10 Billion Crabs Suddenly Vanished From the Bering Sea. Now We Know Why.
About 10 billion snow crabs disappeared from the Bering Sea between 2018 and 2021.
A recent study concluded that warmer water temperatures helped drive the crabs to starvation.
Experts believe that the crabs will soon start heading farther north toward colder climates.
When scientists realized that nearly 10 billion snow crabs had gone missing from Bering Sea between 2018 to 2021, they weren’t sure where they could have gone. After searching for a potentially migrating population, however, they came to a much more unfortunate conclusion.
A new study published by National Oceanic and Atmospheric Administration (NOAA) researchers in Science found that the billions of snow crabs weren’t finding a new home—they were suffering from what was likely the largest mortality collapse known to the species. Researchers have been aware of the crabs’ disappearance for a while, but the extent of the catastrophe and the exact causes behind it were previously unknown.
“When I received the 2021 data from the survey for the first time, my mind was just blown,” Cody Szuwalski, lead author of the study and fishery biologist at NOAA, told CNN. “Everybody was just kind of hoping and praying that that was an error in the survey and that next year you would see more crabs. And then in 2022, it was more of a resignation that this is going to be a long road.”
The NOAA team started a search for the crabs—looking north, west, and even deep in the ocean. With no evidence of crab migration, the researchers determined that the creatures had been lost to a massive mortality event.
“It’s a fishery disaster in the truest sense of the word,” Szuwalski, told Science News.
While the team soon concluded that warm water was the root cause of the die-off, the Bering Sea temperatures didn’t cook the crabs alive. The study reports that even though snow crabs typically live in water temperatures no more than 2°C, they can easily handle upward of 12°C.
Kerim Aydin, study co-author and fisheries research biologist with NOAA, says that a two-year marine heat wave that kicked off in 2018 sparked a two-pronged attack on the snow crabs. Not only did the warmer temperature push the crab’s caloric needs higher—the crabs sometimes needed as much as four times their normal caloric intake to survive—but it also drew other fish into the water to feed on the crabs’ food supply. The warmer water even invited in species like the Pacific cod that prey on the snow crab.
“This was a huge heat wave effect,” Aydin says, according to CNN. “When the heat wave came through, it just created a huge amount of starvation. Other species may have moved in to take advantage of it, and then when the heat wave passed, things are maybe a bit more back to normal—although the crabs have a long road to getting past that even in normal times.”
And with already booming crab populations that reached record highs in 2018—which caused overcrowding on the eastern Bering Sea shelf that houses the species— an accelerated metabolism left the creatures with a dire food shortage. More hungry crabs in a smaller area, coupled with increased competition from other species, equaled a disaster-in-waiting for the snow crabs.
“Calculated caloric requirements, reduced spatial distribution, and observed body conditions suggest that starvation played a role in the collapse,” the study authors write. “The mortality event appears to be one of the largest reported losses of motile marine macrofauna to marine heatwaves globally.”
And the conditions that caused this catastrophic population collapse are only becoming more common due to climate change. “Climate change is the next existential crisis for fisheries,” the authors wrote in their study, “and snow crab are a prime example for how quickly the outlook can change for a population.”
Bering Sea warming, in particular, is running rampant—the area is warming up to four times faster than warming across the globe—and ice coverage in 2018 and 2019 was at times just 4 percent of a normal year in the region. “This was kind of an unexpected, punctuated change in their populations,” Szuwalksi tells CNN. “But I think long term, the expectation is that the snow crab population will move north as the ice recedes and in the eastern Bering Sea we probably won’t see as much of them anymore.”
Hopefully, the population can recover in another area, and we won’t have to see another die off of billions of animals any time soon.
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