Reproduction

Between May and August the sea lions gather at a rookery where they will breed.

Here males establish a territory which they defend for as long as possible. They do not eat during this period living off the blubber. A larger male will be more successful as he can store more blubber. It is very hot during the breeding season so part of the territory always has water for the male to sit in with some even being completely in the water.

Females form a group of 2-20 individuals and begin to move through the territories of the males. Males do not work too hard to keep females in their territory and females do not like males to be too energetic or aggressive.

There is a delay between mating and implantation of three months. Following this gestation takes 8 months. They give birth in June or July. A single pup is born at the end of this period.

For the first week of their life the mother stays with the pup to nurse it. After this she heads out to sea for up to three days before returning to spend 2-3 days nursing the pup. While they are left on the shore pups form nurseries where they can socialize and play. The mother and pup can find each other on the beach due to their distinct calls.

Weaning age varies greatly in California sea lions. Some wean at 6 months while for others it takes a year. There is believed to be a number of reasons for this. These include food availability, the mother’s age, the sex of the pup and if a new pup is born. Females spend more time with the mother before striking out on their own than males do.

Sexual maturity occurs between 4 and 5 years of age though most males cannot hold a territory until they are much older.

Some instances of pups being fostered by other sea lions after they are abandoned have been recorded.

Behavior

California sea lions are highly social. They gather in large groups to rest and will tolerate others lying on them or close to them. In the water they create a raft which is a mass of sea lions close together. When it is time to go hunting they form small groups unless they are going after a large number of fish.

When diving they can reach depths of 274m (899ft) and swim at between 15-20mph (24-32 km/h).

Juvenile and non-breeding California sea lions have been seen engaging in play activities such as surfing, chasing each other, pushing and shoving each other off rocks and mock fights. On occasion adults are seen participating.

The California sea lion is one of the most vocal mammals. They make barks, growls and grunts.

Predators and Threats

Natural predators of the California sea lions include orcas, coyotes, wild dogs and great white sharks. Bald eagles used to take pups but have now gone extinct in the range of this species.

Humans affect the population of California sea lions through entanglement in fishing gear, toxins from algal blooms and injuries caused by humans such as gunshots.

Populations of this species have increased since 1975 when they were offered protection under the Marine Mammal Protection Act.

Quick facts

California sea lions are the ones most commonly seen performing at zoos and aquariums. They are highly intelligent and have been taught to understand a simple version of sign language.

Groups of California sea lions have been trained for use in military operations and are still part of active duty today.