New estimates of weight-at-size, maturity-at-size, fecundity, and biomass of snow crab, Chionoecetes opilio, in the Arctic Ocean off Alaska

Abstract

Snow crab (Chionoecetes opilio) were identified as a potential future target fishery species in federal waters of the Arctic Ocean off Alaska by the Arctic Fishery Management Plan (Arctic FMP) in 2009, but this plan currently prohibits commercial harvest until sufficient information is available to assess a sustainable commercial fishery. One drawback of the current Arctic FMP is that critical population and biomass estimates were based on limited data. Collaborative research efforts in the Chukchi and Beaufort seas over the past decade have yielded a much richer database on snow crab in the Arctic. Using these data, we generated new estimates of weight-at-size, maturity-at-size, fecundity, and biomass to recalculate sustainable yield of snow crab in the U.S. Arctic. Weight-at-size was generally similar for male and female snow crab between the Chukchi and Beaufort seas, with males reaching overall larger sizes than females in both seas and largest male crabs occurring in the Beaufort Sea. Compared with snow crab in other geographic regions, 50% morphometric maturity was reached at a slightly smaller size in the Chukchi Sea; low sample sizes in the Beaufort Sea prevented maturity-at-size analysis. Fecundity-at-size in the Chukchi Sea was similar to known values estimated for snow crab in other regions. Estimated total reproductive output, using fecundity estimates obtained here, suggest that local reproduction may be sufficient to account for a large portion of observed small juvenile benthic snow crab abundances; further investigation is warranted to determine whether Chukchi and Beaufort populations are self-sustaining at this time. Although snow crab had high abundances in the Chukchi Sea, harvestable biomass of male snow crab only occurred in the Beaufort Sea because crab larger than the minimum marketable size (≥ 100 mm carapace width, based on Bering Sea metric) were absent in the Chukchi Sea over the study period. Our biomass estimates in the Chukchi Sea were substantially higher than previous estimates, owing at least in part to high abundances of small crab that were greatly under-sampled with the large-mesh gear such as was used in surveys referenced in the Arctic FMP. Estimates of biomass and sustainable yield for the Beaufort Sea were over twice as high as previous estimates in the Arctic FMP, but harvestable biomass was largely limited to the slope (> 200 m depth) and is unlikely to support commercial harvest. Our results expand overall understanding of arctic snow crab dynamics in light of potential future fisheries or other, non-fishing activities and inform the management of the Alaskan Arctic stock.