Zalophus californianus
California sea lion

Zalophus californianus are found along the shore from California to Mexico including Baja and Tres Marias Islands, in the Galapagos Islands and in the southern Sea of Japan (Scheffer, 1958). The populations in each area do not interact with other populations (Scheffer, 1958) and therefore are considered subspecies. California sea lions tend to seasonally migrate long distances (Riedman, 1990). Males usually migrate north to British Columbia after the breeding season (Mate, 1978).

Zalophus californianus generally live along coastlines but have been found in rivers in along the northern Pacific coast. California sea lions often congregate on man-made structures such as jetties, piers, offshore buoys and oil platforms. Zalophus californianus tend to inhabit places which have undergone human intervention (Riedman, 1990).

Newborn pups average 75 cm in length and weigh between 5 to 6 kg. Adult males average 2.2 meters in length and 275 kg in weight but can reach length of 2.4 meters and weights of 390kg. Females are smaller, averaging 1.8 meters in length and 91 kg in weight but can reach lengths of 2 meters and weights of 110kg . Pups have a blackish brown coat, which is molted by the first month and replaced with a light brown coat. The light brown coat is shed after 4 or 5 months and replaced with the adult pelage. Adult males are mostly dark brown with lighter belly and side coloring. Adult females are dark brown but can also appear tan. Zalophus californianus exhibit pronounced sexual dimorphism . Adult males have an enlarged saggital crest and a lighter pelage. In addition to the head features males are more robust and larger than females. All California sea lions have black flippers which are coated with short black stubble. The typical dental formula is 3/2, 1/1, and 5/5.

(Mate, 1979,)(Jefferson et al., 1993), and (Riedman, 1990)

The oldest recorded wild Z. californianus lived 17 years (Mate, 1979).

In captivity, the oldest recorded Z. californianus lived to be 31 years old. The age of Z. californianus can be determined by counting the number of rings on cross sections of its teeth (Mate, 1978).

Zalophus californianus are capable of diving to depths of 274 meters (Riedman, 1990) and can reach speeds of 15 to 20 miles per hour while swimming (Mate, 1978). Like certain other marine mammals, Z. californianus use a system of echolocation to find food, orient themselves, and navigate underwater. Z. californianus sometimes adopt and foster a pup that has been abandoned by its mother (Riedman, 1990).

The normal body temperature of Zalophus californianus is 37.5 degrees Celsius. Because Z. californianus cannot sweat or pant (Odell, 1981), in order to thermoregulate they must alter their exterior environment. For example, if the air temperature increases they seek cooler areas, such as water (Riedman, 1990).

Pups exhibit many different play behaviors including mock fighting (Mate, 1978).

Male California sea lions have been known to assemble at the mouths of fresh water rivers where there is a steady supply of fish. California sea lions tend to feed alone or in small groups unless there is an large quantity of food. Under conditions of increased food supply, Z. californianus hunt in larger groups. Zalophus californianus have been known to feed cooperatively with cetaceans, seabirds and harbor porpoises. Often one species locates a school of fish and signals the presence of food to the other species. While rare, it has been recorded that California sea lions drink seawater while not breeding (Riedman, 1990).

Foods eaten include: cephalopods, anchovies, herring, Pacific whiting, rockfish, hake, salmon, squid and octopuses (Riedman, 1990).

See Riedman, 1990.

California sea lions are thought by some to seriously reduce stocks of commercially-valuable fish such as salmon. They also may interfere with nets used by fishermen.

Zalophus californianus used to be hunted for their hides and for animal food. California sea lions are also used by the U.S. Navy for retrieval programs, including search and rescue and retrieval of military hardware. They are also used to patrol areas in search of threats. California sea lions are widely used in educational programs throughout the world because of their agility and trainability. They are charming ambassadors for their sea lion cousins. (Mate, 1978; Mate, 1979)

Zalophus californianus are well protected in most areas. Occasionally, they are trapped with a permit for display in zoos, aquariums, and circuses (Mate, 1979). In Mexico, a few California sea lions are trapped each year, while in the United States they are fully protected under the Marine Mammal Protection Act.

Occasionally California sea lions pose a problem for fishermen by stealing fish from commercial fishermen netting. A significant number of California sea lions have been killed as a result of getting tangled in discarded fishing gear. (Riedman, 1990). 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. During this time 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.

According to IUCN, the following subspecies are recognized:

Zalophus californianus ssp. japonicus (extinct)

Zalophus californianus ssp. wollebaeki (vulnerable)

Zalophus californianus ssp. californianus (no special status).

Because Z. californianus are highly trainable (Riedman, 1990), they are often used as performing animals in zoos, circuses and aquariums (Jefferson et al., 1993).

In 1970, a disease called leptospirosis spread throughout the California sea lion population via urine. This disease was the first documented widespread disease in marine mammals. The origin of the leptospirosis was believed to be Mexico due to the warmer water there, which was conducive to bacteria growth. (Mate, 1978)