California sea lion
California sea lion. Source: Biopix
The California sea lion (Scientific name: Zalophus californianus) is one of 16 species of marine mammals in the family of eared seals which include sea lions and fur seals. Together with the families of true seals and Walruses, Eared seals form the group of marine mammals known as pinnipeds. California sea lions are a highly social and intelligent species that is well adapted to a semi-aquatic life-style. They are widely used in educational programs in zoos and aquariums throughout the world because of their agility and trainability.
Eared seals differ from the true seals in having small external earflaps and hind flippers that can be turned to face forwards. Together with strong front flippers, this gives them extra mobility on land and an adult fur seal can move extremely fast across the beach if it has to. They also use their front flippers for swimming, whereas true seals use their hind flippers.
Until recently, it was believed that the Japanese sea lion and Galapagos sea lion were sub-species of the California sea lion. However, recent studies of DNA suggest that these are three separate species.
 California sea lion. Source: David Corby/Wikipedia |
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Conservation Status  |
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Scientific Classification Kingdom: Anamalia (Animals) |
Contents
Physical Description
Male and female California sea lions exhibit pronounced sexual dimorphism. differing significantly in overt appearance. Males are substantially larger than females and have an enlarged sagittal crest (a ridge of bone running lengthwise alongthe top of the skull), which is usually topped with white fur.
Newborn pups average 75 cm in length and are between five to six kg in body mass. Adult males average 2.2 meters in length and 275 kg in weight but can reach length of 2.4 meters and weights of 390 kg. Females are smaller, averaging 1.8 meters in length and 91 kg in weight but can reach lengths of two meters and weights of 110 kg . The California sea lions that occur in Mexico appear are smaller than those found in California
The adult males are generally dark brown with a lighter belly and side coloring, whereas the females can appear more tan colored. The pups are born with a blackish-brown coat which moults after a month and is replaced with a light brown coat. This coat is shed after four or five months and replaced with the adult coat..
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.
 California sea lions at Pier 39, San Francisco, USA. Source: Reywas92/Wikipedia |
 California sea lion. Source:Tanya Dewey/Animal Diversity Web/Encyclopedia of Life |
 Distribution of the Californian sea lion. (dark blue = breeding colonies; light blue = non-breeding individuals; red = Galapagos sea lion, which was until recently held to be a subspecies). Source: Mirko Thiessen/Wikipedia |
Reproduction
California sea lions tend to breed on islands or remote beaches of the Pacific Ocean coastal zone. The breeding season starts in May, at which time adult males begin to fight for a territory.A male consistently occupies a territory until factors change and cause him to be displaced. Typical occupation time is approximately two weeks. Although few California sea lion males remain at their site for longer, a male may maintain his territory for up to 45 days depending on other competitive males and on fat reserves.
Successful males guard their territory and maintain boundaries with routine displays and frequent barking. 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. Most males are unsuccessful in territorial establishment and retreat to the sea, or to proximate bachelor beaches.
California sea lions exhibit moderate to extreme polygyny and tend to live in colonies of a few males and many females. Female California sea lions exhibit mate choice, by "respond[ing] differently to the attempts of various males".
Females give birth to a single pup throughout May and June and are ready to mate again about 28 days after giving birth, although this interval is more variable among the population in Mexico. The peak breeding season occurs in early July. The total gestation period is about 11 months. Thus mostbirths occur from mid-May to mid-June with the majority of pups born in mid-June.
The mothers spend the first week after birth with their pup and then begin alternating feeding trips at sea (two to three days) with suckling bouts on land (one to two days), until the pup is weaned. The lactation period in California sea lions 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. California sea lions provide more lengthy maternal care for female offspring than for male offspring, yet during lactation both males and females have equal access and receive equal resources.
The mothers and pups recognise each other after separation by sound and smell. The breeding season ends in August after which time most males migrate north and the females and juveniles disperse, but stay close to the breeding islands. California sea lions reach sexual maturity between four and five years of age. However, males will typically fail to hold a territory until they are older.
Lifespan/Longevity
The oldest recorded wild California sea lion lived 17 years. In captivity, the oldest recorded California sea lion lived to be 31 years old. The age of California sea lions can be determined by counting the number of rings on cross sections of its teeth
Behavior
The California sea lion is a highly gregarious species, hauling out in large groups, although tending to feed individually or in small groups, unless large quantities of food are present. They feed on a large number of different fish species (including some commercial species), such as northern anchovies, pacific whiting, mackerel and are known to also take some cephalopod species. Dives usually last about two minutes, but can last up to ten minutes, and average depths of 26 to 98 metres, although the specie is capable of attaining diving depths of 274 meters and can reach speeds of 15 to 20 miles per hour while swimming. Like certain other marine mammals, California sea lions use a system of echo-location to find food, orient themselves, and navigate underwater. A California sea lion sometimes adopts and fosters a pup that has been abandoned by its birth-mother.
The normal body temperature of California sea lions is 37.5 degrees Celsius. Because California sea lions cannot sweat or pant, in order to thermo-regulate they must change their position in the exterior environment. For example, if the air temperature increases they seek cooler areas, such as water.
Pups exhibit many different play behaviors including mock fighting.
Distribution of the Californian sea lion. (dark blue = breeding colonies; light blue = non-breeding individuals; red = Galapagos sea lion, which was until recently held to be a subspecies). Source: Mirko Thiessen/Wikipedia Distribution
Found from British Columbia in Canada south to Baja in Mexico, including the Gulf of California. California sea lions breed mainly on offshore islands from southern California's Channel Islands south to Mexico,including Baja and Tres Marias Islands, in the Galapagos Islands and in the southern Sea of Japan. The populations in each area do not interact with other populations and therefore are considered subspecies. California sea lions tend to seasonally migrate long distances. Males usually migrate north to British Columbia after the breeding season
Habitat
Breeding occurs on sandy beaches and rocky areas of remote islands where there is easy access to shade, water for cooling down and plenty of food. California sea lions generally fish in open waters along the Pacific coast, but are increasingly being found up rivers and often congregate on man-made structures such as jetties, piers, offshore buoys and oil platforms.
Feeding 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, California sea lions hunt in larger groups. California sea lions 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. Prey taken include: cephalopods, anchovies, herring, Pacific whiting, rockfish, hake, salmon, squid and octopuses.
Conservation Status
The California sea lion is currently classified as Lower Risk / Least Concern on the IUCN Red List and at present the population is quite capable of recovering from limited conflict with humans and the occasional El Nino event. As long as there is enough food, and some level of protection remains, it is thought that there is no immediate threat to the survival of the California sea lion. The extinction of the Japanese sea lion, however, reminds us that there can be limits to the recovery of populations from high mortality, especially for the smaller population in Mexico, where human interaction combined with natural stress may make recovery more difficult
California sea lions are well protected in most areas. Occasionally, they are trapped with a permit for display in zoos, aquariums, and circuses. 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.From 1983 to 1984, California sea lions 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.
Until recently, it was believed that the Japanese sea lion and Galápagos sea lion were sub species of the Californian sea lion and recognized as follows:
- Japanese sea lion, Zalophus californianus ssp. japonicus (extinct)
- Galápagos sea lion, Zalophus californianus ssp. wollebaeki (vulnerable)
- Californian sea lion, Zalophus californianus ssp. californianus (no special status).
However, recent studies of DNA suggest that these are three separate species.
Threats
The California sea lion faces a number of threats, most notably through human-animal conflict and climate change. In the 19th and early 20th centuries California sea lions were extensively killed for commercial purposes, and although later afforded some protection, were still killed in large numbers until hunting was banned between 1969 and 1972. Population numbers have now recovered, but growing numbers are being killed in fishing nets. California sea lions are also increasingly thought to be damaging commercial fish stocks and in 1999 the federal National Marine Fisheries Service released a report recommending that Congress allow wildlife managers to kill California sea lions that are preying on endangered fish species. California sea lions are also negatively affected by El Nino, which causes a shortage in food supply and increased mortality. Other causes of mortality include infection, disease, poisoning, pollution and toxic phytoplankton blooms.
Economic Importance for Humans
California sea lions were historically 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 in zoos andaquariumsthroughout the world because of their agility and trainability. They are charming ambassadors for their sea lion cousins.
California sea lions are thought by some to reduce stocks of fish such as salmon. They also may interfere with nets used by fishermen.
Image Source: Wikimedia Commons
Further Reading
- Zalophus californianus (Lesson, 1828) Encyclopedia of Life (accessed April 8, 2009)
- californianus, Price, R., 2002, Animal Diversity Web (accessed April 8, 2009)
- Zalophus, Seal Conservation Society (accessed April 3, 2009)
- The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984
- Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
- Marine Mammal Research: Conservation beyond Crisis, edited by John E. Reynolds III, William F. Perrin, Randall R. Reeves, Suzanne Montgomery and Timothy J. Ragen, Johns Hopkins University Press, 2005 ISBN: 0801882559
- IUCN Red List (January, 2008) http://www.iucnredlist.org/
- Heath, C.B. (2002) California, Galapagos, and Japanese sea lions. In: Perrin, W.F., Wursig, B. and Thewissen, J.G.M. Eds. Encyclopedia of Marine Mammals. Academic Press, San Diego.
- Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899
- California sea lion, MarineBio.org (accessed April 8, 2009)
- Galápagos and Californian sea lions are separate species: Genetic analysis of the genus Zalophus and its implications for conservation management, Wolf, JB; Tautz, D; Trillmich, F, Frontiers in zoology,2007.
