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Lifespan, longevity, and ageing

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Maximum longevity: 35.7 years (captivity) Observations: The total gestation time, of approximately 11.5 months, probably includes a 3 month period of delayed implantation (Ronald Nowak 2003). In the wild, these animals appear to live up to 17 years (Bernhard Grzimek 1990). One wild born male was still alive in captivity at about 35.7 years of age (Richard Weigl 2005).
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Untitled

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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)

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Behavior

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Perception Channels: tactile ; chemical

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Conservation Status

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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).

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Benefits

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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

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Benefits

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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.

Positive Impacts: ecotourism ; research and education

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Trophic Strategy

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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

Primary Diet: carnivore (Piscivore , Molluscivore )

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Distribution

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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).

Biogeographic Regions: nearctic (Native ); pacific ocean (Native )

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Habitat

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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).

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: rivers and streams; coastal

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Life Expectancy

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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).

Range lifespan
Status: wild:
17 (high) years.

Range lifespan
Status: captivity:
31 (high) years.

Average lifespan
Status: wild:
17.0 years.

Average lifespan
Status: captivity:
30.0 years.

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Morphology

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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.

Range length: 2.4 (high) m.

Other Physical Features: endothermic ; bilateral symmetry

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Rebecca Price, University of Michigan-Ann Arbor
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Associations

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See Riedman, 1990.

Known Predators:

  • great white sharks (Carcharodon carcharias)
  • bull sharks (Carcharhinus amboinensis)
  • killer whales (Orcinus orca)
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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Reproduction

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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).

Mating System: polygynous

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 gestation period: 11 months.

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 (male): 4-5 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal )

Average birth mass: 7000 g.

Average gestation period: 259 days.

Average number of offspring: 1.2.

Average age at sexual or reproductive maturity (male)
Sex: male:
1826 days.

Average age at sexual or reproductive maturity (female)
Sex: female:
1095 days.

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.

Parental Investment: female parental care

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Price, R. 2002. "Zalophus californianus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Zalophus_californianus.html
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Rebecca Price, University of Michigan-Ann Arbor
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Biology

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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 California sea lions have been known to dive to well below 200 metres (2). The breeding season starts in May, at which time adult males begin to fight for a territory. Most males are unsuccessful and retreat to the sea, or to bachelor beaches nearby. Successful males guard their territory and maintain boundaries with routine displays and frequent barking. A male may maintain his territory for up to 45 days depending on other competitive males and on fat reserves. 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 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, at about ten to twelve months. The mothers and pups recognise each other after separation by sound and smell (2). 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. Average lifespan is 15 to 24 years with the young reaching sexual maturity at about four to five years. However, males will generally fail to hold a territory until they are older (2).
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Conservation

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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 Niño 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 (2).
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Description

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This highly social and intelligent species is well adapted to a semi-aquatic life-style. California sea lions swim using their fore-flippers and are particularly agile on land as they are able to control their hind flippers independently (3). Male and female California sea lions differ significantly in appearance. Males are substantially bigger than females and have an enlarged sagittal crest, which is usually topped with white fur. The adult males are generally dark brown with a lighter belly and side colouring, whereas the females can appear more tan coloured. 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. The California sea lions found in Mexico appear smaller than those found in California (2).
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Habitat

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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 (2). 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 and piers (5).
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Range

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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 (4).
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Status

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Classified as Least Concern (LC) on the IUCN Red List (1).
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Threats

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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 (6). California sea lions are also negatively affected byEl Niño, which causes a shortage in food supply and increased mortality (2). Other causes of mortality include infection, disease, poisoning, pollution and toxic phytoplankton blooms (2) (6).
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Diagnostic Description

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The California sea lion is the well-known performing "seal" of zoos, circuses, and oceanaria. In both sexes, the muzzle is dog-like and long, slightly tapering to a moderately blunt end. Adult males are substantially more robust and larger than females. In adult males, the sagittal crest creates a high peaked crown. The crest begins to emerge at sexual maturity and, although highly variable, is most prominent in full-grown males. On most males, especially darker individuals, the crest and a corresponding area on the muzzle and around the eyes lighten with age. Females lack a pronounced crest and have a thinner head that slopes more gently to the end of the muzzle. This makes subadult and juvenile males very difficult to distinguish from females.

Colour of California sea lions is highly variable. When dry, the coat of most adult males is dark brown. However, many males do not darken completely, remaining sandy brown on the sides, belly, and rear quarters. Adult females and juveniles are uniformly tan. Pups are born with a thick brownish black lanugo that is generally moulted by the end of the first month. The succeeding light brown juvenile coat is shed 4 to 5 months later, and is replaced by adult coloration. All ages and sexes have contrasting black flippers, naked except for a short stubble of dark fur partially covering the upper surface.

The dental formula is variable, but is usually I 3/2, C 1/1, PC 5/5 (in the California race) or PC 6/5 (in the Galapagos race).

Can be confused with: California sea lions share their range with 3 other otariids (Steller sea lions, and northern fur seal and Guadalupe fur seal). Galapagos sea lions overlap with Galapagos fur seals and South American sea lions. These sea lions can be separated from the similar, but much larger, Steller sea lion and similar sized South American sea lion, on the basis of head and muzzle shape and size, and relative size of the ear pinnae. Additionally fore- and hindflippers are relatively shorter than in the Steller sea lion. (See the Guadalupe, Galapagos, and northern fur seal accounts for more detail on separating California and Galapagos sea lions from fur seals.)

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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Size

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Male California sea lions reach lengths of 2.4 m, and weights of more than 390 kg. Females only reach 2 m, and weigh an average of 110 kg. Newborn pups are about 80 cm long and 6 to 9 kg. There is very little information on the sizes of Galapagos sea lions (estimated weights are 200 kg for males, and 50 to 100 kg for females).
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Brief Summary

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Breeding takes place from May through July (California sea lions), and from May through January (Galapagos sea lions). Males are highly polygynous and hold territories both on land and in shallow water nearshore.In California sea lions, most adult males and many subadults and juveniles of both sexes take part in a post-breeding migration northward from the rookeries. Galapagos sea lions apparently stay around the Galapagos Archipelago all year.

At sea, California sea lions often raft at the surface alone or in groups. Animals in such rafts frequently raise their flippers out of the water. California sea lions often "porpoise" when traveling rapidly at sea, sometimes in large groups. Juveniles and subadults may perform acrobatic and high vertical leaps, and individuals of all ages surf breakers and ride in the wakes of vessels. California sea lions are often seen with a wide variety of dolphin and baleen whale species.California sea lions feed on squid, octopus, and many species of fishes. Because of their taste for commercially important fish species and their boldness, California sea lions are considered a nuisance by many sport and commercial fishermen.

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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Benefits

provided by FAO species catalogs
Currently, there is no significant direct catch of California sea lions. Many sea lions, however, are shot by fishermen and certainly many others are taken incidentally during fishing operations. Set gillnets and driftnets, in particular, appear to be taking large numbers each year. The total population of the California sea lion in 1989 was estimated to be 160 000 and increasing, about equally split between Mexico and the United States. The numbers of Galapagos sea lions are unknown. Unfortunately, the Japanese race of this sea lion is now extinct. IUCN:

Insufficiently known; extinct (Zalophus californianus japonicus only).

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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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California sea lion

provided by wikipedia EN

The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America. It is one of six species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. California sea lions are sexually dimorphic; males are larger than females, and have a thicker neck, and protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by killer whales and great white sharks.

California sea lions have a polygynous breeding pattern. From May to August, males establish territories and try to attract females with which to mate. Females are free to move in between territories, and are not coerced by males. Mothers nurse their pups in between foraging trips. Sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside their breeding season, sea lions spend much of their time at sea, but they come to shore to molt.

Sea lions are particularly intelligent, can be trained to perform various tasks and display limited fear of humans if accustomed to them. Because of this, California sea lions are a popular choice for public display in zoos, circuses and oceanariums, and are trained by the United States Navy for certain military operations. The International Union for Conservation of Nature (IUCN) lists the species as Least Concern due to its abundance. To protect fish, the US states of Oregon and Washington engage in annual kill quotas of sea lions.

Taxonomy

 src=
Lithography by Joseph Smit.

The California sea lion was described by René Primevère Lesson, a French naturalist, in 1828. It is grouped with other sea lions and fur seals in the family Otariidae. Otariids, also known as eared seals, differ from true seals in having external ear flaps, and proportionately larger foreflippers and pectoral muscles. Along with the Galapagos sea lion and the extinct Japanese sea lion, the California sea lion belongs to the genus Zalophus, which derives from the Greek words za, meaning "intensive," and lophus, meaning "crest."[2] This refers to the protruding sagittal crest of the males, which distinguishes members of the genus.[3]

Traditionally, the Galapagos sea lion and Japanese sea lion were classified as subspecies of the California sea lion. However, a genetic study in 2007 found that all three are in fact separate species.[4] The lineages of the California and Japanese sea lion appear to have split off 2.2 million years ago during the Pliocene.[5] The California sea lion differs from the Galapagos sea lion in its greater sexual dimorphism.[3] The Steller sea lion is the closest extant relative of the Zalophus sea lions, being a sister taxon.[6]

Appearance, physiology, and movement

 src=
California sea lion skeleton

Being sexually dimorphic, California sea lions differ in size, shape, and coloration between the sexes. Males are typically around 2.7 m (8.9 ft) long and weigh up to 350 kg (770 lb), while females are typically around 2.1 m (6.9 ft) and weigh up to 100 kg (220 lb).[3] Females and juveniles have a tawny brown pelage,[3] although they may be temporarily light gray or silver after molting.[7] The pelage of adult males can be anywhere from light brown to black, but is typically dark brown.[3] The face of adult males may also be light tan in some areas. Pups have a black or dark brown pelage at birth.[7] Although the species has a slender build, adult males have robust necks, chests, and shoulders.[7] Adult males also have a protruding crest which gives them a "high, domed forehead";[8] it is tufted with white hairs.[3] They also have manes, which are less developed than those of adult male South American and Steller sea lions.[8] Both sexes have long, narrow muzzles.[7]

As an otariid, the California sea lion relies on its foreflippers to propel itself when swimming. This form of aquatic locomotion, along with its streamlined body, effectively reduces drag underwater. Its foreflipper movement is not continuous; the animal glides in between each stroke.[9] The flexibility of its spine allows the sea lion to bend its neck backwards far enough to reach its hindflippers. This allows the animal to make dorsal turns and maintain a streamlined posture.[10] When moving on land, the sea lion is able to turn its hindflippers forward and walk on all fours. It moves the foreflippers in a transverse, rather than a sagittal, fashion. In addition, it relies on movements of its head and neck more than its hindflippers for terrestrial locomotion.[11] Sea lions may travel at speeds of around 10.8 km/h (6.7 mph),[12] and can dive at depths of 274 m (899 ft) and for up to 9.9 minutes, though most dives are typically 80 m (260 ft) and last less than 3 minutes.[13]

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Sea lion swimming underwater

Sea lions have color vision, though it is limited to the blue-green area of the color spectrum. This is likely an adaptation for living in marine coastal habitats.[14] Sea lions have fairly acute underwater hearing, with a hearing range of 0.4–32 kHz.[15] Sea lions rely on their whiskers or vibrissae for touch and detection of vibrations underwater. Compared to the harbor seal, the California sea lion's vibrissae are smoother and less specialized and thus perform less when following hydrodynamic trails, although they still perform well.[16]

Ecology

Range and habitat

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Sea lion rookery on Santa Barbara island

The California sea lion ranges along the western coast and islands of North America, from southeast Alaska to central Mexico. Mitochondrial DNA sequences in 2009 have identified five distinct California sea lion populations: the U.S. or Pacific Temperate stock, the Western Baja California or Pacific Tropical stock, and the Southern, Central, and Northern Gulf of California stocks.[6] The U.S. stock breeds mainly in the Channel Islands, although some breeding sites may be established in northern California, and females are now commonly found there.[1] The Western Baja California stock mainly breeds near Punta Eugenia and at Isla Santa Margarita. The above-mentioned stocks are separated by the Ensenada Front. The stocks of the Gulf of California live in the shallow waters of the north (Northern stock), the tidal islands near the center (Central stock), and the mouth of the bay (Southern stock). The stock status of the sea lions at the deep waters of the central bay has not been analyzed.[6]

Vagrants can reach western north pacific such as on Commander Islands.[17] Although several otariinae have been recorded around the Japanese archipelago in recent years, their exact origins are unclear.[18]

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Sea lions in Santa Cruz, California

During the breeding season, sea lions gather on both sandy and rocky shores. On warm days, they lie closer to the water. At night or in cool weather, they travel farther inland or to higher elevations.[7] Non-breeding individuals may gather at marinas, wharves, or even navigational buoys. California sea lions can also live in fresh water for periods of time, such as near Bonneville Dam, nearly 150 miles (240 km) up the Columbia River.[19] In 2004, a healthy sea lion was found sitting on a road in Merced County, California, almost a hundred miles upstream from the San Francisco Bay and half a mile from the San Joaquin River.[20]

Diet and predation

California sea lions feed on a wide variety of seafood, mainly squid and fish, and sometimes clams. Commonly eaten fish and squid species include salmon, hake, Pacific whiting, anchovy, herring, rockfish, lamprey, dogfish, and market squid.[21] They mostly forage near mainland coastlines, the continental shelf, and seamounts. They may also search along the ocean bottom.[7] California sea lions may eat alone or in small to large groups, depending on the amount of food available. They sometimes cooperate with other predators, such as dolphins, porpoises, and seabirds, when hunting large schools of fish.[22] Sea lions sometimes follow dolphins and exploit their hunting efforts.[3] Adult females feed between 10–100 km (6.2–62.1 mi) from shore.[12] Males may forage as far as 450 km (280 mi) from shore when water temperatures rise.[23] They also have learned to feed on steelhead and salmon below fish ladders at Bonneville Dam and at other locations where fish must queue in order to pass through dams and locks that block their passage.

Sea lions are preyed on by killer whales and large sharks. At Monterey Bay, California sea lions appear to be the more common food items for transient mammal-eating killer whale pods.[24] The sea lions may respond to the dorsal fin of a killer whale and remain vigilant, even when encountering resident fish-eating pods.[25] Sea lions are also common prey for white sharks. They have been found with scars made by attacks from both white sharks and shortfin mako sharks. Sharks attack sea lions by ambushing them while they are resting at the surface.[26] Sea lions that are attacked in the hindquarters are more likely to survive and make it to the shore.[27]

Life history

Reproductive behavior and parenting

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Sea lion rookery

California sea lions breed gregariously between May and August, when they arrive at their breeding rookeries. When establishing a territory, the males will try to increase their chances of reproducing by staying on the rookery for as long as possible. During this time, they will fast, relying on a thick layer of fat called blubber for energy. Size and patience allow a male to defend his territory more effectively; the bigger the male, the more blubber he can store and the longer he can wait. A male sea lion usually keeps his territory for around 27 days. Females have long parturition intervals, and thus the males do not establish their territories until after the females give birth. Most fights occur during this time. After this, the males rely on ritualized displays (vocalizations, head-shaking, stares, bluff lunges, and so on) to maintain their territorial boundaries. Since temperatures can reach over 30 °C (86 °F) during this time, males must include water within their territories. Some territories are underwater, particularly those near steep cliffs.[28] Sea lions that fail to establish a territory are driven out to sea or gather at a nearby beach.[3]

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Sea lion mother with pup

Before mating begins, females gather into "milling" groups of 2–20 individuals. The females in these groups will mount each other as well as the males. These groups begin to disintegrate as the females begin to mate.[3] The territorial and mating system of the California sea lion has been described as similar to a lek system, as females appear to choose their mates while moving through different territories.[29] They avoid males that are too aggressive or energetic. Males are usually unable to prevent females from leaving their territories,[3] particularly in water.[30] Mating may occur outside the rookeries, between non-territorial males and females, as the latter move to and from the mating site. In some rookeries, copulation may be monopolized by a few males, while at others, a single male may sire no more than four pups.[30]

Female California sea lions have a 12-month reproductive cycle, consisting of a 9-month actual gestation and a 3-month delayed implantation of the fertilized egg before giving birth in June or July. Interbirth intervals are particularly long for this species, being 21 days for sea lions off California and more than 30 days for sea lions in the Gulf of California.[30] Females remain with their pups onshore for 10 days and nurse them. After this, females will go on foraging trips lasting as long as three days, returning to nurse their pups for up to a day. Pups left onshore tend to gather in nurseries to socialize and play.[7] When returning from a trip, females call their pups with distinctive calls to which the pups will reply in kind. A mother and pup can distinguish each other's calls from those of other mothers and pups. At first, reunions largely depend on the efforts of the mothers. However, as pups get older, they get more involved in reunions.[31] Older pups may sometimes join their mothers during their foraging trips.[7] Adult male California sea lions play no role in raising pups, but they do take more interest in them than adult males of other otariid species; they have even been observed to help shield swimming pups from predators.[32] Pups are weaned by a year but can continue to suckle for another year.[3]

Communication

Barking sea lions pursuing a boat

California sea lions communicate with a range of vocalizations. The most commonly used one is their characteristic bark. Territorial males are the loudest and most continuous callers, and barks are produced constantly during the peak of the breeding season. Sea lions bark especially rapidly when excited. The barks of territorial and non-territorial males sound similar, although those of the former are deeper. Males may bark when threatening other males or during courtship. The only other vocalization made by territorial males is a "prolonged hoarse grunt sound" made when an individual is startled by a human. This vocalization is also made by groups of non-reproductive males.[33]

Female sea lions are less vocal. Their barks, high-pitched and shorter than those made by males, are used in aggressive situations. Other aggressive vocalizations given by females include the "squeal", the "belch", and the "growl". The sound a female sea lion gives when calling her pups is called a "pup-attraction call", described as "loud" and "brawling". Pups respond with a "mother-response call", which is similar in structure. Pups will also bleat or bark when playing or in distress.[33] California sea lions can produce vocalizations underwater. These include "whinny" sounds, barks, buzzings, and clicks.[34]

Nonbreeding activities

Outside the breeding season, males migrate to the northern ends of the species range to feed, while females forage near the breeding rookeries.[3] Sea lions can stay at sea for as long as two weeks at a time. They make continuous dives, returning to the surface to rest. Sea lions may travel alone or in groups while at sea and haul-out between each sea trip. Adult females and juveniles molt in autumn and winter; adult males molt in January and February. Gulf of California sea lions do not migrate; they stay in the Gulf year-round.[30]

Intelligence and trainability

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Zak, a 375 lb (170 kg) Navy sea lion leaps back into the boat after a harbor-patrol training mission.

Marine biologist Ronald J. Schusterman and his research associates have studied sea lions' cognitive ability. They have discovered that sea lions are able to recognize relationships between stimuli based on similar functions or connections made with their peers, rather than only the stimuli's common features.[35] Sea lions have demonstrated the ability to understand simple syntax and commands when taught an artificial sign language. However, the sea lions rarely used the signs semantically or logically.[36] In 2011, a California sea lion named Ronan was recorded bobbing her head in synchronization to musical rhythms.[37] This "rhythmic entrainment" was previously seen only in humans, parrots and other birds possessing vocal mimicry.[38]

Captive sea lion performing
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A California sea lion at Central Park Zoo. It has climbed to the edge of its tank awaiting feeding, showing awareness of its regular feeding time.

Because of their intelligence and trainability, California sea lions have been used by circuses and marine mammal parks to perform various tricks such as throwing and catching balls on their noses, running up ladders, or honking horns in a musical fashion. Trainers reward their animals with fish, which motivates them to perform. For ball balancing, trainers toss a ball at a sea lion so it may accidentally balance it or hold the ball on its nose, thereby gaining an understanding of what to do. A sea lion may go through a year of training before performing a behavior for the public. However, its memory allows it to perform a behavior even after three months of resting.[32] Some organizations, such as the Humane Society of the United States and World Animal Protection, object to using sea lions and other marine mammals for entertainment, claiming the tricks are "exaggerated variations of their natural behaviors" and distract the audience from the animal's unnatural environment.[39]

The California sea lion is used in military applications by the U.S. Navy Marine Mammal Program, including detecting naval mines and enemy divers. In the Persian Gulf, the animals can swim behind divers approaching a US naval ship and attach a clamp with a rope to the diver's leg. Navy officials say the sea lions can do this in seconds, before the enemy realizes what happened.[40] Organizations like PETA believe that such operations put the animals in danger.[41] However, the Navy insists that the sea lions are removed once their mission is complete.[42]

Status

Photo of sea lions crowded together on dock
Hundreds of California sea lions bask on Pier 39 in San Francisco, where they are welcomed as a tourist attraction.

The IUCN lists the California sea lion as Least Concern due to "its large and increasing population size."[1] The estimated population is 238,000–241,000 for the U.S. or Pacific Temperate stock, 75,000–85,000 for the Western Baja California or Pacific Tropical stock, and 31,393 for the population in the Gulf of California.[6] Off the Pacific coast of the United States, sea lions are so numerous that they are close to carrying capacity, while the Gulf of California population declined by 20% by 2008. Sea lions may be killed when in conflict with fishermen, by poaching, and by entanglements in man-made garbage. They are also threatened by pollutants like DDT and PCB which accumulate in the marine food chain.[1]

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Shooting sea lions, ca. 1870s

In the United States, the California sea lion is protected on the federal Marine Mammal Protection Act (MMPA), passed in 1972, which outlaws hunting, killing, capture, and harassment of the animal. In 1994 an amendment to the Act allowed for the possibility of limited lethal removal of pinnipeds preying on endangered salmonids should the level of predation be documented to have a significant adverse impact on the decline or recovery of ESA-listed salmonids.[43] Applications have been granted for removal of several individual sea lions at Ballard Locks[44] and at the Bonneville Dam, where up to 92 sea lions can be killed each year for a 5-year period.[45] Critics have objected to the killing of the sea lions, pointing out that the level of mortality permitted as a result of recreational and commercial fisheries in the river and as part of the operation of hydroelectric dams pose a greater threat to the salmon.[46]

These animals exploit more man-made environments like docks for haul-out sites. Many docks are not designed to withstand the weight of several resting sea lions which cause major tilting and other problems. Wildlife managers have used various methods to control the animals and some city officials have redesigned docks so they can better withstand them.[47][48]

2015 Californian shore sea lions pups crisis

In January and February 2015, 1450 malnourished or sick sea lion pups were found along stretches of the California coast, and estimations give a higher number of dead pups. The National Oceanic and Atmospheric Administration has pointed to unprecedentedly warm Pacific coastal waters, related to Pacific decadal oscillation and El Niño, as the likely cause. Elevated water temperatures reduced the abundance of anchovies, sardines and mackerel, principal components of the sea lion pup diet during nursery season.[49] This caused many sea lion pups to starve, while others died when they took to open waters in search of food at too early an age.[50] Several months earlier, in the summer of 2014, a large number of Cassin's auklet chicks died during the fledging period due to similar circumstances brought about by elevated water temperatures.[51]

Oregon and Washington state governments annual killings

In November 2018, the State of Oregon obtained a permit to kill 93 sea lions per year below Willamette Falls. Under a similar program, Oregon and Washington had killed over 150 sea lions on the Columbia River by January 2019.[52][53]

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California sea lion: Brief Summary

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The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America. It is one of six species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. California sea lions are sexually dimorphic; males are larger than females, and have a thicker neck, and protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. Sea lions feed on a number of species of fish and squid, and are preyed on by killer whales and great white sharks.

California sea lions have a polygynous breeding pattern. From May to August, males establish territories and try to attract females with which to mate. Females are free to move in between territories, and are not coerced by males. Mothers nurse their pups in between foraging trips. Sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside their breeding season, sea lions spend much of their time at sea, but they come to shore to molt.

Sea lions are particularly intelligent, can be trained to perform various tasks and display limited fear of humans if accustomed to them. Because of this, California sea lions are a popular choice for public display in zoos, circuses and oceanariums, and are trained by the United States Navy for certain military operations. The International Union for Conservation of Nature (IUCN) lists the species as Least Concern due to its abundance. To protect fish, the US states of Oregon and Washington engage in annual kill quotas of sea lions.

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