What made billions of snow crabs disappear from the Bering Sea?

Snow crabs in the Bering Sea once numbered in the billions. But after a recent and massive population crash the crabs have all but vanished from these waters — and they may not be coming back anytime soon.

In 2018, about 3 billion mature snow crabs (Chionoecetes opilio) inhabited the Bering Sea along with roughly five billion iMMAture crabs, the Seattle Times reported. But by late 2021, those numbers hovered around 2.5 million and 6.5 million, respectively — a loss of nearly eight billion crabs in just three years. In February, the National Marine Fishing Service issued an official overfishing notice for the population, and in early October, officials at the Alaska Department of Fish and Game (ADFG) made the difficult decision to cancel the season's snow crab harvest for fear of wiping out the crustaceans altogether.

“Management of Bering Sea snow crab must now focus on conservation and rebuilding given the condition of the stock,” ADFG representatives said in a statement. The agency also canceled the fall harvest of Bristol Bay red king crabs (Paralithodes camtschaticus), due to low survey numbers. 

Miranda Westphal, an area management biologist with the Alaska Department of Fish and Game, called the decision "tremendously difficult." 

"It came after a lot of sleepless nights and a lot of tears. It was one of the hardest decisions we've ever had to make," she told Live Science

What caused the snow crab crash? The main culprit was almost certainly human-caused climate change, though unsustainable fishing practices may also have played a role, the Seattle Times reported.

Snow crabs thrive in the cold northern waters of the Bering Sea floor. For these crabs, water temperature isn’t just a matter of comfort; it plays a critical role in their lifecycle. As seawater cools, it becomes less salty and less buoyant, causing it to sink to the bottom of the ocean. Marine biologists refer to this chilly layer of water as the "cold pool, according to the National Oceanic and Atmospheric Administration (NOAA). Many fish and other types of marine life avoid the cold pool, but for juvenile snow crabs, it’s a sanctuary. With virtually no predators willing to venture into this layer's frigid waters, young crabs can grow up in peace.