Bering Sea | Climate and Oceanography
Human-induced borealization and the collapse of the Bering Sea snow crab fishery Presenter: Mike Litzow , mike.litzow@noaa.gov, Alaska Fisheries Science Center, NOAA Fisheries Brendan Connors , Brendan.Connors@dfo-mpo.gc.ca, Fisheries and Oceans Canada Lisa Eisner , lisa.eisner@noaa.gov, Alaska Fisheries Science Center, NOAA Fisheries Erin Fedewa , erin.fedewa@noaa.gov, Alaska Fisheries Science Center, NOAA Fisheries David Kimmel , david.kimmel@noaa.gov, Alaska Fisheries Science Center, NOAA Fisheries Trond Kristiansen , trondkr@faralloninstitute.org, Farallon Institute for Advanced Ecosystem Research Michael Malick , michael.malick@noaa.gov, Northwest Fisheries Science Center, NOAA Fisheries Jens Nielsen , jens.nielsen@noaa.gov, Cooperative Institute for Climate, Ocean, and Ecosystem Studies, University of Washington Cody Szuwalski , cody.szuwalski@noaa.gov, Alaska Fisheries Science Center, NOAA Fisheries Eastern Bering Sea snow crab ( Chionoecetes opilio ) went from the highest survey-estimated abundance on record in 2018 (11.7 billion animals) to the lowest on record in 2021 (940 million animals), resulting in the closure of a fishery worth ∼ $250 million in recent years. The collapse coincided with extreme 2018-2019 warming in the Bering Sea. Snow crab are an Arctic, ice-associated species, and borealization (the transition of Arctic ecosystems to a subarctic state) has long been proposed as one of the most consequential outcomes of climate change for Arctic marine taxa. Here, we investigate the role of human-induced borealization as a cause of the snow crab collapse. We combined information from thirteen time series of physical and biological variables to create an index of borealization for the southeast Bering Sea. We then used this index to address three objectives: 1) quantify the relationship between borealization and snow crab abundance; 2) evaluate the role of human activities as a driver of borealization; and 3) estimate the probability of further borealization in current and next-decade climate states as an aid for adaptation decision-making by fisheries stakeholders. Using a Bayesian regression model, we found that the borealization index was statistically related to the mass mortality event leading to the snow crab collapse. We propose that this relationship may be useful for forecasting the snow crab response to either Arctic or subarctic/boreal conditions in the future. Using output from 23 CMIP6 climate models, we also found strong evidence for a human role in Bering Sea borealization, and conclude that the warming associated with 2018-2019 borealization likely exceeded the most extreme warming that would have been possible under preindustrial conditions. Projections from the same set of climate models indicate that 17% of years are expected to produce warming similar to or greater than 2018-2019 in the current climate. This annual risk is projected to exceed 30% by the 2030s or 2040s, depending on emissions trajectories. The rate of Bering Sea warming over these time scales depends heavily on internal climate variability, which precludes a precise projection of the actual rate of extreme warming events. However, these probabilistic risk projections may be useful for adaptation decision-making by stakeholders in the snow crab fishery, and a similar approach may be useful for other fisheries showing acute climate change effects.
Alaska Marine Science Symposium 2023 39
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