Surveys portend bad season ahead for Bering Sea crabbers

Surveys of Alaska’s Bering Sea king crab and opilio fisheries are portending another dismal season.

The 2021-2022 red king crab season in the U.S. state was canceled after trawl surveys indicated that the biomass had fallen below the threshold of 8.4 million mature females, a population level not seen since 1994 and 1995, when the fishery was also shut down. Though complete data for the upcoming season’s surveys won’t be out until sometime in September or October 2022, preliminary data from the first of three surveys indicates another season in which crabbers will stay tied to the docks, according to Mark Stichert, a groundfish and shellfish fisheries management coordinator with the Alaska Department of Fish and Game.

“We’re seeing some preliminary information that shows that we’re going to continue to be low in abundance,” Stichert said. “We’re seeing some very similar trends. The number of mature females is going down, and mature males are slightly up. What we’re not seeing is the entry of small crab into the fishery.”

The total allowable catch (TAC) for each species is based upon data gleaned from three phases of trawl surveys conducted in late summer. In the 2008-2009 season, the TAC was set at around 20 million pounds. In the last decade, TACs rose from 7.8 million pounds in the 2011-2012 season to 9.97 million pounds in the 2015-2016 season, then declined. The TAC for the 2017-2018 season was set at about 3 million pounds and the 2020-2021 TAC was 1.2 million pounds.

Given the complexity of the ocean ecosystem, multiple conditions may be responsible for the rapid decline, Stichert said.

“Clearly, there’s no smoking gun,” Stichert said. “We’ve been in this trend for quite some time, and something is preventing the young crab from entering the fishery.”

Among theories considered by biologists are ocean temperature fluctuations and subsequent seasonal sea ice formation changes, which could be having an adverse effect on the survival of larval crabs during the first month or two after they hatch, when they live as pelagics and are subject to the whims of ocean currents.

“Water temperature affects currents, and they may get dropped into a less-complex bottom structure,” Stichert said. That can mean falling into a land of starvation or a land of predators, or both, he said.

The total mass of sea ice in the Northern Hemisphere has declined by 13 percent in the last decade, and the lack of ice has impacted water temperatures. While cold north winds dominated northern regions of the Bering Sea, a prevailing trend of warm, southerly winds have recently prevented ice formation south of Bristol Bay and the Pribilof Islands.

“Ten years ago, it was not uncommon for ice to hit the north side of the Alaska Peninsula as far south as the Pribilof Islands,” Stichert said.

At the same time, oceanographic data notes the shrinking of the “Cold Pool,” a body of water with temperatures of 0 degrees to 2 degrees Celsius. The Cold Pool serves as a barrier separating species such as pollock and cod from the northern reaches of the Bering Sea. Its absence from 2017 to 2019 had a profound effect on species distribution, according to the 2021 Eastern Bering Sea Ecosystem Status Report, put out by the National Oceanic and Atmospheric Administration.

Some of the same ecosystem changes are suspect in the crash of the opilio crab, or snow crab, population in Alaskan waters. Last year the industry had expected a TAC of around 45 million pounds, which would have been similar to 2020-2021, but trawl surveys revealed a 99 percent drop in mature females and a substantial drop in the abundance of mature males.

The North Pacific Fishery Management Council set the TAC for the 2021-2022 season at 12.4 million pounds, but the State of Alaska which jointly manages the fishery, opted for a much-lower TAC and set it at 5.6 million pounds.

“We saw an 80 to 90 percent decline in all sizes within the population,” Stichert said.

The trawl surveys also found more than 50 percent of Pacific cod biomass had migrated to the northern Bering Sea. Those fish are normally held south of the crab-rearing areas by the Cold Pool.

But in its absence, cod moved in and have been blamed for predation on the opilio crab. Another oddity is that the crab had marched westward, into deeper water, suggesting they were looking for colder subsurface sea temperatures.

Though some speculated that the crab traveled outside of the survey areas, scientists who advise the council are convinced the disappearance is linked to a cataclysmic mortality event.

As of 25 July, the two survey vessels had yet to complete transects in the last two areas that encompass the waters around the Pribilof Islands and the northern Bering Sea. But it was doubtful that the missing opilio would show up, and even more doubtful they would appear in enough abundance that would substantiate a profitable TAC for the crabbers, according to Stichert.

“It’s a massive, massive blow to the industry,” Stichert said. “There is lots of uncertainty, and it’s hard to predict where it’s going to end up.”

Reporting by Charlie Ess

Photo courtesy of ASMI/Chris Miller