Abstract: Studies of the biology and ecology of Commerson’s dolphins (Cephalorhynchus commersonii) in the Ría Deseado estuary (47º 46′ S, 65º 58′ W) were carried out during January-February 1986 to 1991 and 1994 to 1997, August 1987 and 1988, September 1995, and May 2003. Commerson’s dolphins were consistently located along a 24-km stretch of the Ría Deseado. Twenty-six dolphins were identified using marks, scars, and differences in the black and white pigmentation of the head, back, and sides. Two adult dolphins with the typical grey colour pattern of the calves of this species have been observed since 1994. Behavioural observations were recorded and fell into four general categories: (1) traveling (51%), (2) resting (21%), (3) feeding (19%), or (4) socialising (9%). Feeding behaviours included dolphins feeding at the surface, near anchor lines, and around piers. Commerson’s dolphins were directly observed feeding on silversides (Odontesthes). Calves were observed between mid-September and mid-March, which suggests that calves are born in the austral spring and early summer. Interactions between dolphins and seabirds/marine mammals were recorded. Killer whales (Orcinus orca) may prey on Commerson’s dolphins in this area.

Key Words: RÍA DESEADO; COMMERSON’S DOLPHIN; CEPHALORHYNCHUS COMMERSONII; ANOMALOUS COLOUR PATTERN; BEHAVIOUR; INTERACTIONS WITH OTHER SPECIES

Document Type: Research article

DOI: 10.1578/AM.33.3.2007.276

Page Numbers: 276 – 285