MARINE MAMMAL SCIENCE, **(*): ***–*** (*** 2011) C ! 2011 by the Society for Marine Mammalogy DOI: 10.1111/j.1748-7692.2011.00468.x Population, density estimates, and conservation of river dolphins (Inia and Sotalia) in the Amazon and Orinoco river basins CATALINA GOMEZ-SALAZAR Biology Department, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada and Foundation Omacha, Calle 86A No. 23-38, Bogota, Colombia E-mail:
[email protected] FERNANDO TRUJILLO Foundation Omacha, Calle 86A No. 23-38, Bogota, Colombia MARCELA PORTOCARRERO-AYA Foundation Omacha, Calle 86A No. 23-38, Bogota, Colombia and Hull International Fisheries Institute, The University of Hull, Hull, HU6 7RX, United Kingdom HAL WHITEHEAD Biology Department, Dalhousie University, Halifax, Nova Scotia B3H4J1, Canada ABSTRACT This study is part of an on-going effort to evaluate and monitor river dolphin populations in South America. It comprises the largest initiative to estimate pop- ulation size and densities of Inia and Sotalia dolphins using statistically robust and standardized methods. From May 2006 to August 2007, seven visual surveys were conducted in selected large rivers of Bolivia, Colombia, Brazil, Ecuador, Peru, and Venezuela in the Amazon and Orinoco river basins. Population sizes of Inia and Sotalia were estimated for different habitats (main river, tributary, lake, is- land, confluence, and channel). A total of 291 line and 890 strip transects were conducted, covering a distance of 2,704 linear kilometers. We observed 778 Inia geoffrensis,1,323Inia boliviensis,and764Sotalia fluviatilis.High-densityareaswere identified (within 200 m from the river banks, confluences, and lakes) and we pro- pose that these constitute critical habitat for river dolphins.