On land, occur in small groups and dense rookeries during breeding and non-breeding seasons. Females give birth and nurse on land, entering water alone, or with pup, for thermoregulatory purposes, and alone during feeding trips. Prefer haul-out and breeding sites with nearby food supply, and easy access to water where human disturbance is minimal. Large groups may be frightened into the water by the appearance of a person. Yearlong, circadian activity pattern.
Adult males maintain terrestrial and aquatic territories in breeding season.
Breed May to August. Highly polygynous, adult males establish and defend territories. Preferred territories contain highest number of females, and controlled by largest breeding bulls. Males maintain territories for 2-6 wk. Females give birth to a pup 1-2 days after arrival, come into estrus and mate about 2 wk following parturition.