The effects of windchill exposure on the snow crab, Chionoecetes opilio

Thesis (M.S.) University of Alaska Fairbanks, 2001Millions of snow crabs, 'Chionoecetes opilio, ' are aerially exposed during sorting in the annual Bering Sea commercial fishery. A laboratory experiment measured snow crab responses to windchill exposure. Crabs were exposed to 8 to 16 m/s windspeed and air temperatures from -2 to -10 C̊ for 5 minutes. Mortality, autonomy, and righting response were assessed for seven days post-treatment. Crabs experienced 40% to 100% mortality at windchill from -10 to 16 C̊. Reduced exposure time significantly reduced mortality. Autonomy was variable but pronounced below -10 C̊ windchill. The righting response was impaired after all but the least severe treatment. Estimates of mortality of discarded snow crab in 1998 were calculated from deadloss of retained crab, a windchill model, and a temperature/windspeed model. No relationship existed between catch deadloss and the windchill conditions when the crabs were caught. Mortality of non-retained snow crab was estimated at 3.6% by the windchill model and 19.6% by the temperature /windspeed model

First-Year Survival of Northern Fur Seals (Callorhinus ursinus) Can Be Explained by Pollock (Gadus chalcogrammus) Catches in the Eastern Bering Sea

The Pribilof northern fur seal (Callorhinus ursinus) herd in the eastern Bering Sea has declined by ~70% since the 1970s, for elusive reasons. Competition for pollock (Gadus chalcogramma) with the commercial fishery has been suspected as a contributing factor, but no correlative relationship between fishing activity and fur seal population declines has heretofore been demonstrated. Here, we present evidence for a moderately strong inverse relationship between fishery catches of pollock and first-year survival of fur seals, based on three different approaches to evaluation. We suspect this relationship results from the dependence of lactating female fur seals on locating dense and extensive schools of pollock near the Pribilof Islands to efficiently provide nutrition for their pups, because the pollock fishery also targets these same schools, and when fished, the remnants of these schools are fragmented and dispersed, making them more difficult for fur seals to locate and exploit. Inadequately fed pups are less likely to survive their initial independent residence at sea as they migrate south from the Pribilof Islands in the fall. Our results imply that pollock catches above ~1,000,000 t within ~300 km of the Pribilof Islands may continue to suppress first-year survival of Pribilof fur seals below the estimated equilibrium survival value of 0.50, leading to continued decline of the population