Bolivian river dolphin site preference in the middle-section of Mamoré River, upper Madeira river basin, Bolivia

Abstract

The South American river dolphins of genus Inia are distributed throughout the Amazon, Orinoco and Araguaia-Tocantins basins. They are categorized as Endangered and the knowledge on their basic ecology is still scarce. Therefore, investigation efforts must contribute to the knowledge and conservation of these species in their area of distribution. For the Bolivian river dolphin we used a database of 10 years of upstream and downstream surveys, accumulating approximately 6,100 km of double routes from three main rivers of the Upper Madeira River basin (Ibare, Mamoré and Tijamuchi) by following standardized methods where each encounter with a single or a group of river dolphins was registered. Preferred sites by Bolivian river dolphin were based on Kernel density estimation. This methodology considers the accumulated data of georeferenced sightings, generating a map of probability of occurrence in each river. In the three rivers, the accumulated density of sightings is concentrated in meanders and confluences, resulting in a high probability of sighting Bolivian river dolphin in these habitats. It was also identified that the number of Bolivian river dolphin sightings decreased over time in the upper Tijamuchi River. The Bolivian river dolphin preferred both meanders and confluence habitats. Between the Ibare and Tijamuchi rivers (Mamoré sub- basin), the distribution of the species tended to be more uniform. According to these results, it is important to reinforce the management of the Ibare-Mamoré municipal protected area, since important Bolivian river dolphin populations are concentrated there. Same trend was also shown in the lower-middle zone of the Tijamuchi River, suggesting the need of implementing conservation strategies in this area, where currently there are none.