Effect of boat traffic on the vocal and surfacing behavior of river dolphins: A key for abundance estimation methods Free

To evaluate the effect of boat traffic on vocal and surfacing behavior of river dolphins, Inia geoffrensis and Sotalia fluviatilis, field recordings and scanners were carried out in the Amazon River during 2001. Changes on surface dolphin activities and vocalization rates were analyzed. Twenty complete slot interferences between boats and dolphin vocal behavior were selected from 2400 min of total recording. Significant differences between signal types (squeals for Inia and whistles for Sotalia) between pre‐exposure, exposure, and post‐exposure to the interference were found, for both Inia and Sotalia species. Six hundred scanners were conducted from a 6‐m‐high base observation platform. Interferences with pre‐exposure, exposure, and post‐exposure times were selected with only one boat crossing the dolphin area. Significant differences in frequency, type of event, and immediate response were observed for both Inia and Sotalia species, especially when a speedboat was crossing the area at high speed. This information shows that boat traffic did affect vocal and surface behavior of river dolphin species inhabiting the Amazon River in Colombia, and that abundance estimations using boat transect along the river may change depending upon the type and speed of the vessel used.