Trophic ecology of bowhead whales (Balaena mysticetus) compared with that of other arctic marine biota as interpreted from carbon-, nitrogen-, and sulfur-isotope signatures

In this study, stable carbon (delta(13)C), nitrogen (delta(15)N), and sulfur (delta(34)S) isotope ratios were measured in muscle tissue from the Bering-Chukchi-Beaufort Sea population of bowhead whales (Balaena mysticetus; n = 84) and various marine biota between 1997 and 2000. In previous investigations, stable carbon and nitrogen isotope ratios in baleen from this population have been used to elucidate age, migratory behaviour, and feeding ecology. However, information on delta(13)C, delta(15)N, and delta(34)S isotope patterns in bowhead whale muscle tissue and variability within the Bering Sea population is limited. Stable sulfur isotope values did not vary with delta(13)C enrichment for three consecutive seasons (n = 53) and this suggests that habitat selection by bowhead whales was consistent over the sampling period. We found that in contrast to other studies, seasonal differences (spring versus fall) in delta(13)C values were not associated with seasonal changes in delta(15)N values, suggesting either that bowhead whales maintain a consistently lower trophic position relative to other marine mammals or that stable carbon and nitrogen isotope fractionation is tissue-dependent and (or) isotope-dependent within this species. Seasonal fluctuation in delta(13)C values was consistent for all age classes of bowhead whales and suggests that the Bering and Beaufort seas are both important regions for feeding.