Valuable Crab Populations Are In a 'Very Scary' Decline In Warming Bering Seahttps://phys.org/news/2021-09-valuable-crab-populations-scary-decline.html... The collapse in the Bering Sea snow crab population comes amid a decade of rapid climatic changes, which have scrambled one of the most productive marine ecosystems on the planet in ways that scientists are just beginning to understand. The changes are forcing them to reconsider how they develop models to forecast harvest seasons.
As waters warm, some older crab have moved northwest, young crab are being gobbled up by an increased number of predators and disease is on the rise. All of this could be making crab more vulnerable to excessive harvesting, and that has increased concern over the impacts of trawlers that accidentally scoop up crab as they drag nets along the sea floor targeting bottom-dwelling fish.
The forecast for the 2022 winter snow crab season is bleak. At best, it is expected to be considerably less than 12 million pounds. That would be down from a 2021 harvest of 45 million pounds and a fraction of the more than 300 million pounds taken during two peak years in the early 1990s.
The iconic Bering Sea red king crab, which can grow up to 24 pounds with a leg-span up to 5 feet, also are in trouble. In a big blow to the commercial crabbers, many of whom are based in Washington, the October harvest for these crab has been canceled, something that has only happened three times before.
Most of the king crab harvest and snow crab sold in the United States in recent years has been imported from other countries.
... The Bering Sea king crab fishery has a tumultuous history. The annual catch soared to about 130 million pounds in the early 1980s, then crab stocks crashed and the harvest was shut down. Since 1996, in the aftermath of two consecutive years of closures, the harvests have never topped 22 million pounds, and fell to 2.6 million pounds last year.
Ocean conditions are key for scientists studying the decline of Bering Sea crab, which for all species are now estimated to be at their lowest overall levels in more than four decades.
"This is huge," said Bob Foy, director of the National Oceanic and Atmospheric Administration's Alaska Fisheries Science Center. "It is a massive shift for our ecosystem in the Bering Sea, and the implications for other fisheries are just starting to be thought through."
He notes snow crab juveniles looked to be on an upward trend just two years ago. Then, in the space of 48 months, they appeared to have imploded by 99%.
One focus of research is the Bering Sea ice that forms each winter, and acts like a giant platform for growing algae at the base of the food chain. As it freezes, the ice sheds a dense layer of cold, briny seawater that eventually forms a cold pool on the bottom, prime conditions for young snow crab.
In some recent winters, there has been a big reduction in the extent and thickness of the ice.
During these weak ice years, the size of the cold pool has shrunk, a retreat closely mapped by federal researchers.
One of the crab's voracious predators—cod—do not like the chill temperatures in the cool pool. The warmer temperatures appear to have made it possible for cod to hunt far more young snow crab, according to Fedewa, who said analysis of cod bellies show they are eating more crab.
"The assumption is that the thermal barriers in cold-water habitat that have protected juvenile snow crab from predators like Pacific cod are basically breaking down," Fedewa said.
King crab also may be suffering from increased predation.
Earlier federal research in the 1980s showed that young Bristol Bay sockeye salmon like to feed on larval king crab. In recent years, there have been a series of strong sockeye runs that may be due, at least in part, to warmer and more favorable conditions in the lakes where they rear before heading to saltwater.
The warming trends in the Bering Sea appear to be increasing the numbers of crab found farther north. The trends, tracked through surveys, are not fully understood.
The fall Bering Sea king crab harvest was canceled because of low numbers of mature females.
But this summer's survey found an increase in mature king crab females in more northern areas. These crab were tallied outside the main survey zone, and thus not used to calculate potential harvests.
Snow crab populations also appear to be shifting.
This last winter, crab skippers reported an unusual harvest season when the main concentrations of snow crab were found some 500 miles northwest of Dutch Harbor, which is about twice the typical distance for February and March fishing.
... "Perhaps Bering Sea crab are an indicator species—the proverbial canary in the coal mine. I don't know. But things are changing, of that we can be certain."
