“Estimativa populacional e distribuição do boto-vermelho (Inia geoffrensis) no reservatório da Usina Hidrelétrica de Balbina, Amazonas, Brasil”

Abstract

The construction of dams in riverine environments has been identified as one of the main factors that can modify the distribution and occurrence of river dolphins. The fragmentation of biological populations in response to the development of hydroelectric dams is a cause for great concern, given the increasing plans for dam construction on the great rivers within the Amazon Basin. Studies of the effect of dams on river dolphin populations of the genus Inia indicate that they can cause fragmentation and isolation, and eliminate population inter-connectivity. The objective of current study was to estimate the size and distribution of a population the endangered dolphin species, Inia geoffrensis (boto-vermelho) which has been isolated for more than 30 years in the reservoir of the Balbina Hydroelectric Power Plant, Amazonian Brazil. To estimate I. geoffrensis density and abundance we used distance sampling methodology, performing 180km (Area = 177km²) of transects along the former courses of the Uatumã and Pitinga rivers. The population was estimated at 1774 individuals (CV = 0.30), with a density of 10 ind./km² (CV = 0.30). To assay botos distributions, we made fixed points surveys in open areas close to the dam, old confluence areas and in an extensive area of dead tree trunks (“paliteiros”) on the left bank of the dam. We found that the species was most common the old bed of the Uatumã river and near the margins of lacustrine islands, where the number of prey is greater. This is the first boto population study at HPP Balbina to use distance sampling methodology. We hope that this will be a starting point for monitoring this population, and that further studies will be conducted to monitor the effects of continuing isolation of dolphins, caused by the Balbina dam, and evaluate the possible impacts for other river dolphin populations of the implementation of new dams on rivers within the Amazon basin.