See Riedman, 1990.
Known Predators:
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
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.
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
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 )
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)
Perception Channels: tactile ; chemical
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
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
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 )
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
The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America. It is one of six species of sea lions. 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 a protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. California sea lions feed on a number of species of fish and squid, and are preyed on by orcas 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. California sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside their breeding season, California sea lions spend much of their time at sea, but they come to shore to molt.
California 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 California sea lions.
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."[3] This refers to the protruding sagittal crest of the males, which distinguishes members of the genus.[4]
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.[5] The lineages of the California and Japanese sea lion appear to have split off 2.2 million years ago during the Pliocene.[6] The California sea lion differs from the Galapagos sea lion in its greater sexual dimorphism.[4] The Steller sea lion is the closest extant relative of the Zalophus sea lions, being a sister taxon.[7]
Being sexually dimorphic, California sea lions differ in size, shape, and coloration between the sexes. Males can grow up to 2.5–2.7 m (8.2–8.9 ft) long and weigh up to 523 kg (1,153 lb), while females are typically around 2.1 m (6.9 ft) and weigh up to 100 kg (220 lb).[8][4] Females and juveniles have a tawny brown pelage,[4] although they may be temporarily light gray or silver after molting.[9] The pelage of adult males can be anywhere from light brown to black, but is typically dark brown.[4] The face of adult males may also be light tan in some areas. Pups have a black or dark brown pelage at birth.[9] Although the species has a slender build, adult males have robust necks, chests, and shoulders.[9] Adult males also have a protruding crest which gives them a "high, domed forehead";[10] it is tufted with white hairs.[4] They also have manes, which are less developed than those of adult male South American and Steller sea lions.[10] Both sexes have long, narrow muzzles.[9]
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.[11] The flexibility of its spine allows the California 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.[12] When moving on land, the California 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.[13] California sea lions may travel at speeds of around 10.8 km/h (6.7 mph),[14] 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.[15]
California 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.[16] Sea lions have fairly acute underwater hearing, with a hearing range of 0.4–32 kHz.[17] California 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.[18]
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.[7] 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.[2] 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 California sea lions at the deep waters of the central bay has not been analyzed.[7]
Vagrants can reach the north-western Pacific such as on the Commander Islands.[19] Although several otariinae have been recorded around the Japanese archipelago in recent years, their exact origins are unclear.[20]
During the breeding season, California 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.[9] 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.[21] In 2004, a healthy California 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.[22]
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.[23] They mostly forage near mainland coastlines, the continental shelf, and seamounts. They may also search along the ocean bottom.[9] 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.[24] California sea lions sometimes follow dolphins and exploit their hunting efforts.[4] Adult females feed between 10–100 km (6.2–62.1 mi) from shore.[14] Adult males may forage as far as 450 km (280 mi) from shore when water temperatures rise.[25] 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.
California sea lions are preyed on by orcas and large sharks. At Monterey Bay, California sea lions appear to be the more common food items for transient mammal-eating orcas pods.[26] The California sea lions may respond to the dorsal fin of a killer whale and remain vigilant, even when encountering resident fish-eating pods.[27] California sea lions are also common prey for great white sharks. They have been found with scars made by attacks from both great white sharks and shortfin mako sharks. Sharks attack California sea lions by ambushing them while they are resting at the surface.[28] California sea lions that are attacked in the hindquarters are more likely to survive and make it to the shore.[29]
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 California 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.[30] California sea lions that fail to establish a territory are driven out to sea or gather at a nearby beach.[4]
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.[4] 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.[31] They avoid males that are too aggressive or energetic. Males are usually unable to prevent females from leaving their territories,[4] particularly in water.[32] 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.[32]
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.[32] 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.[9] 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.[33] Older pups may sometimes join their mothers during their foraging trips.[9] 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.[34] Pups are weaned by a year but can continue to suckle for another year.[4]
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. California 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.[35]
Female California 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 California 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.[35] California sea lions can produce vocalizations underwater. These include "whinny" sounds, barks, buzzings, and clicks.[36]
Outside the breeding season, males migrate to the northern ends of the species range to feed, while females forage near the breeding rookeries.[4] California 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. California 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. California sea lions in the Gulf of California do not migrate; they stay in the Gulf of California year-round.[32]
Marine biologist Ronald J. Schusterman and his research associates have studied the California sea lions' cognitive ability. They have discovered that California 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.[37] California sea lions have demonstrated the ability to understand simple syntax and commands when taught an artificial sign language. However, California sea lions rarely used the signs semantically or logically.[38] In 2011, a California sea lion named Ronan was recorded bobbing her head in synchronization to musical rhythms.[39] This "rhythmic entrainment" was previously seen only in humans, parrots and other birds possessing vocal mimicry.[40]
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 California sea lion so it may accidentally balance it or hold the ball on its nose, thereby gaining an understanding of what to do. A California 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.[34] Some organizations, such as the Humane Society of the United States and World Animal Protection, object to using California 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.[41]
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 California sea lions can do this in seconds, before the enemy realizes what happened.[42] Organizations like PETA believe that such operations put the animals in danger.[43] However, the Navy insists that California sea lions are removed once their mission is complete.[44]
The IUCN lists the California sea lion as Least Concern due to "its large and increasing population size."[2] 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.[7] Off the Pacific coast of the United States, California sea lions are so numerous that they are close to carrying capacity, while the Gulf of California population declined by 20% by 2008. California sea lions may be killed when in conflict with fishermen, by poaching, and by entanglements in human-made garbage. They are also threatened by pollutants like DDT and PCB which accumulate in the marine food chain.[2]
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.[45] Applications have been granted for removal of several individual California sea lions at Ballard Locks[46] and at the Bonneville Dam, where up to 92 California sea lions can be killed each year for a 5-year period.[47] Wildlife officials have unsuccessfully attempted to ward off the sea lions using bombs, rubber bullets and bean bags.[48] Efforts to chase sea lions away from the area have also proven ineffective.[49] Critics have objected to the killing of the California 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.[50]
These animals exploit more human-made environments like docks for haul-out sites. Many docks are not designed to withstand the weight of several resting California 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.[51][52]
In January and February 2015, 1450 malnourished or sick California 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 California sea lion pup diet during nursery season.[53] This caused many California sea lion pups to starve, while others died when they took to open waters in search of food at too early an age.[54] 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.[55]
In November 2018, the State of Oregon obtained a permit to kill 93 California sea lions per year below Willamette Falls. Under a similar program, Oregon and Washington had killed over 150 California sea lions on the Columbia River by January 2019.[56][57]
The California sea lion (Zalophus californianus) is a coastal eared seal native to western North America. It is one of six species of sea lions. 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 a protruding sagittal crest. They mainly haul-out on sandy or rocky beaches, but they also frequent manmade environments such as marinas and wharves. California sea lions feed on a number of species of fish and squid, and are preyed on by orcas 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. California sea lions communicate with numerous vocalizations, notably with barks and mother-pup contact calls. Outside their breeding season, California sea lions spend much of their time at sea, but they come to shore to molt.
California 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 California sea lions.
