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Monday, December 5, 2022

Crustacean Decimation Due to Climate-Change-Driven Cannibalization

Snow crab legs, the pale-pink centerpiece of any self-respecting seafood platter, are no longer on the menu.

They are the victim of a massive population crash that led Alaska to cancel its 2022 Bering Sea snow crab harvest for the first time in history. As fishery officials announced the closure of one of the state’s most lucrative harvests—the Alaskan snow crab industry is worth some $132 million a year—they said that the state’s snow crab population had dropped 87%, from 8 billion in 2018 to a billion last year. Further fishing could wipe out the population entirely.

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Officials suggested that a combination of climate change and some kind of crustacean health crisis might be to blame—Alaska is the fastest warming state in the U.S.. They posited that the warming waters of the Bering Sea forced the cold-loving crustaceans into increasingly small pockets of frigid water, leaving them more susceptible to hunger, disease, and predation. But that’s only part of the story, says Wes Jones, the Fisheries, Research, and Development Director for the Norton Sound Economic Development Corporation, a private nonprofit organization that represents communities in the Bering Sea region and promotes fishing as an industry and livelihood. According to the marine biologists he works with, the most immediate cause of snow-crab death is one that even seasoned fishermen and scientists didn’t see coming: a mass cannibalism frenzy.

To understand what really happened in the icy depths of Alaska’s Bering Sea this year means going back to 2017, when fishermen started reporting an unprecedented population explosion of juvenile snow crabs—what is called, in crabber speak, a “recruit.” The population boom continued into 2018 and 2019, creating what Jones says was the largest recruitment event on record. Jones is something of a local piscine historian. He can quote fishery statistics going back 30 years in the same way a Red Sox fan might quote batting averages. At the time the young crabs were too small for a legal harvest—juvenile snow crabs take four to five years to mature—but there were enough of them for seasoned crabbers to start the count-down to huge hauls starting in 2022.

In the meantime, Bering Sea temperatures, which usually hover around freezing, were on the rise, spiking several degrees between 2017-2019. Unlike mammals, who use less energy when temperatures rise, cold-water fish and crustaceans speed up their metabolism. The faster the crabs grow and expend energy, the faster they have to replace it, says Jones. Some of the crabs may have headed north into cooler Russian waters, but most seem to have stayed put. “All of a sudden you had this huge number of little crabs coming up, eating themselves out of house and home,” says Jones. “Then the water warmed, which meant they had to eat more.” It was a double whammy, he says, and the results were inevitable for a hungry, omnivorous species that has run out of its usual food source: “They basically cannibalized each other.”

Snow crabs are only the latest victim of climate change up in the Bering Sea area. For years, the fishing industry has reported lower-than-usual catches of certain species. But rising temperatures don’t necessarily lead to a steady decline into obsolescence. Just as likely it leads to unpredictable boom and bust cycles for climate change winners and losers that have unanticipated consequences for creatures up and down the food chain. A population explosion of sockeye salmon south of the Bering Sea, in Bristol Bay, is the likely reason for the recent collapse of Alaska’s lucrative red king crab harvest, which was also canceled this year, for the second time in a row. Meanwhile, the warming waters of the historically cold Bering Sea have opened the door for Pacific Cod, a predator of juvenile crabs of all kinds.

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It will be years before the Alaskan snow crab population recovers to harvest-worthy levels, says Jones. And that’s only if temperatures in the Bering Sea stay cool enough for the cold-loving juveniles—and climate change is making everything harder to predict. Scientific projections, he says, are based on what has happened in the past. “But when you start seeing things outside of the range of what you’ve seen before, you don’t know how that’s gonna affect something until it’s happened.” Like rising water temperatures. And cannibalism.

from TIME
via Time.com

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