Scientists say collapse such as Bering Sea crab stocks could happen more often
February 15, 2023
The first-ever cancellation of Alaska’s Bering Sea snow crab harvest was unprecedented and a shock to the state’s fishing industry and the communities that depend on it.
Unfortunately for that industry and those communities, those conditions are likely to be common in the future, according to several scientists who made presentations at the Alaska Marine Science Symposium held in late January.
The ocean conditions that triggered the crash were likely warmer than any extreme possible during the preindustrial period but now can be expected in about one of every seven years, said Mike Litzow, a National Oceanic and Atmospheric Administration scientist based in Kodiak. By the 2040s, those conditions can be expected to occur one out of every three years, he said.
Blame “borealization” for the disaster befalling snow crab, which is an Arctic species, Litzow said. That term refers to an ecosystem becoming boreal, with groups of organisms — called “taxa” by scientists — that have been south of the Arctic until recently.
“If we think about an Arctic animal at the southern edge of its range that’s exposed to really rapid warming, that leads us sort of inevitably to the concept of borealization,” said Litzow, director of NOAA Fisheries Kodiak laboratory and shellfish assessment program. “As you warm Arctic ecosystems, those systems become prone to a state change, where Arctic taxa such as snow crab become replaced by subarctic taxa that are better able to tolerate ice-free and warm conditions.”
Snow crab are dependent on the winter sea ice and the cold conditions created even after the seasonal melt, he said. While they are widely dispersed through the Bering Sea, the sweet spot for the commercial harvest — the place where the crab are big enough to be commercially valuable — is in the southeastern Bering Sea.
But consecutive years of extreme warmth in the Bering Sea, conditions that precluded much ice formation even in winter, kept temperatures above the 28-degree Fahrenheit threshold that is ideal for snow crab — and made the area suitable for sea life from farther south, including groundfish that may prey on juvenile crab, Litzow said.
Though fishery managers are in the process of crafting a detailed plan to rebuild the stock to help harvesters, processors and communities in the short term, in the long term the suitable habitat for snow crab will be farther north, he said.
That points to a need to change management of snow crab and other fisheries, he said. “We really need to start evaluating our risks less on our lived experience and more in terms of the trends going forward,” he said.
Borealization is occurring around the Arctic Ocean and the seas that border it, a product of climate change.
In Alaska’s Bering and Chukchi seas, that means that suitable habitat for Arctic-specialized species like snow crab and fat-packed Arctic cod is shrinking, and lower-latitude species like Pacific cod and pollock are increasingly found at higher-latitude areas, as University of Alaska Fairbanks-led research has detailed. Borealization is happening on land, too, with woody plants growing farther north and animal populations shifting.
For Bering Sea snow crab, which in 2021 dwindled to the lowest abundance of adults observed in the 50-year record, the crash took multiple steps.
The low abundance in 2021 followed what was a record-high population of crab surveyed in 2018. Dramatic increases in ocean conditions forced those snow crabs into a smaller area, said Gordon Kruze, a professor emeritus at UAF’s College of Fisheries and Ocean Sciences. The higher temperatures, combined with a much denser population, increased crab metabolism — so much so that the crabs’ caloric needs in some cases quadrupled, “leading to mass starvation,” Kruze said.
Between snow crab and red king crab closures, losses are not just the nearly $300 million in foregone direct payments that the state has calculated, said Scott Goodman, executive director of the Bering Sea Fisheries Research Foundation. Losses probably amount to at least $1 billion when all multipliers are considered, “which really paints a bleak picture for the industry,” Goodman said at the symposium.
“The reality in Alaska is that major plants that process crab are closing,” he said. “The reality at the community level … impacts are extreme. Entire fleets are tied up.”
One ongoing project, though, offers a glimpse of hope that human intervention could restore the populations in the future.
Chris Long, a scientist working at the NOAA Alaska Fisheries Science Center laboratory in Kodiak, has been experimenting for several years with projects that might show how to enhance natural crab stocks with hatchery-raised larvae. Much of his work focuses on red king crab in Kodiak, a region where the once-thriving king crab fishery crashed in the 1980s and never recovered.
In experiments so far, very few of the larvae have survived after being spread in the water, at best about 2%, he said in his presentation at the symposium. However, that survival rate is not much different from what happens in the wild, where crab larvae are tempting and ideal food for bigger fish.
Legislation passed last session may turn out to help make mariculture-assisted crab fisheries a reality, Long said. The law expanded authorizations for nonprofit hatcheries, adding various types of shellfish to the suite of species that those organizations will be allowed to grow. It also created a framework for the state to regulate cultivation of those shellfish.
If the process works, crab enhancement projects are more likely to get industry funding, thanks to the new legislation, Long said.
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