temperature and pH levels affect the crabs’ development – how fast they grow and how quickly they die.
“We know that increases in temperature increase metabolic rates of fish and crab, causing them to need to eat more and more,” said Fedewa.
In a shrinking cold pool, that means more crabs pushed into the smaller space, fighting for less food. Across the hall from the federal lab, Ben Daly, a research coordinator with Alaska’s Department of Fish and Game, is also trying to figure out how a smaller cold pool affects crabs in the Bering Sea.
“That’s part of what we’re doing now is trying to untangle the what happened part. That’s only half of the challenge. The other half of the challenge is what do we do next,” he said.
His team has been tagging crabs in the wild with satellite transponders that will track their movement over time. He’s hoping the tags provide more detailed information about the distribution of crabs across the cold pool.
And in March, a group of state and federal researchers headed out on the Silver Spray to continue studying crab populations outside the lab. Federal scientists complete population assessments in the Bering Sea annually in the summer.
Ahead of the trip, Gabriel Prout said this winter survey is a big step in understanding more about the species overall.
“We’ll be doing 20 days of pot survey and pot pulling, measuring the crab, sexing the crab, and sizing the crab,” he said.
And tagging the crabs with Daly’s satellite transponders.
Prout and his family are grateful for the work. The many fishermen that rely on snow crabs for income are left with more questions than answers right now.
“We’re sitting tight trying to count our pennies and figure out how to make our way forward,” Prout said.
Scientists say it will likely take years before the snow crab population rebuilds – if another marine heatwave hits the Bering Sea, it could be even longer. But they’re hopeful that lessons learned from snow crabs might provide insight into how other marine species handle climate change as the ocean warms.
This story was created in collaboration with NOVA with major funding from the Corporation for Public Broadcasting.