Abstract

A total of 1,715 km of boat-based surveys and 1,521 km of aircraft-based surveys was conducted from 1986–1989 to assess the distribution, relative abundance, and ecological relationships of cetaceans in the northern Gulf of California. Seven cetacean species were seen; in decreasing frequency of groups encountered they were: bottlenose dolphins, Tursiops truncatus; vaquitas, Phocoena sinus; common dolphins, Delphinus delphis; fin whales, Balaenoptera physalus; Bryde’s whales, B. edeni; gray whales, Eschrichtius robustus, and killer whales, Orcinus orca. Common dolphins were numerically dominant and bottlenose dolphins were seen most often. Bryde’s whales and vaquitas had the smallest group sizes. In general, the odontocete cetaceans were separated spatially, whereas the distribution of Bryde’s and fin whales overlapped considerably.