• A retrospective assessment of primary productivity on the Bering and Chukchi Sea shelves using stable isotope ratios in seabirds

      Abromaitis, Grace Elizabeth; Schell, Donald; Castellini, Michael; Springer, Alan (2000-12)
      Recent declines of marine mammal seabird populations in the Bering Sea have raised the question of whether the changes are caused by fishing pressure or a decrease in ecosystem carrying capacity. Stable carbon (¹³C⁾ and nitrogen (¹⁵N⁾ isotope ratios in Thick⁻billed Murre muscle and feathers were used as indicators of changing seasonal primary production. ¹³C values in phytoplankton vary directly with growth rates and are passed up the food web to consumers. Muscle and feather ¹³C values decreased over the period 1976-1998 suggesting a decline in Bering/Chukchi continental shelf primary production. Carbon isotope ratios in murres were correlated with bowhead whale baleen isotope ratios and to some climate indices. In contrast, ¹⁵N values in the birds showed no significant change indicating no concurrent shifts in trophic status.