Abstract Behavioural Observations of Rough-Toothed Dolphins (Steno Bredanensis) off La Gomera, Canary Islands

(1995-2000) With special reference to their interactions with humans


Fabian Ritter, M.E.E.R. e.V., Berlin, Germany. E-mail: meer@infocanarias.com



Rough-toothed dolphins (Steno bredanensis) were sighted 145 times from 1 September 1995 through 22 March 2000 off La Gomera, Canary Islands. Sightings were made during regular whale watching trips and occurred year-round. Group size ranged from 1 to 50 individuals (mean 16.8, SD=12.0, n=137). Mean depth was 506 m (range 20-2500, SD=473 m, n=140) and mean distance from shore was 4.44 km (range 0.05-14.8, SD=2.33 km, n=137). Behavioural data, collected for 26 sightings showed that the reaction of the animals to the observation vessel varied from no response to interaction. Boat-related behaviours were quantified and were rare up to frequent per sighting, with approaches (46%), bowriding (21%), and scouting (20%) being the predominant types of behaviours. Interactions between the dolphins and swimmers also differed in their duration and intensity. The year-round abundance off La Gomera indicated that this species might endure temperatures well below 25?C. Moreover, for the first time, behavioural categories were defined for the rough-toothed dolphin.

Key words: rough-toothed dolphin, La Gomera, behavioural sampling, boat-related behaviours, interactions with humans