10B Alaskan Snow Crabs Vanished. We Now Know Why

An astounding number of Alaskan snow crabs disappeared from the Bering Sea over the last several years, and scientists say they've finally discovered why. A new paper published in Science blames marine heat waves in 2018 and 2019 for the decimation of 90% of the snow crab population through 2021, around 10 billion of the crustaceans, Smithsonian Magazine reports. The snow crabs died of starvation as temperatures rose, the researchers say. "When I received the 2021 data from the survey for the first time, my mind was just blown," lead author Cody Szuwalski tells 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."

Snow crabs thrive in colder waters, and usually enjoy temperatures below 35 degrees Fahrenheit on the floor of the Bering Sea. While they can survive in warmer waters, up to 53 degrees, they need to eat more when things heat up. "From 2017 to 2018, the calories they needed quadrupled," Szuwalski says, per New Scientist. Unique circumstances made the conditions for the snow crabs, also known as Tanner crabs, worse. A population boom in 2018 meant more crabs were competing for food, and warmer water meant they all needed to consume more of it. Along with snow crabs, fewer salmon, seabirds, and seals were recorded over this period.

"We are now witnessing more and more big crashes associated with extreme temperatures," zoologist Christopher Harley tells New Scientist. "The list of species and ecosystems that are strongly impacted just keeps growing." CNN notes that Arctic temperatures are warming four times faster than other parts of the globe. Species that thrive in warmer waters, like sablefish and walleye pollock, increased as waters warmed, signaling how ecosystems in the region may change as water temperatures rise. As for the snow crabs, it may take four years for specimens of a "fishable size" to show up in the region, according to Science News. Even then, numbers may be small. Szuwalski tells CNN that in the long term, the crabs will likely move north, while "in the eastern Bering Sea, we probably won't see as much of them anymore." (More crabs stories.)