Occurrence and Habitat Use of Marine Mammals at Santa Catalina Island, California from 1983-91

A nine-winter-long study (1983-91) of marine mammals at Santa Cat- alina Island, California provided data on the ecological relationships among three pinniped and nine cetacean species observed there. A dramatic reduction in the number of California sea lions occurred during and following the winter with the most severe effects from the 1983 El Nino. The most striking change in cetacean occurrence was a precipitous decline in pilot whale numbers followed by an increase in abundance of Risso's dolphins. The six most often-sighted cetaceans appeared to partition the habitat according to water depth and distance from shore.