Sulfur stable isotope ratios provide further insight into movements of the fin whale, an oceanic long-range migrant

Abstract

Stable isotope ratios have proven a valuable tool to investigate marine mammal ecology, including diet, distribution, and migratory movements. While most studies have focused on δ15N and δ13C values, δ34S values have been little used because their pattern of variation and tissue dynamics remain unclear. We examined the sequential variation of δ15N, δ13C, and δ34S values along the baleen plates from fin whales occurring off West Iceland in summer. All baleen plates exhibited fluctuations along their growing axis. A significant synchronic correlation was found between δ15N and δ34S values, while the relation of these values to the δ13C value was highly variable and inconsistent. These results were similar to those obtained in previous studies of Greenland bowhead whales, although the pattern of the oscillations in fin whales showed an increase in values during winter, while those of bowhead whales showed a decrease. Although seasonal variations in food intake and the associated cycles of protein synthesis and catabolism may have played a role in such fluctuations and the observed differences between species, we suggest that the main driver for the δ34S fluctuations reflected in baleen plates is the variation of local baselines between winter and summer grounds. This suggests ample potential for using δ34S values to study migratory movements and destinations of marine megafauna, provided that the geographic variation in δ34S baselines is clarified.