Population density, abundance estimates, habitat preference and social structure of Amazon River dolphins (<em>Inia geoffrensis</em>) in the Cuyabeno Reserve, Ecuador

Population density, abundance, habitat preference, home range and social structure of Amazon River dolphins or Boto (Inia geoffrensis) were studied in the Cuyabeno Reserve in Ecuador from 1996 to 1998. The study area the Cuyabeno and Lagartococha Rivers are two blackwater tributaries, to the Aguarico River a white ater river. While the Cuyabeno river is flowing through tierra firme forest with numerous oxbow lakes on the 111km stretch surveyed, the Lagartococha river was surveyed on 86,7kms passing through varzea. The maximum population density of 0.39 Botos/km river is fairly low in comparison to other study areas in the lower Amazon basin and depends significantly on season and habitat.Most animals tend to be close to the river mouth during the low water season and in Lagoons with Igap&oacute; and Grasslands during the high water season. Behaviour was most divers in Lagoons with Igap&oacute; and Grasslands, while shallow river sections with beaches are only used as migration passages. Although Botos are considered solitary animals, observations in the Cuyabeno Reserve confirm a high amount of groups from two to eight animals with calves living in groups of three or four animals rather than mother calf pairs. According to Photo ID studies, home range of Botos in the Cuyabeno Reserve extended over different rivers and travelling distances of more than 200kms within the Lagartococha to the Cuyabeno River were recorded. However, most of the dolphins identified according to natural marks on their dorsal fin or back, remained within 50kms, which shows overlapping home ranges of different groups or single animals.