BODY SIZE, DIET, HABITAT USE, AND SOCIAL-BEHAVIOR OF BALAENOPTERA WHALES IN THE GULF OF CALIFORNIA

Four sympatric species of whales in the genus Balaenoptera were studied May 1983-April 1986 in the Canal de Ballenas, Gulf of California, Mexico. Most data were collected on the two most abundant species, Bryde's whale (B. edeni), ca. 13,000 kg and fin whale (B. physalus), ca. 47,000 kg. Bryde's whales fed primarily on schooling fish and were most abundant in summer and autumn when schooling fish are concentrated in the study area. Fin whales were only observed feeding on euphausiids, and were most abundant in winter and spring when euphausiids are abundant throughout the Gulf of California. Bryde's whales fed more at dawn and dusk, whereas fin whales fed throughout the day. Bryde's whales were relatively resident to the study area, rarely traveled in groups, and frequently fed alone or in small aggregations. Fin whales, in contrast, were relatively transient, passing through the study area and lingering only to feed; they traveled in larger groups and fed in larger aggregations, within which there were coordinated groups of two to four individuals. These results, coupled with limited data on the blue whale (B. musculus), ca. 80,000 kg, and minke whale (B. acutorostrata), ca. 5,000 kg, are interpreted in light of theories that relate body size to diet, habitat use, and social behavior in better-studied terrestrial mammals.