Calanus on the Bering Sea shelf: probable cause for population declines during warm years

Recent observations indicate that climate warming over the southeast Bering Sea shelf may negatively impact commercial and subsistence fish stocks by lowering abundance of large lipid-rich populations of Calanus. Warmer temperatures may impact Calanus by increasing metabolic rates and by altering food resources. We used published laboratory measurements on Calanus finmarchicus to develop a stage-specific individual base model to determine if Calanus populations on the southeastern Bering Sea shelf decline during warm years because of insufficient food concentrations, or because warmer winter temperatures elevate their metabolism during diapause, causing them to exhaust their lipid reserves before the onset of spring production. Results indicate that Calanus can reach its maximum size during both cold and warm years, but during warm winters, they will exhaust their lipid reserves during diapause by the end of December. During cold years Calanus can last into May of the following spring. Ice algae may provide a rich food source in March and April during cold years, before the spring phytoplankton bloom in May. Loss of Calanus on arctic and subarctic shelves may impact fish stocks which depend on Calanus for food.