Why did one billion Alaskan snow crabs mysteriously disappear?

Officials in Alaska have cancelled this year’s snow crab fishing season in the Bering Sea, citing extremely low population levels.

The move is a blow to the state’s crab industry, a major part of Alaska’s economy and a global source of seafood, and comes after a massive and unexplained crash in the crab population.

State officials told CBS News that about one billion crabs have disappeared from the frigid northern waters of the Bering Sea in the past two years. It’s a sudden, drastic and somewhat mysterious drop in population — but one that might also be related to the climate crisis.

“Did they run up north to get that colder water?” one Alaska fisherman, Gabriel Prout, said to CBS. “Did they completely cross the border? Did they walk off the continental shelf on the edge there, over the Bering Sea?”

Snow crabs — a large crustacean with massive legs, native to the northern Atlantic and Pacific oceans — are eaten around the world and fished in Alaska’s coastal waters, among other cold marine habitats.

The Alaska Department of Fish and Game (ADF&G) regularly monitors crab populations and — if populations are too low — they can shut down a fishing season to ensure a species doesn’t die out completely.

In addition to the Bering Sea snow crab season, the department also shut down the blue king crab season around Saint Matthew Island, the red and blue king crab season in Pribilof and the red king crab season in Bristol Bay.

“Understanding crab fishery closures have substantial impacts on harvesters, industry, and communities, ADF&G must balance these impacts with the need for long-term conservation and sustainability of crab stocks,” the agency said in their announcement of the Bering Sea snow crab closure.

No one is exactly sure why the snow crabs have disappeared, but there are some ideas. One researcher with ADF&G told CBS News that disease is one possibility.

But officials are also looking into the impact of the climate crisis on these frigid-water marine arthropods. Water temperatures in the Bering Sea — the stretch of ocean between western Alaska and far-eastern Russia — have spiked in recent years.

Younger snow crabs need cooler water than older crabs, according to the US National Oceanic and Atmospheric Administration (NOAA). And one biologist with ADF&G told NBC News that warmer waters could have forced younger crabs into smaller and smaller pockets of cold water, which could have led those crabs to starve.

Many of the snow crabs in the Bering Sea live around something called the “cold pool”, NOAA says, a mass of water formed from melting sea ice. But if temperatures get too warm for sea ice to form, that cold pool may cease to exist.

In addition, as waters warm, predators like cod could move into snow crab habitat and threaten the crustaceans, NOAA adds.

Gabriel Prout, the Alaska fisherman who spoke with CBS, told the network that the fishermen who rely on the crab season need some kind of relief program to weather difficult crab years, like this year is now set to be.

But if the declines are truly related to warming temperatures, these issues may only get worse in the coming decades.

The planet has already warmed about 1.1-1.2 degrees Celsius above 19th-century temperatures as humans have dumped greenhouse gasses like carbon dioxide into the atmosphere. Much of that heat has ended up in the ocean — water surface temperatures have increased by 0.8C in that time, according to the Woods Hole Oceanographic Institute.

With further temperature increases, sea ice would have even more trouble forming and chilly waters would be pushed even further north, potentially creating even more challenges for cold-water species like the snow crab.