Pinnipeds, seals and sea lions, are an important part of the marine life of southern California. Four species of non-endangered pinnipeds occur in this area: the California sea lion, northern fur seal, northern elephant seal, and harbor seal. Two other species, the Guadalupe fur seal and Steller sea lion, are listed as threatened under the Endangered Species Act.

California sea lions range from British Columbia to Mexico. The world population (excluding a small Galapagos population) is estimated at over 200,000 animals, of which the U.S. population accounts for about 110,000. In California, California sea lions are the most abundant pinnipeds on land and in waters over the continental shelf. They breed in the summer, from May through July, on islands from the Gulf of California in Mexico to the California Channel Islands. In the fall following the breeding season, thousands of California sea lions, mainly immature and adult males, disperse northward from the California breeding grounds to winter along the coast as far north as British Columbia.

California sea lions currently breed on four islands in southern California: San Miguel, San Nicolas, Santa Barbara, and San Clemente. Of these, San Miguel and San Nicolas are by far the largest rookeries. Other islands and nearshore rocks along the coast are frequented by nonbreeding animals. California sea lions feed on a variety of prey, including seasonally abundant small schooling fishes and squids. In southern California, the major components of the California sea lion diet include anchovy, rockfish, whiting, mackerel, squids, and octopus.

Northern fur seals range at sea from the Bering Sea south to Baja California in the eastern North Pacific. The world population is estimated at a little over 1 million animals, of which more than 900,000 are associated with the Pribilof Islands rookeries in Alaska; the remainder are associated with Russian islands and the small San Miguel Island rookery off southern California. This rookery has a breeding population of 5,000 to 7,000 animals. Northern fur seals have been harvested commercially for their pelts since the late 1700's, although currently they are only taken in low numbers in Russian waters

Northern fur seals breed during the summer, from June through August. Pups are weaned in October or November, when their mothers leave the rookeries to begin their winter migration. Following the breeding season, adult females and many juveniles migrate southward along the west coast of North America between Southeast Alaska and California; most adult males apparently remain in Alaskan waters. Fur seal numbers off California, the major wintering ground, peak in February when several hundred thousand are present. Mature females begin returning northward in March, while younger animals may remain until May or June. While at sea, northern fur seals are generally found offshore along the continental slope and shelf. Off California, important northern fur seal prey includes fish species such as anchovy, herring, whiting, saury, rockfish, and a variety of squids.

Northern elephant seals have substantially recovered from near extinction by commercial sealers in the 19th century and have recolonized much of their former range. The species' breeding range presently extends from Baja California to Point Reyes in northern California, and elephant seals range at sea from Mexico to the Gulf of Alaska. As of 1991, the northern elephant seal population was estimated at approximately 130,000 animals.

More than half of the total elephant seal population is associated with rookery islands in southern California. The largest populations are found on San Miguel and San Nicolas Islands; small colonies also exist on Santa Barbara and San Clemente Islands.

Northern elephant seals typically come ashore only to breed and molt. The breeding season lasts from mid-December to March, and pups remain on the rookery for another month or so. Juveniles of both sexes and adult female elephant seals come ashore again to molt their hair and skin in late April and early May. Large males and a few juveniles come ashore for their annual molt in mid-summer, while yearling and some juvenile elephant seals are on land in autumn.

Northern elephant seals make two migrations per year, and the sexes segregate while at sea. Females generally travel to foraging areas in the central Pacific, while males forage in waters in the Gulf of Alaska and south of the Aleutians. Elephant seals are capable of diving to depths of nearly a mile. They apparently forage mainly in waters over and beyond the continental shelf, and feed on a wide variety of prey, including squids, fishes, sharks and rays, lamprey, octopi, crustaceans, and tunicates.

Harbor seals in the eastern North Pacific are found along the coastline from Mexico to the Aleutians. The North Pacific harbor seal population is estimated at 320,000 animals and is centered in Alaska.

In southern California, harbor seals come ashore in greatest numbers on the Channel Islands, particularly the northern chain. Along the mainland, they occur primarily on secluded rocks and beaches. Peak harbor seal populations on land occur during the species' spring breeding and pupping season and during the early summer molt. Following the breeding and pupping season, harbor seals disperse along the coast and spend more time at sea during fall and winter. Although harbor seals apparently do not migrate, movements of 15 miles or more are common. Other studies have documented use of several different beaches sometimes separated by more than 60 miles, by individual seals in a single season. Harbor seals forage close to shore and are typically sighted in coastal waters. They feed on a variety of marine and estuarine prey, including a number of species of fish, lamprey, octopus, squids, and shrimp.