Trophic Relationships and Habitat Preferences of Delphinids from the Southeastern Brazilian Coast Determined by Carbon and Nitrogen Stable Isotope Composition

To investigate the foraging habitats of delphinids in southeastern Brazil, we analyzed stable carbon (delta C-13) and nitrogen (delta N-15) isotopes in muscle samples of the following 10 delphinid species: Sotalia guianensis, Stenella frontalis, Tursiops truncatus, Steno bredanensis, Pseudorca crassidens, Delphinus sp., Lagenodelphis hosei, Stenella attenuata, Stenella longirostris and Grampus griseus. We also compared the delta C-13 and delta N-15 values among four populations of S. guianensis. Variation in carbon isotope results from coast to ocean indicated that there was a significant decrease in delta C-13 values from estuarine dolphins to oceanic species. S. guianensis from Guanabara Bay had the highest mean delta C-13 value, while oceanic species showed significantly lower delta C-13 values. The highest delta N-15 values were observed for P. crassidens and T. truncatus, suggesting that these species occupy the highest trophic position among the delphinids studied here. The oceanic species S. attenuata, G. griseus and L. hosei had the lowest delta N-15 values. Stable isotope analysis showed that the three populations of S. guianensis in coastal bays had different delta C-13 values, but similar delta N-15 results. Guiana dolphins from Sepetiba and Ilha Grande bays had different foraging habitat, with specimens from Ilha Grande showing more negative delta C-13 values. This study provides further information on the feeding ecology of delphinids occurring in southeastern Brazil, with evidence of distinctive foraging habitats and the occupation of different ecological niches by these species in the study area.