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ANIMAL ESTATE client 5.4: California Sea-Lion


SCIENTIFIC NAME: Zalophus californianus

ANIMAL PROFILE: The California sea lion belongs to the family Otariidae which means "little ears". There are two geographically separate subspecies of California sea lion recognized: Zalophus californianus californianus, which is found off the west coast of North America, and Zalophus californianus wollebaeki, which lives in the Galapagos Islands in the Central Pacific Ocean. A third subspecies, Zalophus californianus japonicus once lived near Japan but is now thought to be extinct.

The California sea lion is the fastest aquatic carnivore, it can swim up to 25 mph   when pressed, often "porpoising" along at the surface. It can descend to 450 feet (137 m) and stay submerged for 20 minutes, using sonar for underwater navigation and finding prey. Spending much of the day sleeping on islands, the California Sea Lion hunts primarily at night, feeding at depths of 85 to 240 feet (26-74 m) on squid, octopus, abalone, and more than 50 species of fish, usually Pacific whiting, juvenile rockfish, Pacific and jack mackerel, and market squid, which it eats by snapping off the head and swallowing the remainder.

The bull is among the most vocal of all mammals, continually giving a honking bark while defending his territories. The cow makes a quavering wail to summon her pup, and barks and growls in aggressive interaction with other cows. The pup recognizes its mother's voice and responds with a lamb-like bleat. The sexes remain segregated outside the breeding season, males traveling north in August or September as far as British Columbia while females and young remain in the waters off rookeries. The breeding male establishes a territory in May, June, or July in southern California and defends it against neighboring males. The males lunge at one another, each trying to bite his adversary's front flippers. During the breeding season, the fasting bull maintains a territory but does not attempt to keep a specific harem. Females arrive and segregate into harems of 3-40 individuals, depending on the size and strength of the male. The female hauls out in May or June and gives birth about four to five days later to a pup conceived the spring before. The mother nurses the pup for about eight days, then begins foraging trips, which at first last two days, then three to four days. Between trips, the mother returns for 30 to 70 hours to nurse. This pattern continues until weaning, which in California rookeries (colonies of breeding animals) takes place at four to eight months.

Although a pup may nurse for eight months, it also eats fish. While   learning to swim, it often rests on its mother's back. California Sea Lions mate three to four weeks after the females have given birth. They usually mate in the water or at water's edge as the female returns or departs on a foraging trip. A period of delayed implantation insures that the young will be born in a year, when the breeding herds again form. The female breeds at four years, but the male must wait several more years before he is big enough to compete for territories. To tell mature California sea lion males from females, look for the bump or "crest" the males develop on their heads around five years of age. As males get older the fur on the crest and around their whiskers gets lighter. Sea lions exhibit sexual-dimorphism, adult male California sea lions can reach 1,000 pounds in weight and 7 feet in length. Adult females can grow to 350 pounds and 6 feet in length.

Social organization during the non-breeding is unstable. However, a size-related dominance hierarchy does exist. Large males use vocalization and movement to show their dominance and smaller males always yield to them. Non-breeding groups are gregarious on land and often squeeze together. Most sea lions found in man-made environments are males or juveniles, because sea lions don't breed there and it is mostly those groups that migrate to those places during the non-breeding season.

RANGE: California sea lions are found along the shore from California to Mexico including Baja and Tres Marias Islands, in the Galapagos Islands.

HABITAT: The sea lion's habitat is mostly water. It also can live on land for a long period of time. California sea lions are very social and form groups of several hundred when they are onshore. On land it must be on a shoreline where it is rocky. The California sea lion generally live along coastlines but have been found in rivers along the northern Pacific coast. The climate must be warm. These animals do not have to migrate so far south because they are in California. They migrate south to the tip of South America where it is warmer when the temperature cools down.

HOME CONSTRUCTION: California sea lions often congregate on man-made structures such as jetties, piers, offshore buoys and oil platforms. They tend to inhabit places which have undergone human intervention.

THREATS: Killer whales and great white, hammerhead, and blue sharks occasionally prey on the California Sea Lion. It was once killed for the oil rendered from its blubber, and also for its meat, which was used for dog food. More recently, a significant number of California sea lions have been killed as a result of getting tangled in discarded fishing gear. From 1983 to 1984, Z. californianus experienced a decline of 60 percent in pup production from previous years. Also during this time food resources declined, which led to inhibited growth and increased mortality. Mothers left their pups earlier in search of food, which truncated the lactation period, thus reducing the amount of nutrients a pup received and making it more susceptible to death.

INTERESTING FACTS: The stomach of an average California sea lion may contain as many as 100 pieces of gravel sized rocks. No one is sure yet what they are used for but it is believed that they are used to ease hunger pains during their mating and fasting periods. / In the scientific community, there are many debates concerning the ancestry of eared seals. It is believed that eared seals and walrus' descended from a bear-like ancestor that returned to the sea 30 million years ago in the North Pacific. / California sea lions are very social animals, and groups often rest closely packed together at favored haul-out sites on land, or float together on the ocean's surface in "rafts."


Sea lions have a long history of taking refuge and holding court on boat docks, as well as buoys. A prime example of sea lions desire to rest on landings is occurring at Pier39 in San Francisco.

A few Sea Lion Cam Sites:

Pier 39

The Race Rocks Taxonomy: A camera provided by Lester B. Pearson College


Animal Diversity Website

National Marine Sanctuaries



NOAA Fisheries Office of Protected Resources



The Marine Mammal Center



by Ann Bauer, The Marine Mammal Center, for the Animal Estates 4.0 Field Guide

California sea lions are known for their intelligence, playfulness, and noisy barking.   They are a member of the group called "pinnipeds" or flipper-footed animals including fur seals, seals and walruses. They are distinguished from seals by their external ear flaps and large flippers that they use to "walk" on land.   The trained "seals" in zoos and aquariums are usually California sea lions. Their color ranges from chocolate brown in males to a lighter, golden brown in females. Males reach up to 850 lbs. (390 kg) and seven feet (2.1 m) in length. Females grow to 220 lbs. (110 kg) and up to six feet (1.8 m) in length. Adult males have a thick neck and at about five years of age, males develop a bony bump on top of their skull called a sagittal crest.   They range along the Pacific Coast from Vancouver Island, British Columbia, to the southern tip of Baja, Mexico.

Although their fur was not coveted like sea otters and fur seals, they were hunted occasionally by indigenous people and settlers for meat. At the turn of the century there was a bounty on sea lions as they were considered competitors to the fishing industry.   Since 1972, they have been protected under the Marine Mammal Protection Act and their population has grown steadily.   As populations increased, sea lions return to areas they historically inhabited.   California sea lions have not only returned to rocky shores and sandy beaches on the mainland and offshore islands, but they are appearing in areas with a lot of human activity.   In fact, humans have produced a new "habitat" where sea lions can "haul out" on docks, jetties, buoys and derelict boats.

California sea lions are very social animals, and groups often rest closely packed together at favored haul-out sites on land, or float together on the ocean's surface in "rafts." They are sometimes seen "porpoising", or jumping out of the water, presumably to go faster. Sea lions have also been seen "surfing" breaking waves. California sea lions are opportunistic eaters feeding on whatever prey fish is available including squid, octopus, herring, rockfish, mackerel, salmon, lamprey and small sharks.   In turn, sea lions are preyed upon by orcas (killer whales) and great white sharks.

Sandy beaches of offshore islands from southern California's Channel Islands south to Mexico are their chosen rookery sites where pups are born.   Single pups are born in June or July and weigh 13-20 lbs. (6-9 kg). On average, they nurse for at least five to six months, but some may nurse for over a year. Mothers recognize pups on crowded rookeries through smell and vocalizations. Pups also learn to recognize the vocalizations of their mothers. Males patrol specific territories barking and engaging other males in pushing and biting fights during the breeding season to hold there territory.   Males mate with females in their territories a few weeks after females give birth.   Males leave the rookeries and move north after the breeding season in July.

Sea lions swim into the San Francisco Bay to escape predators and sleep at the surface of calmer Bay waters or on land.   In the winter, they come to feed on herring that spawn in the Bay.   In September 1989, sea lions began to appear consistently at PIER 39's K dock.   The dock had recently been refurbished and for a period of time no boats were docked, leaving large open spaces where sea lions could easily haul out.   When the boats returned, no real effort was made to discourage the few sea lions from hauling out.     Historically, California sea lions had been observed on Seal Rock, an island north of Ocean Beach, below the Cliff House Restaurant in San Francisco.   As the number of sea lions at PIER 39 increased, the number at Seal Rock decreased.   What made them change their preferred haul out is unknown.   The winter herring run brought 150 sea lions to PIER 39 and by March the population was more than 400.   In May of this year, 765 sea lions were counted.

It is certain that K dock provides a safer habitat for sea lions then Seal Rock as sea lions' predators (great white sharks and orcas) do not enter the Bay.   The docks are easy for sea lions to jump onto, as they float with the tides.   Sea lions resting on rocks must climb up and move as the tide rises, or abandon their spot altogether if it becomes submerged so floating docks must be more appealing to sea lions.

In 1989 PIER 39 contacted The Marine Mammal Center for advice and information. The Center recommended the use of herding boards (like shields) for people walking on the docks, and indicated that moving the boat owners from K dock would be the safest precaution.   PIER 39 relocated the boats from K dock to other locations in their Marina and the dock was officially closed to the public and set aside for the sea lions. Since then, PIER 39 has worked with The Marine Mammal Center to ensure the safety of visitors, boat owners and sea lions. The Marine Mammal Center has rescued more then 50 sick and injured sea lions from the PIER 39 Marina.   The Center also conducts education programs for school groups and provides information to tourists.

It is illegal in the U.S. to feed, harm or harass all marine mammals.   PIER 39 is allowed to keep its marina safe for boats and the public.   They are allowed to make repairs to the docks, including K dock and dredge the marina.   In the absence of tidal action to clear away sea lion fecal matter, K dock is hosed off once a week April - October.   A boat pulling a small raft with a compressor pumps bay water that is sprayed on the docks to clean them.   The continued presence of the California sea lions at PIER 39's K dock is an excellent example of humans and wildlife coexisting. In a world where increasing pressure on scarce resources such as waterfront property and fish more often pit us against wildlife, humans and sea lions at PIER 39 have come to a mutual arrangement that works for both.