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Zalophus californianusCalifornia sea lion

By Rebecca Price

Geographic Range

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).

Habitat

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).

  • Aquatic Biomes
  • rivers and streams
  • coastal

Physical Description

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)

  • Range mass
    390 (high) kg
    859.03 (high) lb
  • Range length
    2.4 (high) m
    7.87 (high) ft

Reproduction

During breeding season males claim territories. A male consistently occupies a territory until factors change and cause him to be displaced. Typical occupation time is approximately two weeks; few Z. californianus males remain at their site for longer. While guarding their territory, males remain present and do not leave even in pursuit of food. As external factors change, males replace other males on the territory. Replacement occurs throughout the entire breeding season. Males are known to attack if others invade their territory. California sea lions tend to breed on islands or remote beaches. Zalophus californianus exhibit moderate to extreme polygyny and tend to live in colonies of a few males and many females. Female Z. californianus exhibit mate choice, by "respond[ing] differently to the attempts of various males"(Riedman, 1990).

The peak breeding season occurs in early July. The total gestation period is about 11 months (Riedman, 1990). Most births occur from mid-May to mid-June (Scheffer, 1958) with the majority of pups born in mid-June. The time between birth and estrus is about 28 days. California sea lions reach sexual maturity between four and five years (Riedman, 1990).

  • Breeding season
    mating in July, births in mid-May to mid-June
  • Average number of offspring
    1
  • Average number of offspring
    1.2
    AnAge
  • Average gestation period
    11 months
  • Average gestation period
    259 days
    AnAge
  • Range weaning age
    6 to 12 months
  • Average age at sexual or reproductive maturity (female)
    4-5 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    1095 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    4-5 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    1826 days
    AnAge

The lactation period in Z. californianus ranges from six months to a year. There are many possible reasons for the variation in lactation periods including availability of food resources, the mother's age and health, the sex of the pup and the birth of a new pup. Zalophus californianus provide more lengthy maternal care for female offspring then for male offspring, yet during lactation both males and females have equal access and receive equal resources.

Lifespan/Longevity

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).

Behavior

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).

Communication and Perception

Food Habits

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).

  • Animal Foods
  • fish
  • mollusks

Predation

See Riedman, 1990.

Economic Importance for Humans: Positive

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)

  • Positive Impacts
  • ecotourism
  • research and education

Economic Importance for Humans: Negative

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.

  • Negative Impacts
  • crop pest

Conservation Status

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).

Other Comments

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)

Contributors

Rebecca Price (author), University of Michigan-Ann Arbor, Kate Teeter (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

internal fertilization

fertilization takes place within the female's body

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

References

Jefferson, T., S. Leatherwood, M. Webber. 1993. Marine Mammals of the World. Rome, Italy: United Nations Environment Programme and Food and Agriculture Organization of the United Nations.

Mate, B. 1979. California Sea Lion. Pp. 5-8 in FAO Advisory Committee on Marine Resource Research Working Party on Marine Mammals, ed. Mammals in the Sea vol. 2 Pinniped Species Summaries and Report on Sirenians. Rome, Italy: Food and Agriculture Organization of the United Nations.

Mate, B. 1978. California Sea Lion. Pp. 172-177 in D Haley, ed. Marine Mammals of Eastern North Pacific and Artic Waters. Seattle, Washington: Pacific Search Press.

Odell, D. 1981. California Sea Lion - *Zalophus californianus*. Pp. 67-97 in S Ridgway, R Harrison, eds. Handbook of Marine Mammals: vol. 1: The Walrus, Sea Lions, Fur Seals and Sea Otter. London: Academic Press.

Riedman, M. 1990. The Pennipeds: Seals, Sea Lions, and Walruses. Berkeley, California: University of California Press.

Scheffer, V. 1958. Seals, Sea Lions and Walruses: A Review of the Pinnipedia. Stanford California: Stanford University Press.

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