Environmental Variables Affecting the Residence of Spinner Dolphins (<I>Stenella longirostris</I>) in a Bay of Tahiti (French Polynesia)

Abstract

The spinner dolphin (Stenella longirostris) is the most common among 16 species in the Society Islands (French Polynesia). They are observed yearround during daytime in sheltered bays or within lagoons. From 1995 to 2002, we studied spinner dolphins from a shore site in Baie des Pecheurs, a bay on the west coast of Tahiti, performing 1,033 sighting sessions with binoculars. Presence, position, and school size were noted, as well as various behavioral and environmental variables. Human presence also was recorded. Dolphins were present on average 73.3% of the days, with a higher presence rate from May to November (81.0%) than from December to April (66.7%). Dolphins stayed within the bay from early morning until 1200 to 1500 h and had school sizes ranging from as small as 15 to 30 to as large as 100 to 140 individuals. Dolphins began to move slowly offshore after 1100 h. On average, they stayed 400 m from shore, although they approached as close as 100 to 150 m. Dolphin presence and residence time seemed to be negatively affected by surface water turbidity (river flow) and lagoon current strength. Recreational dolphin watching was low from Monday to Thursday (0.20 to 0.35 boat per sighting session) and high on Sunday, with an average of 1.67 boats per session. There was a lower dolphin presence rate from Monday to Thursday (69%) than from Friday to Sunday (78%). Presence patterns were similar to those found in Hawaii, accounting for differences in environmental characteristics.