The dammed river dolphins of Brazil: impacts and conservation

A major threat to river dolphins in Brazil is habitat loss and fragmentation as a result of the construction of hydroelectric dams. We examine the degree of overlap between the distributions of two river dolphin species (boto Inia geoffrensis and tucuxi Sotalia fluviatilis) and hydroelectric projects and provide an initial quantification of impacts. The locations of dams were overlaid onto a map of the known distributions of the dolphins. Two types of impacts were evaluated: population fragmentation and effects on prey. For each of these a binary score (for absence or presence) was assigned for each dam. The sum of all impact scores for each dam, in each of the three watersheds in which dolphins are found, including realized and potential impacts, was calculated as the impact index. Thirteen dams affect the distribution of I. geoffrensis (as could a further three dams under construction and seven planned), and three dams affect S. fluviatilis (as could three under construction and two planned). Overall, the impact index was higher for I. geoffrensis than for S. fluviatilis. The Araguaia-Tocantins and North Atlantic watersheds have higher impact index values than the Amazon watershed. Although some impacts of damming could not be considered in this study, our approach was a rapid initial risk assessment that provided an overall understanding of how river dolphins are and may be affected by hydroelectric projects in Brazil. Our method may be applicable to other freshwater cetaceans and species facing similar threats when information about impacts is incomplete.