Why billions of snow crabs disappeared from the Bering Sea

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• Geoff Bennett:

  The Bering Sea snow crab season was canceled this year after billions of crabs disappeared, devastating Alaska's commercial fishing industry and the livelihoods of those who depend on it.

  From Alaska Public Media and KMXT in Kodiak, Kirsten Dobroth reports, fishermen and researchers are working to figure out what happened. Her story was produced in collaboration with "NOVA," with major support from the Corporation for Public Broadcasting.

• Kirsten Dobroth:

  The snow crab population crashed in Alaska, but why? More than 10 billion snow crabs disappeared in 2022, devastating a commercial fishing industry worth $200 million the year before.

  Now researchers are working to figure out what happened. And they think warmer ocean water could be to blame. 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 led to optimism that fishing would rebound, but the hope was short-lived.

• Gabriel Prout, Crab Fisherman:

  It was just very poor fishing. We searched for miles and miles and miles and really didn't see anything.

• Kirsten Dobroth:

  Gabriel Prout and his family own the Silver Spray in Kodiak, Alaska. He says 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.

  The lack of sea ice was a red flag for scientists like Erin Fedewa, who is studying the conditions in the Bering Sea that led to the massive die-off.

  Erin Fedewa, National Oceanic and Atmospheric Administration: That was an immediate potential smoking gun when we saw this Arctic species suddenly in decline.

• Kirsten Dobroth:

  That's because sea ice is an important ingredient in the snow crab's 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.

• Erin Fedewa:

  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.

• Kirsten Dobroth:

  Scientists use the pool to study how different temperature and pH levels affect the crabs' development, how fast they grow and how quickly they die.

  In a separate, smaller tank, researchers hook up monitoring equipment to individual crabs and track their breathing in different conditions. They also take blood samples.

• Erin Fedewa:

  We know that increases in temperature increase metabolic rates of fish and crab, causing them to need to eat more and more.

• Kirsten Dobroth:

  In a shrinking cold pool, that means more crabs pushed into a smaller space, fighting for less food.

  Across the hall from the federal lab, Ben Daly is also trying to figure out how a smaller cold pool affects crabs in the Bering Sea.

  Ben Daly, Alaska Department of Fish & Game: That's part of what were 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?

• Kirsten Dobroth:

  Daly and his team have 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 this winter, a group of state and federal researchers are heading out on the Silver Spray to continue studying Bering Sea crab populations outside the lab. Gabriel Prout and his family are grateful for the work. The many fishers that rely on snow crabs for income are left with more questions than answers right now.

• Gabriel Prout:

  Yes, We're sitting tight trying to count our pennies and figure out how to make our way forward.

• Kirsten Dobroth:

  Scientists say it will likely take years before the snow crab population rebuilds. If another marine heat wave 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.

  For the "PBS NewsHour," I'm Kirsten Dobroth in Kodiak, Alaska.