Mammal Species of the World
- Original description: "In Bory de Saint-Vincet (ed.), Dictionnaire Classique d'Histoire Naturelle. Paris, 13:420."
Large numbers of adult and subadult males and juveniles undertake a post-breeding season migration north from the major rookeries in southern California and Baja California and winter from central California to Washington State. Smaller numbers of animals migrate to British Columbia and southeast Alaska, making it to the northern Gulf of Alaska, Alaska Peninsula, and eastern Aleutian Islands. Other animals appear to remain in the Gulf of California year round and do not undertake long migrations.
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 )
occurs (regularly, as a native taxon) in multiple nations
Global Range: Coastal North Pacific, Mazatlan and Baja California to Vancouver Island (males in fall and winter); breeds on San Miguel, San Nicolas, Santa Barbara, and San Clemente islands in southern California; largest breeding colony is on San Miguel Island; a few pups are born occasionally at South Farallon and Ano Nuevo islands off central California; in Mexico, breeds on the Coronados, Guadalupe, San Martin, Cedros, and San Benito islands off the Pacific coast of Baja California, and there are many smaller colonies on islands in the Gulf of California (Keith et al. 1984, Reeves et al. 1992). Galapagos and eastern Asian populations, sometimes included in this species, are now regarded as distinct species.
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
Length: 250 cm
Weight: 300000 grams
Size in North America
Average: 2.1 m males; 1.6 m females
Range: 2-2.5 m males; 1.6-1.8 m females
Average: 375 kg males; 94 kg females
Range: 350-400 kg males; 90-120 kg females
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
Habitat and Ecology
Age of maturity for both sexes is about 4-5 years. Females produce one pup each year after a gestation of about 11 months. A long term mark-resighting study (1980-2006) recorded a maximum observed longevity of 19 years for males and 25 years for females (Hernandez-Camacho et al. in press). Age-specific birth rates vary among age classes; 5 yr-old females show 0.59, females between 6 and 15 year-old exhibit 0.79 (Melin 2002; Hernandez-Camacho et al. in press), and between 16-25 year-old show decreased birth rate between 0.35 and 0.11 (Hernandez-Camacho et al. in press).
Pupping and breeding take place from May through July. Pupping starts earlier in the Gulf of California (May 8) than in California (May 20) and the duration of the breeding season is longer in the Gulf (13 weeks) than in California (9.5 weeks) (Garcia-Aguilar and Aurioles-Gamboa 2003). Males are highly polygynous and hold territories both on land and in shallow water near shore for periods up to 45 days. Females stay ashore with their newborn pups for about seven days before they depart for the first of many foraging trips that usually last 2-3 days and are followed by attendance with the pup at the rookery for 1-2 days. Most pups are weaned at 12 months of age. However, some pups continue to receive maternal care as yearlings and 2-3year olds (Newsome et al. 2006).
The diving pattern of lactating adult females is consistent with that of a number of other otariid species. The deepest dive recorded was to approximately 274 m and the longest dive lasted just under ten minutes. Typical feeding dives are shallower than 80 m, and last less than three minutes (Feldkamp et al. 1989; Antonelis et al. 1990). Lactating adult females are active for most of the time they are at sea and feeding bouts occur during the day and at night, with peaks of activity at dawn and dusk. The fact that feeding dives occur in bouts suggests that California sea lions are frequently exploiting patches of prey (Weise and Costa 2007).
California Sea Lions are generally found in waters over continental shelf and slope zones; however, they occupy several islands far offshore in deep oceanic areas, such as Guadalupe Island. They frequent coastal areas including bays, harbours, and river mouths.
California Sea Lions feed on a wide variety of prey, but usually maintain a preference for 4-5 species at each location, often taking what is abundant locally or seasonally in the areas they occupy (Lowry et al. 1990; Garcia-Rodriguez and Aurioles-Gamboa 2004). A lower diversity of prey is taken outside the breeding season, when many animals disperse over large areas, as opposed to during the breeding season, when preferred prey can be reduced by intense foraging activity in small areas within travelling range of the rookeries (Lowry 1991). Principle prey taken by California Sea Lions in the Pacific includes: Pacific whiting, market squid, red octopus, jack and Pacific mackerel, blacksmith, juveniles of various species of rockfish, herring, northern anchovy, and salmon (Antonelis et al. 1984; Lowry et al. 1990; Lowry 1991). Sea lions in the Gulf of California have northern anchovy, Pacific whiting, and rockfish as prey in common with animals in the Pacific and also take various species of midshipmen, myctophids and bass, as well as sardines, largehead hairtail and Eastern Pacific flagfin (Aurioles-Gamboa et al. 1984; Garcia-Rodriguez and Aurioles-Gamboa 2004). Because of their boldness and taste for commercially-important fish species, such as salmon and rockfish that are easily taken from fishing lines (DeMaster et al., 1985) California sea lions are considered a nuisance by many sport and commercial fishermen. They will also ascend rivers following spawning runs of anadromous fish and take advantage of man-made structures such as canal locks and fish ladders that concentrate prey.
Predators of California Sea Lions include Killer Whales, sharks, Coyotes and feral dogs, and until they were recently extirpated from the California Channel Islands, bald eagles were known to take young pups.
Habitat Type: Marine
Comments: Coastal waters. Hauls out on rocky and sandy beaches, primarily on islands. Young are born in rookeries on rocky and sandy beaches, primarily on islands.
Water temperature and chemistry ranges based on 2769 samples.
Depth range (m): 0 - 139.2
Temperature range (°C): 8.622 - 26.131
Nitrate (umol/L): 0.038 - 26.169
Salinity (PPS): 30.381 - 35.304
Oxygen (ml/l): 2.414 - 6.583
Phosphate (umol/l): 0.330 - 2.161
Silicate (umol/l): 1.436 - 34.422
Depth range (m): 0 - 139.2
Temperature range (°C): 8.622 - 26.131
Nitrate (umol/L): 0.038 - 26.169
Salinity (PPS): 30.381 - 35.304
Oxygen (ml/l): 2.414 - 6.583
Phosphate (umol/l): 0.330 - 2.161
Silicate (umol/l): 1.436 - 34.422
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
After the breeding season (August-September) some adult and subadult males move northward and overwinter as far north as British Columbia; return south March-May. Males from Baja California rookeries arrive in southern California in December-January (Reeves et al. 1992). Migratory status of females and young unclear.
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 )
Comments: Opportunistic feeder. Feeds on squid, octopus, and a various fishes, including herring, anchovy, whiting, mackerel, sardines, hake, rock-fish, etc. Males do not feed during breeding season. Lactating females at San Miguel Island forage with 100 km of rookery, in highly productive upwelling areas; most feeding dives are relatively shallow (26-74 m) (Reeves et al. 1992).
See Riedman, 1990.
This list may not be complete but is based on published studies.
Known prey organisms
Based on studies in:
USA: California, Southern California (Marine, Sublittoral)
This list may not be complete but is based on published studies.
- Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2006. The Animal Diversity Web (online). Accessed February 16, 2011 at http://animaldiversity.org. http://www.animaldiversity.org
- T. A. Clark, A. O. Flechsig, R. W. Grigg, Ecological studies during Project Sealab II, Science 157(3795):1381-1389, from p. 1384 (1967).
10,000 to >1,000,000 individuals
Comments: U.S. population was estimated at more than 160,000 in the mid-1990s (NMFS, Federal Register, 15 March 1996).
Gregarious at all seasons. Predators include killer whales and sharks, though these have little impact on populations.
Life History and Behavior
Perception Channels: tactile ; chemical
Comments: Feeds mostly at night, spends the morning and mid-day sleeping on beaches.
The oldest recorded wild Z. californianus lived 17 years (Mate, 1979).
Status: wild: 17 (high) years.
Status: captivity: 31 (high) years.
Status: wild: 17.0 years.
Status: captivity: 30.0 years.
Lifespan, longevity, and ageing
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
Males establish breeding territories after arrival of females. Single pups are born mainly in late June in California, late May-January in Galapagos. Females mate 3-4 weeks after giving birth, then make periodic trips to sea to feed. Young are weaned generally in 4-8 months in California but frequently after more than a year and sometimes three years in the Galapagos. Females sexually mature at about 4 years, may live up to 25 years; most adult females breed annually. Males first breed probably at 9-10 years.
Molecular Biology and Genetics
Barcode data: Zalophus californianus
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Zalophus californianus
Public Records: 2
Specimens with Barcodes: 5
Species With Barcodes: 1
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
IUCN Red List Assessment
Red List Category
Red List Criteria
IUCN Evaluation of the California Sea Lions, Zalophus californianus
Prepared by Pinniped Specialist Group
A. Population reduction Declines measured over the longer of 10 years or 3 generations
A1 CR > 90%; EN > 70%; VU > 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.
Exploitation during the 19th and 20th centuries caused population reductions. The distribution range has not changed since the exploitation era but population numbers have increased mainly in California where the population estimate is around 238,000. The population in Mexico occupies both side of the Baja California Peninsula: the west coast has an estimated population of 75,000 – 87,000, whereas the Gulf of California population is near 30,000. The total population of California sea lions is therefore around 355,000 individuals. The population in California is reaching carrying capacity. Some colonies in the Central Gulf of California have declined by approximately 35% in the last 15 years.
A2, A3 & A4 CR > 80%; EN > 50%; VU > 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
California Sea Lions are abundant; they are likely reaching carrying capacity in California.
A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1l.
A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.
No population reduction is inferred in the near future in California or in west coast Baja California. However, some rookeries in the Gulf of California are declining and are likely to continue to decline in the near future.
B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR < 100 km²; EN < 5,000 km²; VU < 20,000 km²
Considering recent, frequent sightings of California Sea Lion in the Gulf of Alaska and the end of the Gulf of California as the northern and southern limits of its occurrence (around 6800 km) and a typical coastal distribution of 50 km, the EOO of California Sea Lions is around 340,000 km².
B2. Area of occupancy (AOO): CR < 10 km²; EN < 500 km²; VU < 2,000 km²
The AOO for the California Sea Lion, determined for the locations in which they breed (around 2,845 km) and 50 km offshore is about 142,250 km².
AND at least 2 of the following:
(a) Severely fragmented, OR number of locations: CR + 1; EN < 5; VU < 10
(b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.
The California Sea Lion has 13 rookeries from the Channel Islands to the south of Baja California and 13 rookeries inside the Gulf of California. The populations in California and Baja California show population declines during severe El Niño event, but they tend to recover to previous levels within 4-5 years. The Gulf of California does not show such fluctuations; it is genetically isolated from the remaining geographic distribution.
C. Small population size and decline
Number of mature individuals: CR < 250; EN < 2,500; VU < 10,000
AND either C1 or C2:
C1. An estimated continuing decline of at least: CR + 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future)
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR < 50; EN < 250; VU < 1,000
(a ii) % individuals in one subpopulation: CR = 90–100%; EN = 95–100%; VU = 100%
(b) Extreme fluctuations in the number of mature individuals.
D. Very small or restricted population
Number of mature individuals: CR < 50; EN < 250; VU < 1,000 AND/OR restricted area of occupancy typically: AOO < 20 km² or number of locations < 5
E. Quantitative Analysis
Indicating the probability of extinction in the wild to be: Indicating the probability of extinction in the wild to be: CR > 50% in 10 years or 3 generations (100 years max.); EN > 20% in 20 years or 5 generations (100 years max.); VU > 10% in 100 years
Some quantitative analysis for the probability of extinction is available for rookeries of California sea lions in the Gulf of California, indicating that at least one of the 4 clusters of rookeries shows a risk for being CR > 50% in 15 years.
Listing recommendation — The California Sea Lion population is abundant and probably reaching carrying capacity in most of its wide geographic distribution. A category of Least Concern should be assigned for the global status. However, the Gulf of California Sea Lion population is genetically isolated, relatively small and some colonies have shown recent declines. Some of the local stocks in the Gulf of California should be considered Near Threatened.
National NatureServe Conservation Status
Rounded National Status Rank: N5N - Secure
Rounded National Status Rank: N4 - Apparently Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Exploitation during the 19th and 20th centuries caused population reductions. The distribution range has changed little since exploitation era but population numbers have increased mainly in California, where the estimate is around 238,000 individuals (Carretta et al. 2007). The population in Mexico occupies both side of the Baja California Peninsula: the west coast has an estimated population of 75,000 – 87,000 (Lowry and Maravilla 2005), whereas the Gulf of California populations is near 30,000 (Szteren et al. 2006). Total population of California sea lions is therefore around 355,000 individuals.
The California Sea Lion population is apparently reaching carrying capacity in the USA (Carretta et al. 2007) whereas in the Gulf of California the population has decreased by ~20% in the last 15 years (Szteren et al. 2006). The California Sea Lion has 13 rookeries from the Channel Islands to the south of Baja California and 13 rookeries inside the Gulf of California. The population in California and Baja California show declines during severe El Niño events that usually return to previous levels within 4-5 years. The Gulf of California does not show this sort of marked fluctuations but it is genetically isolated from the remaining geographic distribution (Maldonado et al. 1985; Schramm 2003, Bowen et al. 2005).
Global Short Term Trend: Increase of 10 to >25%
Comments: Numbers have increased in southwestern Canada since the early 1970s (Bigg 1988). Total U.S. population increased steadily over the past two decades (NMFS, Federal Register, 15 March 1996). The number of pups born in the Channel Islands increased from about 19,000 in 1989 to 25,000 in 1990 and 31,000 in 1991 (Reeves et al. 1992).
California Sea Lion mortality occurs in conflicts with fisheries, by poaching, and through entanglement in marine debris (Stewart and Yochem 1987; Aurioles-Gamboa et al. 2003). Prey availability is greatly reduced during El Niño events and large numbers of pups born during these periods die of starvation, as do weaker animals from all age classes (Francis and Heath 1991). The sea lion rookeries inside the Gulf of California do not appear to be greatly effected by El Niño events (Aurioles and Le Boeuf 1991; Wielgus et al. in press).
California Sea Lions accumulate pollutants through the food chain, and large amounts of DDT, and PCBs discharged in the past, continue to accumulate in coastal marine food chains that include this species. Additionally, large amounts of agricultural and urban runoff and waste continue to be discharged into coastal marine habitats annually from numerous sources; this may have effects on sea lion immune systems and overall health. California Sea Lions do sometimes die of paralytic shellfish poisoning caused by domoic acid, a biotoxin produced by diatom blooms that enter the food web through planktivorous fish such as herring and sardine (Silvagni et al. 2005). California Sea Lions experience mortality from a number of diseases, including some such as leptospirosis contracted from terrestrial animals. They are at risk of exposure to additional diseases from contact with feral and domestic dogs and other terrestrial animals.
Comments: In the early 1980s, as many as 1500/year may have died as a result of entanglement in gill nets or from being shot by commercial fishermen; such mortality continues at an unknown rate. In the late 1960s and early 1970s, premature births were observed in California, evidently the result of DDT and PCB contamination and viral and bacterial infections (Reeves et al. 1992).
Relevance to Humans and Ecosystems
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
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
- 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.
- 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.
Comments: Widely displayed in zoos, aquaria, and circuses.
With increasing populations in southwestern Canada, there have been increased complaints from fisherman about interference with fishing operations and damage to gear and stocks of herring, squid, and cod (Bigg 1988). At Chittendon Locks near Seattle, Washington, since the 1980s, adult males have been a problem by preying on already depleted steelhead populations. Success of translocations of "problem" sea lions preying on steelhead near Seattle, Washington, has been limited by the return of some of the translocated individuals, from release points as far as southern California (Reeves et al. 1992).
See Reeves et al. (1992) for history of exploitation.
California sea lion
The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America. It is one of five species of sea lion. Its natural habitat ranges from southeast Alaska to central Mexico, including the Gulf of California. Sea lions are sexually dimorphic, males are larger than females, and have a thicker neck and protruding 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 white sharks.
California sea lions have a polygynous breeding pattern. From May to August, males establish territories and try to attract females to mate with. 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 of their breeding season, sea lions spend much of their time at sea, but they come to shore to molt.
Sea lions are particularly intelligent and can be trained to perform various tasks. Because of this, California sea lions are commonly found in public displays in zoos, circuses and oceanariums, where they are known as the classic "seals," and are trained by the US Navy for certain military operations. The International Union for Conservation of Nature (IUCN) lists the species as Least Concern due to its abundance. Predation by California sea lions on threatened or endangered salmon species at Bonneville Dam has resulted in more than 50 of them being killed by state officials.
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." This refers to the protruding sagittal crest of the males, which distinguishes members of the genus.
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. The lineages of the California and Japanese sea lion appear to have split off 2.2 million years ago during the Pliocene. The California sea lion differs from the Galapagos sea lion in its greater sexual dimorphism. The Steller sea lion is the closest extant relative of the Zalophus sea lions, being a sister taxon.
Appearance, physiology, and movement
Being sexually dimorphic, California sea lions differ in size, shape, and coloration between the sexes. Males are typically around 2.4 m (7.9 ft) long and weigh up to 350 kg (770 lb), while females are typically around 1.8 m (5.9 ft) and weigh up to 100 kg (220 lb). Females and juveniles have a tawny brown pelage, although they may be temporarily light gray or silver after molting. The pelage of adult males can be anywhere from light brown to black, but is typically dark brown. The face of adult males may also be light tan in some areas. Pups have a black or dark brown pelage at birth. Although the species has a slender build, adult males have robust necks, chests, and shoulders. Adult males also have a protruding crest which gives them a "high, domed forehead"; it is tufted with white hairs. They also have manes, which are less developed than those of adult male South American and Steller sea lions. Both sexes have long, narrow muzzles.
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. 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. 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. Sea lions may travel at speeds of around 10.8 km/h (6.7 mph), 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.
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. Sea lions have fairly acute underwater hearing, with a hearing range of 0.4–32 kHz. 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.
Range and habitat
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. 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. 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.
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. 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 the Bonneville Dam in the Columbia River. 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.
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. They mostly forage near mainland coastlines, the continental shelf, and seamounts. They may also search along the ocean bottom. 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. Sea lions sometimes follow dolphins and exploit their hunting efforts. Adult females feed between 10–100 km (6.2–62.1 mi) from shore. Males may forage as far as 450 km (280 mi) from shore when water temperatures rise. 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. The sea lions may respond to the dorsal fin of a killer whale and remain vigilant, even when encountering resident fish-eating pods. 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. Sea lions that are attacked in the hindquarters are more likely to survive and make it to the shore.
Reproductive behavior and parenting
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 mostly underwater, particularly those near steep cliffs. Sea lions that fail to establish a territory are driven out to sea or gather at a nearby beach.
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. 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 though different territories. They avoid males that are too aggressive or energetic. Males are usually unable to prevent females from leaving their territories, particularly in water. 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.
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. Females remain with their pups on shore 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 on shore tend to gather in nurseries to socialize and play. 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. Older pups may sometimes join their mothers during their foraging trips. 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. Pups are weaned by a year but can continue to suckle for another year.
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.
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. California sea lions can produce vocalizations underwater. These include "whinny" sounds, barks, buzzings, and clicks.
Outside of the breeding season, males migrate to the northern ends of the species range to feed, while females forage near the breeding rookeries. 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.
Intelligence and trainability
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. 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. In 2011, a California sea lion named "Ronan" was recorded bobbing its head in synchronization to musical rhythms. This "rhythmic entrainment" was previously seen only in humans, parrots and other birds possessing vocal mimicry.
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 trick for the public. However, its memory allows it to perform a trick even after three months of resting. 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.
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. Organizations like PETA believe that since operations put the animals in danger. However, the Navy insists that the sea lions are removed once their mission is complete.
The IUCN lists the California sea lion as Least Concern due to "its large and increasing population size." The estimated population is 238,000–241,000 for the US 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. Off the US coast, 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.
In the United States, the California sea lion is protected on the 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. Applications have been granted for removal of several individual sea lions at Ballard Locks and at the Bonneville Dam, where up to 92 sea lions can be killed each year for a 5-year period. 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.
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.
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Names and Taxonomy
Comments: Zalophus japonicus (Japanese sea lion) and Z. wollebaeki (Galapagos sea lion) sometimes have been regarded as subspecies of Z. californianus. Wozencraft (in Wilson and Reeder 2005) listed them as distinct species.
The English name for sea lions has been inconsistently rendered as sea lion, sealion, and sea-lion (Rice 1998, Wozencraft, in Wilson and Reeder 2005).