Coordinated feeding behavior of the Guiana dolphin, Sotalia guianensis (Cetacea: Delphinidae), in southeastern Brazil: a comparison between populations

ABSTRACT

The coordinated feeding tactics used by delphinids are influenced by differences in the distribution of prey species, season, and opportunities for social learning. In the present study, we compared the coordinated feeding behavior of two populations of the Guiana dolphin, Sotalia guianensis, in southeastern Brazil, and how these feeding tactics vary seasonality and in the presence of calves. We observed eight types of coordinated feeding tactics, which differed in frequency and in the mean number of individuals engaged in them, and between both areas. Feeding tactics used to herd and capture prey were the most frequent and engaged a greater number of individuals, suggesting that these tactics are better for capturing fish that gather in larger schools. Furthermore, the seasons influenced the occurrence of different prey items, which in turn modified the feeding tactics of the dolphins. In the Ilha Grande Bay we observed that bouts lasted longer and larger groups engaged in the feeding tactics, which may be associated with the seasonal spawning of larger schooling fish such as Sardinella brasiliensis (Steindachner, 1879) (Teleostei Clupeidae). However, in the Sepetiba Bay, we observed longer feeding bouts and a smaller number of individuals engaged in the feeding tactics during autumn-winter. This may be associated with the fact that the most abundant prey species, Micropogonias furnieri (Desmarest, 1823) (Teleostei Sciaenidae), gathers in small schools. Calves were present in 95% of all coordinated feeding tactics that occurred in the Ilha Grande Bay and in approximately 61% of feeding tactics in the Sepetiba Bay, suggesting that these areas are important for social learning. This study provides more information about feeding tactics and improves knowledge of the coordinated behavior of Sotalia guianensis (Van Benéden, 1864).