In 2018, when the AFD&G, which regulates Alaska’s fisheries, recorded the largest ever increase in the number of juvenile snow crabs in the Bering Sea, the expectation was that the industry had banner years in store for it once they matured. Something, however, has happened in the waters off of Alaska’s coasts, and no-one is quite sure why, but the crabs have all but disappeared. For the first time ever, the state, last week, said there would be no winter snow-crab season in the Bering Sea. Similarly, the fall Bristol Bay red king crab harvest will not happen for a second year running.
Disease could have caused what an AFD&G official has described as “the biggest crash we’ve ever seen in snow crab”, but, for now, the main suspect is a spike in water temperatures in 2019 that could have driven crabs further north. That year, the number of crabs was in line with the 2018 figure. The pandemic forced the 2020 census to be called off, so when state biologists returned in 2021, they were astounded to see that 90% of the crabs had disappeared.
That warmer water temperatures and, ultimately, global warming are to blame would seem to be an open-and-shut case, but the evidence, for now, is only circumstantial: measurements compiled by Noaa, a federal science agency, show that temperatures in Alaska are rising faster than they are in any other US state. Offshore, that is causing the loss of billions of tonnes of sea ice each year. As it goes away, the water warms and the cold-water-loving snow crabs, it stands to reason, scientists say, are being affected. They just aren’t sure how.
Data recorded between 1982 and 2018 as part of the monitoring being done by the EPA, America’s environment agency, of the impact of rising temperatures, suggest northward migration is a plausible explanation. Today, the populations of not just snow crab, but also Alaska pollock and Pacific halibut, now find their greatest concentrations some 30km further north than in 1982. The trend is corroborated by similar monitoring of species in the waters off America’s north-east. That data, which stretch back to the 1970s, find that the three species monitored there (American lobster, red hake, and black sea bass) appear to have moved north by 180km.
Water temperature, according to Noaa, is not the only factor that can cause populations of marine animals to shift. Other factors could include interactions with other species, harvesting pressures, ocean-circulation patterns, habitat change and species’ ability to disperse and adapt. As a result, the northward migration may have been the result of something other than — or more than just — warmer temperatures.
But even if the cause remains uncovered, the outcome is plain enough; for fishermen, this season is a bust, and may bankrupt even some long-time fishing operations. For the state, having the snow-crab population fall below the level the ADF&G requires for quotas to be issued, meant that, instead of managing a population boom, it was, according to a 10 October announcement, now shifting its to “conservation and rebuilding”.
Kevin McGwin, PolarJournal
Featured image: Alaska Bering Sea Crabbers
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