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We assessed the feeding habits of franciscanas (Pontoporia blainvillei) from southern Brazil through carbon and nitrogen stable isotopes measured in the tooth dentin of dolphins from different age classes. Generalized additive models were fitted to test whether sex, age and total body length explained the changes in franciscanas isotope ratios. Bayesian isotope mixing models were applied to estimate the contributions of prey items, selected based on stomach content analysis (SCA), to franciscanas’ diet. Different Trophic Enrichment Factors (TEF) were applied and the results were compared using Bhattachayya's coefficient index to test for differences in models outputs and to define the best TEF for franciscanas. We found different relative importance of the main prey between the methods, and squids' contribution could be lower than suggested by SCA. Since the dentin deposited during nursing seems to influence the isotopic ratios of juveniles, caution is recommended when interpreting dietary estimates based on whole tooth samples . This study is the first characterizing the ontogenetic shifts in franciscanas’ feeding habits using SIA and testing different TEF values. SIA and SCA complement each other in dietary studies, mitigating potential biases resulting from the use of each method separately.
- franciscanas, Pontoporia blainvillei, stable isotopes, feeding habits, mixing models.