Ecological factors that determine distribution and abundance of the California sea lion Zalophus californianus in the Gulf of California

The population of the California sea lion Zalophus californianus (Lesson, 1828) in the Gulf of California during the breeding seasons of the 1980's was estimated at 23 256 individuals, and 31 393 if census adjustments are applied. Of this total (23 256), 6.9% were adult males, 5.0% subadult males, 40.7% adult females, 23.9% juveniles, 22.7% pups (less than one year of age) and 0.8% were termed miscellaneous. Eighty-six percent of the 29 sea-lion colonies studied were on islands, while the remaining colonies occupied capes of the mainland. However, around 98.8% of the sea-lion population was counted on islands. The sea-lion distribution in the gulf was determined by the concentration of its usual preys (sardine, anchovy, mackerel and hake). The operational sex ratio varied according to island size in a negative exponential trend. -from Authors