Feeding ecology of dusky dolphins Lagenorhynchus obscurus: evidence from stable isotopes

The dusky dolphin Lagenorhynchus obscurus occurs in the Southern Hemisphere, where it is restricted to coastal temperate areas. This study aimed to characterize the feeding ecology of dusky dolphins inhabiting northern and central Patagonia by using delta C-13 and delta N-15 stable isotope ratios in skin samples. We searched for evidence of geographical and seasonal variation in diet and we explored dietary differences between sexes. Significant differences in the stable isotope ratios of dusky dolphins were found among the 4 gulfs under study. Skin samples from Golfo San Matias and Golfo San Jorge were C-13-enriched and N-15-depleted compared to those from Golfo Nuevo and Golfo San Jose. There was no seasonality in the diet at Golfo Nuevo, and no differences in the diet between sexes in any gulf. Furthermore, Bayesian ellipses of males and females were similar in size and the overlap was mostly symmetrical in Golfo San Jose and Golfo San Jorge, while in the Golfo San Matias and Golfo Nuevo, females had wider ranges of delta N-15, suggesting the exploitation of a wider trophic niche. Finally, pelagic fishes and demersal pelagic squids were identified as the main prey for this species of dolphin, although the proportion of each prey varied regionally.