Stable carbon and nitrogen isotope patterns in baleen from eastern Arctic bowhead whales (Balaena mysticetus)

Previous measurements of naturally occurring stable isotopes of carbon (delta13C) and nitrogen (delta15N) along the baleen plates of western Arctic bowhead whales (Balaena mysticetus) have provided a continuous lifetime record of the feeding or nutritional ecology of these animals that migrate annually between isotopically different foodwebs. However, virtually nothing was known about isotopic patterns of eastern Arctic bowheads. We measured delta13C and delta15N values along the baleen plates of three eastern and one western Arctic bowhead whales taken from Canadian waters in 1988 and 1996. In contrast to western Arctic animals, we found strong evidence for periodic fluctuations in delta15N but not delta13C values in the eastern Arctic specimens. We interpret these results as evidence that eastern Arctic animals do not move between foodwebs that differ in delta13C signature and suggest that these whales either (i) move annually between areas isotopically enriched in 15N but not 13C, (ii) shift diet annually by about one third of a trophic level, or (iii) undergo seasonal fasting that results in enrichment of baleen delta15N resulting from protein catabolism.