Abundance estimation of Commerson's dolphin in the eastern area of the Strait of Magallan-Chile

Abundance of Commerson's dolphin, Cephalorhynchus commersonii (Lacepede 180 4), in the eastern portion of the Strait of Magellan was estimated by means of aerial transects in autumn (June 1996). Using a helicopter at 100m alti tude and 129 km h(-1), 58 sightings representing 98 animals (average group size Es = 1.7, SD = 0.13) along 818.6 km of linear transects were recorded. Data analysis with "Distance" software gave a density estimation of 0.34 i nd km(-2) (CV = 0.27) and a population size of 1,206 (95% CI 711-2,049 indi viduals). Commerson's dolphin showed a habitat preference for the narrows, compared to open waters in the study area.