Implications of multiple ecological mechanisms on the poleward range shift of snow crabs (Chionoecetes opilio) off Alaska

Prof Gordon Kruse1

1University Of Alaska Fairbanks, Juneau, United States

Waters off Alaska have experienced pronounced warming in recent decades. For the first time since summer surveys began in 1982, the eastern Bering Sea had no cold pool (<-1.0 C) of bottom water and experienced the lowest sea ice on record. Likewise, in 2018 the northern Bering Sea had an unprecedented near lack of sea ice and the Chukchi Sea experienced the warmest year on record. Snow crab distribution has contracted north with declining sea ice. Intermittent cool periods have not resulted in a crab redistribution to the south, as their southerly distributions are constrained by northward advection of crab larvae by ocean currents and a large biomass of groundfish predators to the south. Yet, the productivity of snow crab in the northern end of their range is also compromised by several mechanisms. Reproductive output of female snow crab is a function of body size which declines with increasing latitude. Moreover, their reproductive cycle shifts from annual to biennial for temperatures <1.0 C, reducing reproductive output by 50%. Warming has also been accompanied by a rapid northward shift in Pacific cod, a major predator. Although there have been recent large increases in snow crab biomass in the Chukchi and Beaufort seas (Arctic Ocean), those in the Chukchi Sea fail to grow to harvestable sizes under current ecological conditions. In the Beaufort Sea, snow crab may not support viable future commercial harvests, as they are primarily confined to deep waters (> 200 m depth).


Gordon Kruse is a Professor of Fisheries Emeritus from the University of Alaska Fairbanks, College of Fisheries and Ocean Sciences, Department of Fisheries. He has worked on marine fisheries off Alaska for 33 years. He has published more than 100 peer-reviewed publications. Research has focused on applied marine fisheries research, including stock assessment, population dynamics, fisheries oceanography, marine ecosystem dynamics, fishery management, and ecosystem-based fisheries management. He is a co-chair of the Scientific and Statistical Committee of the North Pacific Fishery Management Council, member of the Science Panel of the Exxon Valdez Oil Spill Trustee Council, and one of three US delegates to the Fishery Science Committee of the North Pacific Marine Science Organization (PICES).

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