Distribution and abundance of the Amazon river dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) in the Upper Amazon river Academic Article uri icon


  • A boat survey was conducted from 5 to 26 June 1993 to estimate the abundance of the Amazon river dolphin (Inia geoffrensis) and the tucuxi (Sotalia fluviatilis) along ca. 120 km of the Amazon River bordering Colombia, Peru, and Brazil. Two survey methods were used: line transects during 5 d and strip transect during 15 d. The line transect were used to estimate the abundance of both species in the main channels of the Amazon at distances greater than 200 m from river banks and islands, and strip transects were used to estimate abundance in the remainder of the habitat. A total of 29 sightings was obtained using line transects, including 8 Inia. 15 of Sotalia, and 6 with both species present. The total number of sightings made while using strip transects was 143, including 78 of lnia, 51 of Sotalia, and 14 with both species present. The distributions of sightings with respect to distance from the nearest bank were not significantly different between the two species. Based on the results from the two methods, we estimate that there are 346 (CV = 0.12) lnia and 409 (CV = 0.13) Sotalia in the study area. Overall, the mean group size for Inia was 2.9 individuals and for Sotalia was 3.9 individuals. lnia density (dolphin/km2) was highest in tributaries (4.8), followed by areas around islands (2.7) and along main banks (2.0); while Sotalia density was highest in lakes (8.6), followed by areas along main banks (2.8) and around islands (2.0). These are among the highest densities measured to date for any cetacean.

published proceedings


altmetric score

  • 7

author list (cited authors)

  • Vidal, O., Barlow, J., Hurtado, L. A., Torre, J., Cendon, P., & Ojeda, Z.

citation count

  • 42

complete list of authors

  • Vidal, O||Barlow, J||Hurtado, LA||Torre, J||Cendon, P||Ojeda, Z

publication date

  • July 1997