Sea lion

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Sea lion
Temporal range: Late Oligocene-Holocene
California sea lion in La Jolla (70568).jpg
California sea lion (Zalophus californianus)
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Otariidae
Gray 1825


Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short, thick hair, and a big chest and belly. Together with the fur seals, they comprise the family Otariidae, eared seals, which contains six extant and one extinct species (the Japanese sea lion) in five genera. Their range extends from the subarctic to tropical waters of the global ocean in both the Northern and Southern Hemispheres, with the notable exception of the northern Atlantic Ocean. [1] They have an average lifespan of 20–30 years. A male California sea lion weighs on average about 300 kg (660 lb) and is about 2.4 m (8 ft) long, while the female sea lion weighs 100 kg (220 lb) and is 1.8 m (6 ft) long. The largest sea lion is Steller's sea lion, which can weigh 1,000 kg (2,200 lb) and grow to a length of 3.0 m (10 ft). Sea lions consume large quantities of food at a time and are known to eat about 5–8% of their body weight (about 6.8–15.9 kg (15–35 lb)) at a single feeding. Sea lions can go around 16 knots (30 km/h; 18 mph) in water and at their fastest they can go up to 30 knots (56 km/h; 35 mph). [2] Three species, the Australian sea lion, the Galápagos sea lion and the New Zealand sea lion are listed as Endangered.[ citation needed ]

Pinniped Infraorder of mammals

Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic marine mammals. They comprise the extant families Odobenidae, Otariidae, and Phocidae. There are 33 extant species of pinnipeds, and more than 50 extinct species have been described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage. Pinnipeds belong to the order Carnivora and their closest living relatives are believed to be bears and the superfamily of musteloids, having diverged about 50 million years ago.

Fur seal subfamily of mammals

Fur seals are any of nine species of pinnipeds belonging to the subfamily Arctocephalinae in the family Otariidae. They are much more closely related to sea lions than true seals, and share with them external ears (pinnae), relatively long and muscular foreflippers, and the ability to walk on all fours. They are marked by their dense underfur, which made them a long-time object of commercial hunting. Eight species belong to the genus Arctocephalus and are found primarily in the Southern Hemisphere, while a ninth species also sometimes called fur seal, the northern fur seal, belongs to a different genus and inhabits the North Pacific.

Eared seal family of mammals

An eared seal or otariid or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans and the southern Indian and Atlantic Oceans. They are conspicuously absent in the north Atlantic.



Steller sea lions haul out on a rock off the coast of Raspberry Island (Alaska). Alaska 2007 056.jpg
Steller sea lions haul out on a rock off the coast of Raspberry Island (Alaska).

Sea lions are related to walruses and seals. Together with the fur seals, they constitute the family Otariidae, collectively known as eared seals. Until recently, sea lions were grouped under a single subfamily called Otariinae, whereas fur seals were grouped in the subfamily Arcocephalinae. This division was based on the most prominent common feature shared by the fur seals and absent in the sea lions, namely the dense underfur characteristic of the former. Recent genetic evidence, suggests Callorhinus, the genus of the northern fur seal, is more closely related to some sea lion species than to the other fur seal genus, Arctocephalus. [3] Therefore, the fur seal/sea lion subfamily distinction has been eliminated from many taxonomies.

Northern fur seal eared seal

The northern fur seal is an eared seal found along the north Pacific Ocean, the Bering Sea, and the Sea of Okhotsk. It is the largest member of the fur seal subfamily (Arctocephalinae) and the only living species in the genus Callorhinus. A single fossil species, Callorhinus gilmorei, is known from the Pliocene of Japan and western North America.

Nonetheless, all fur seals have certain features in common: the fur, generally smaller sizes, farther and longer foraging trips, smaller and more abundant prey items, and greater sexual dimorphism. All sea lions have certain features in common, in particular their coarse, short fur, greater bulk, and larger prey than fur seals. For these reasons, the distinction remains useful. The family Otariidae (Order Carnivora) contains the 14 extant species of fur seals and sea lions. Traditional classification of the family into the subfamilies Arctocephalinae (fur seals) and Otariinae (sea lions) is not supported, with the fur seal Callorhinus ursinus having a basal relationship relative to the rest of the family. [4] This is consistent with the fossil record which suggests that this genus diverged from the line leading to the remaining fur seals and sea lions about 6 million years ago (mya). Similar genetic divergences between the sea lion clades as well as between the major Arctocephalus fur seal clades, suggest that these groups underwent periods of rapid radiation at about the time they diverged from each other. The phylogenetic relationships within the family and the genetic distances among some taxa highlight inconsistencies in the current taxonomic classification of the family. [4]

Sexual dimorphism condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs

Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. The condition occurs in many animals and some plants. Differences may include secondary sex characteristics, size, weight, color, markings, and may also include behavioral and cognitive differences. These differences may be subtle or exaggerated, and may be subjected to sexual selection. The opposite of dimorphism is monomorphism.

Arctocephalus is characterized by ancestral character states such as dense underfur and the presence of double rooted cheek teeth and is thus thought to represent the most "primitive" line. It was from this basal line that both the sea lions and the remaining fur seal genus, Callorhinus, are thought to have diverged. The fossil record from the western coast of North America presents evidence for the divergence of Callorhinus about 6 mya, whereas fossils in both California and Japan suggest that sea lions did not diverge until years later. [4]

Caniformia suborder of mammals

Caniformia, or Canoidea, is a suborder within the order Carnivora. They typically possess a long snout and nonretractile claws. The Pinnipedia are also assigned to this group. The center of diversification for Caniformia is North America and northern Eurasia. This contrasts with the feliforms, the center of diversification of which was in Africa and southern Asia.

<i>Arctocephalus</i> genus of mammals

The genus Arctocephalus consists of fur seals. Arctocephalus translates to "bear head."

Australian sea lion species of mammal

The Australian sea lion, also known as the Australian sea-lion or Australian sealion, is a species of sea lion that is the only endemic pinniped in Australia. It is currently monotypic in the genus Neophoca, with the extinct Pleistocene New Zealand sea lion Neophoca palatina the only known congener. These sea lions are sparsely distributed through Houtman Arbrolhos Islands in Western Australia and The Pages Islands in southern Australia. With a population estimated at around 14,730 animals, the Wildlife Conservation Act of Western Australia (1950) has listed them as “in need of special protection”. Their Conservation status is listed as endangered. These pinnipeds are specifically known for their abnormal breeding cycles, which are varied between a 5-month breeding cycle and a 17- to 18-month aseasonal breeding cycle, compared to other pinnipeds which fit into a 12-month reproductive cycle. Females are either silver or fawn with a cream underbelly and males are dark chocolate brown with a yellow mane and are bigger than the females.


Diving adaptations

Sea lion heart. Sea lion heart.jpg
Sea lion heart.

There are many components that make up sea lion physiology and these processes control aspects of their behavior. Physiology dictates thermoregulation, osmoregulation, reproduction, metabolic rate, and many other aspects on sea lion ecology including but not limited to their ability to dive to great depths. The sea lions' bodies control heart rate, gas exchange, digestion rate, and blood flow to allow individuals to dive for a long period of time and prevent side-effects of high pressure at depth.

The high pressures associated with deep dives cause gases such as nitrogen to build up in tissues which are then released upon surfacing, possibly causing death. One of the ways sea lions deal with the extreme pressures is by limiting the amount of gas exchange that occurs when diving. The sea lion allows the alveoli to be compressed by the increasing water pressure thus forcing the surface air into cartilage lined airway just before the gas exchange surface. [5] This process prevents any further oxygen exchange to the blood for muscles, requiring all muscles to be loaded with enough oxygen to last the duration of the dive. However, this shunt reduces the amount of compressed gases from entering tissues therefore reducing the risk of decompression sickness. [5] The collapse of alveoli does not allow for any oxygen storage in the lungs however, this means that sea lions must mitigate oxygen use in order to extend their dives. Oxygen availability is prolonged by the physiological control of heart rate in the sea lions. By reducing heart rate to well below surface rates, oxygen is saved by reducing gas exchange as well as reducing the energy required for a high heart rate. [6] Bradycardia is a control mechanism to allow a switch from pulmonary oxygen to oxygen stored in the muscles which is needed when the sea lions are diving to depth. [6] Another way sea lions mitigate the oxygen obtained at the surface in dives is to reduce digestion rate. Digestion requires metabolic activity and therefore energy and oxygen are consumed during this process, however sea lions can limit digestion rate and decrease it by at least 54%. [7] This reduction in digestion results in a proportional reduction in oxygen use in the stomach and therefore a correlated oxygen supply for diving. Digestion rate in these sea lions increase back to normal rates immediately upon resurfacing. [7] Oxygen depletion limits dive duration, but carbon dioxide (CO2) build up also plays a role in the dive capabilities of many marine mammals. After a sea lion returns from a long dive, CO2 is not expired as fast as oxygen is replenished in the blood, due to the unloading complications with CO2. However, having more than normal levels of CO2 in the blood does not seem to adversely affect dive behavior. [8] Compared to terrestrial mammals, sea lions have a higher tolerance to storing CO2 which is what normally tells mammals that they need to breathe. [8] This ability to ignore a response to CO2 is likely brought on by increase carotid bodies which are sensor for oxygen levels which let the animal know its available oxygen supply. [8] Yet, the sea lions cannot avoid the effects of gradual CO2 build up which eventually causes the sea lions to spend more time at the surface after multiple repeated dives to allow for enough built up CO2 to be expired. [8]

Parasites and diseases

Behavioural and environmental correlates of Philophthalmus zalophi, a foot parasite. And the infection has impacted the survival of juvenile Galapagos sea lions (Zalophus wollebaeki). [9] This infection leads to diseases that are connected to global warming. The number of infectious stages of different parasites species has a strong correlation with temperature change, therefore it is essential to consider the correlation between the increasing number of parasitic infections and climate changes. To test this proposed theory researchers used Galapagos sea lions because they are endemic to the Galapagos islands. [9] The Galapagos Islands goes through seasonal changes in sea surface temperatures, which consist of high temperatures from the beginning of January through the month of May and lower temperatures throughout the rest of the year. Parasites surfaced in large numbers when the sea temperature was at its highest. Furthermore, data was collected by capturing sea lions in order to measure and determine their growth rates. Their growth rates were noted along with the citings of parasites which were found under the eyelid. The shocking results were that sea lions are affected the parasites from the early ages of 3 weeks old up until the age of 4 to 8 months. [9] The parasites found in the eye fluke did serious damage to the eye. From the data collected, 21 of the 91 survived; with a total of 70 deaths in just a span of two years. [9] The parasites are attacking the pups at such young ages; thus causing the pups to not reach the age of reproduction. The death rates of the pups is surpassing the fertility rate by far. Since most pups are unable to reach the age of reproduction, the population is not growing fast enough to keep the species out of endangerment. The pups who do survive must pass their strong genes down to make sure their young survive and the generation that follows. Other parasites, like Anisakis and heartworm can also infect sea lions.

Along with Galapagos islands, sea lions (Zalophus wollebaeki) being affected are the Australian sea lions (Neophoca cinerea). [10] The same method was used for the sea pups on the galapagos island, but in addition, the researchers in Australia took blood samples. The pups in Australia were being affected by hookworms, but they were also coming out in large numbers with warmer temperatures. [10] Sea pups in New Zealand (Phocarctos hookeri) were also affected really early ages by hookworms (Uncinaria). The difference is that in New Zealand researchers took the necessary steps and began treatment. [11] The treatment seemed to be effective on the pups who have taken it. They found no traces of this infection afterwards. However, the percentage of pups who do have it is still relatively high at about 75%. [11] Those pups who were treated had much better growth rates than those who did not. Overall parasites and hookworms are killing off enough pups to place them in endangerment. Parasites affect sea pups in various areas of the world. Reproductive success reduces immensely, survival methods, changes in health and growth have also been affected.

Gene expressions and diet

Diet is an important factor in the well-being of any animal’s life. Gene expressions are being used more often to detect the physiological responses to nutrition, as well as other stressors. In a study done with four Steller sea lions (Eumetopias jubatus), three of the four sea lions underwent a 70-day trial which consisted of unrestricted food intake, acute nutritional stress, and chronic nutritional stress. [12] The results of this study showed that the sea lions with nutritional stress down-regulated some cellular processes within their immune response and oxidative stress. [12] Sea lions get affected greatly due to environmental changes because of the dependency they have on marine resources for feeding. [12] A reduced food supply leads to population decline. Compared to many other factors that contribute to an endangered species, nutritional stress is the most proximate cause to population decline. [12]

The New Zealand sea lion has the largest population, therefore no diet studies had ever been conducted. However, when a study was finally conducted the location and climate change effects it had on diet were discovered. [13] North to south composition of a sea lion's diet showed that the temperature gradients were a key factor in the prey mix that was available for the NZ sea lions. [13]

Geographic variation

Geographic variation for sea lions have been determined by the observations of skulls of several Otariidae species; a general change in size corresponds with a change in latitude and primary productivity. Skulls of Australian sea lions from Western Australia were generally smaller in length whereas the largest skulls are from cool temperate localities. Otariidae are in the process of species divergence, much of which may be driven by local factors, particularly latitude and resources. [14] Populations of a given species tend to be smaller in the tropics, increase in size with increasing latitude, and reach a maximum in sub-polar regions. In a cool climate and cold waters there should be a selective advantage in the relative reduction of body surface area resulting from increased size, since the metabolic rate is related more closely to body surface area than to body weight. [14]

Breeding and population

Breeding methods and habits

Two sea lions on the beach of Otago Peninsula, New Zealand Two sea lions on the beach of Otago Peninsula.jpg
Two sea lions on the beach of Otago Peninsula, New Zealand

Sea lions, with three groups of pinnipeds, have multiple breeding methods and habits over their families but they remain relatively universal. Otariids, or eared sea lions, raise their young, mate, and rest in more earthly land or ice habitats. Their abundance and haul-out behavior have a direct effect on their on land breeding activity. Their seasonal abundance trend correlates with their breeding period between the austral summer of January to March. Their rookeries populate with newborn pups as well as male and female otariids that remain to defend their territories. At the end of the breeding period males disseminate for food and rest while females remain for nurturing. Other points in the year consist of a mix of ages and genders in the rookeries with haul-out patterns varying monthly. [15]

Steller sea lions, living an average of 15 to 20 years, begin their breeding season when adult males establish territories along the rookeries in early May. Male sea lions reach sexual maturity from ages 5 to 7 and don’t become territorial until around 9 to 13 years of age. The females arrive in late May bringing in an increase of territorial defense through fighting and boundary displays. After a week births consist most usually of one pup with a perinatal period of 3 to 13 days.

Steller sea lions have exhibited multiple competitive strategies for reproductive success. Sea lion mating is often polygamous as males usually mate with different females to increase fitness and success, leaving some males to not find a mate at all. Polygamous males rarely provide parental care towards the pup. Strategies used to monopolize females include the resource-defense polygyny, or occupying important female resources. This involves occupying and defending a territory with resources or features attractive to females during sexually receptive periods. Some of these factors may include pupping habitat and access to water. Other techniques include potentially limiting access of other males to females. [16]


Otaria flavescens (South American sea lion) lives along the Chilean coast with a population estimate of 165,000. According to the most recent surveys in northern and southern Chile the sealing period of the middle twentieth century that left a significant decline in sea lion population is recovering. The recovery is associated with less hunting, otariids rapid population growth, legislation on nature reserves, and new food resources. Haul-out patterns change the abundance of sea lions at particular times of the day, month, and year. Patterns in migration relate to temperature, solar radiation, and prey and water resources. Studies of South American sea lions and other otariids document maximum population on land during early afternoon, potentially due to haul-out during high air temperatures. Adult and subadult males do not show clear annual patterns, maximum abundance being found from October to January. Females and their pups hauled-out during austral winter months of June to September. [17]

Interactions with humans

Sea lions entertaining a crowd in Central Park Zoo. Sea lions entertaining crowd in Central Park Zoo, New York City 2.jpg
Sea lions entertaining a crowd in Central Park Zoo.

South American sea lions have been greatly impacted by human exploitation. During the late Holocene period to the middle of the twentieth century, hunter gatherers along the Beagle Channel and northern Patagonia had greatly reduced the number of sea lions due to their exploiting and hunting of the species and of the species’ environment. [18] Although sealing has been put to a halt in many countries, such as Uruguay, the sea lion population continues to decline because of the drastic effects humans have on their ecosystems. [18] As a result, South American sea lions have been foraging at higher tropical latitudes than they did prior to human exploitation. [18] Fishermen play a key role in the endangerment of sea lions. Sea lions rely on fish, like pollock, as a food source and have to compete with fishermen for it. [19] When fishermen are successful at their job, they greatly reduce the sea lion’s food source, which in turn endangers the species. [19] Also, human presence and human recreational activities can cause sea lions to engage in violent and aggressive actions. [20] When humans come closer than 15 meters of a sea lion, the sea lions' vigilance increases because of the disturbance of humans. [20] These disturbances can potentially cause sea lions to have psychological stress responses that cause the sea lions to retreat, sometimes even abandon their locations, and decreases the amount of time sea lions spend hauling out. [20]

Hundreds of California sea lions congregating at Pier 39, San Francisco Cal Sea Lions on Pier 39.JPG
Hundreds of California sea lions congregating at Pier 39, San Francisco

Sea lion attacks on humans are rare, but when humans come within approximately 2.5 meters, it can be very unsafe. [20] In a highly unusual attack in 2007 in Western Australia, a sea lion leapt from the water and seriously mauled a 13-year-old girl surfing behind a speedboat. The sea lion appeared to be preparing for a second attack when the girl was rescued. An Australian marine biologist suggested that the sea lion may have viewed the girl "like a rag doll toy" to be played with. [21] [22] [23] In San Francisco, where an increasingly large population of California sea lions crowds docks along San Francisco Bay, incidents have been reported in recent years of swimmers being bitten on the legs by large, aggressive males, possibly as territorial acts. [24] [25] In April 2015, a sea lion attacked a 62-year-old man who was boating with his wife in San Diego. The attack left the man with a punctured bone. [26] In May 2017, a sea lion dragged a small girl into the water by her dress. She was sitting on a pier side in British Columbia while tourists were illegally feeding the sea lions. [27] She was pulled out of the water with minor injuries and received antibiotic prophylactic treatment for seal finger infection from the superficial bite injury. [28] [29]

Sea lions have also been a focus of tourism in Australia and New Zealand. [20] One of the main sites to view sea lions is in the Carnac Island Nature Reserve near Perth in Western Australia. This tourist site receives over 100,000 visitors, many of whom are recreational boaters and tourists, who can watch the male sea lions haul out on to the shore. [20] They have sometimes been called "the unofficial welcoming committee of the Galápagos Islands". [30]

Zalophus californianus at Moss Landing 3.jpg GiGi sea lion 1984.jpg Sea lion head.jpg Sea Lion Lounging.JPG
A gathering of more than 40 sea lions off the coast of CaliforniaA military sea lion on board a U.S. Navy shipA sea lion at the Memphis Zoo A sea lion pup sleeping at Pantai Inn
Sea lion head by the ocean.jpg Sealion052006.JPG Sea lion chillin'.jpg Sea lions chillin'.jpg
A sea lion in Malibu, CaliforniaSea Lion at Monterey BreakwaterA sea lion sleeps in the Ballestas Islands, PeruA group of sea lions rest in the Ballestas Islands, Peru

See also

Related Research Articles

Earless seal family of mammals

The earless seals, phocids or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae. They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

Steller sea lion species of mammal

The Steller sea lion, also known as the northern sea lion and Steller's sea lion, is a near-threatened species of sea lion in the northern Pacific. It is the sole member of the genus Eumetopias and the largest of the eared seals (Otariidae) and is also the largest species of sea lion. Among pinnipeds, it is inferior in size only to the walrus and the two species of elephant seals. The species is named for the naturalist Georg Wilhelm Steller, who first described them in 1741. The Steller sea lion has attracted considerable attention in recent decades, owing to significant and largely unexplained declines in their numbers over an extensive portion of their northern range in Alaska.

Juan Fernández fur seal species of mammal

The Juan Fernández fur seal is the second smallest of the fur seals, second only to the Galápagos fur seal. They are found only on the Pacific Coast of South America, more specifically on the Juan Fernández Islands and the Desventuradas Islands. There is still much that is unknown about this species. Scientists still do not know the average life span of this species, or the diet and behavior of males apart from the breeding season.

Galápagos fur seal species of mammal

The Galápagos fur seal breeds on the Galápagos Islands in the eastern Pacific, west of mainland Ecuador.

Brown fur seal species of fur seal

The brown fur seal, also known as the Cape fur seal, South African fur seal, and Australian fur seal, is a species of fur seal.

<i>Neophoca</i> genus of mammals

Neophoca is a genus of the family Otariidae of order Carnivora. It is combined by some taxonomists with the genus Phocarctos, the (extant) New Zealand sea lion. Only one species survives:

<i>Arctocephalus forsteri</i> species of mammal

Arctocephalus forsteri, the Australasian fur seal, South Australian fur seal, New Zealand fur seal, Antipodean fur seal, or long-nosed fur seal, is a species of fur seal found mainly around southern Australia and New Zealand. The name New Zealand fur seal is used by English speakers in New Zealand; kekeno is used in the Māori language. As of 2014, the common name long-nosed fur seal has been proposed for the population of seals inhabiting Australia.

Galápagos sea lion species of mammal

The Galápagos sea lion is a species of sea lion that exclusively breeds on the Galápagos Islands and – in smaller numbers – on Isla de la Plata (Ecuador). Being fairly social, and one of the most numerous species in the Galápagos archipelago, they are often spotted sun-bathing on sandy shores or rock groups or gliding gracefully through the surf. Their loud bark, playful nature, and graceful agility in water make them the "welcoming party" of the islands. They are the smallest sea lions.


Hauling-out is a behaviour associated with pinnipeds temporarily leaving the water. Hauling-out typically occurs between periods of foraging activity. Rather than remain in the water, pinnipeds haul-out onto land or sea-ice for reasons such as reproduction and rest. Hauling-out is necessary in seals for mating and giving birth. Other benefits of hauling-out may include predator avoidance, thermoregulation, social activity, parasite reduction and rest.

Pleistocene New Zealand sea lion is an extinct species of pinniped known from a nearly-complete adult male skull found at Ohope Beach on the North Island in 1937. It was found in a stratum from the late Castlecliffian stage, suggesting an approximate age of 400,000 years. It was not recognised as representing a new species until 1983, distinguishable from the extant Australian sea lion and New Zealand sea lion by the short palate, lack of processes on the ethmoid bulla and the very wide basiocciptal. A more advanced morphometric analysis in 2016 strongly confirmed that the skull represented a distinct species, closely related to the Australian sea lion. Paleoclimate reconstructions suggest that N. palatina was more tolerant of cold water temperatures than N. cinerea, the only other known member of the genus.


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Further reading