Group Size, Habitat Use and Behavioral Ecology of Amazon River Dolphins (Inia geoffrensis and Sotalia fluviatilis) in the Pacaya-Samiria National Reserve, Peru

Abstract

Two species of cetacean occur sympatrically in the Amazon River and its tributaries; botos (Inia geoffrensis) and tucuxis (Sotalia fluviatilis). Little information exists on the ecology of each species as well as any differences in their ecology. In this study, a generalized linear model was used to examine the habitat use and behavior of botos and tucuxis along a small river system in the Pacaya-Samiria National Reserve, Peru. Analysis of habitat use indicated that botos used confluences significantly more than any other river habitat and tucuxis used river centers significantly more than any other habitat along the Samiria River. Tucuxis used the river center significantly more than any other habitat type, followed by confluence and river-center habitat, whereas botos used the confluence significantly more than any other habitat type and showed now significant distinction between the other habitat types (except river center, which was least used). The differences in habitat use between the two study species may be indicative of how they avoid competing with each other and may be indicative of niche separation between the two species. Group size data was collected for both species during July and August 2011 and compared with group size data from published data from other regions and was also used to highlight differences between the respective biology of each species. Group size differed significantly between species, with tucuxis being observed in larger groups than botos, which may indicate tucuxis are more social than botos. Additionally, observed behavior differed between the two species, with tucuxis socializing significantly more than botos. These results may indicate that socializing is a more integral component in the biology of tucuxis than that of botos. The differences in sociobiology between each species will help provide information on the life history of each species in small rivers, which is not well documented. Furthermore, by examining the ecology of botos and tucuxis, inferences can be made about each species’ ecological requirements of each species in small rivers, which can be used to help create more effective conservation strategies that adequately protect the needs of both species.