Occurrence Patterns and Trends of Cetaceans Recorded from Southeast Farallon Island, California, 1973 to 1994

Abstract

We summarize 22,682 observations of 15 species of cetaceans from Southeast Farallon Island off San Francisco, California, 1973 to 1994. Gray whales (Eschrichtius robustus) accounted for 63% of the observations. Most of these were of migrant individuals in the winter and spring, but up to 10 summer/fall residents were also recorded around the island each year. The other 14 species were recorded primarily from July to November. Observations of all cetaceans and of several different species increased significantly during the 22-yr period. These increases may be related to population recoveries due to protection of the large whale species, possible increases or changes in food resources in the Gulf of the Farallones region, possible observer biases, or likely, a combination of these factors. The occurrence of Pacific sardine (Sardinops sagax) in the region during the last three years of the study may have resulted in changes in the distributions of several species.