Steller sea lion

The Steller sea lion (Eumetopias jubatus), also known as the northern sea lion and Steller's sea lion, is a near-threatened species of sea lions 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 sea lion. Among pinnipeds, it is inferior in size only to the walrus and the two 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, unexplained declines in their numbers over a large portion of their range in Alaska.

Steller sea lion
Steller sea lion adult male, female and pup on Yamsky Islands in the northeast Sea of Okhotsk
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Clade: Pinnipedia
Family: Otariidae
Genus: Eumetopias
Gill, 1866
E. jubatus
Binomial name
Eumetopias jubatus
Schreber, 1776
Eumetopias jubatus distribution2
Range of Steller sea lions (purple = overall range, red = breeding rookeries)


Steller sea lion skull

Adult animals are lighter in colour than most sea lions, ranging from pale yellow to tawny and occasionally reddish. Steller sea lion pups are born almost black, weighing around 23 kg (51 lb), and remain dark for several months. Females and males both grow rapidly until the fifth year, after which female growth slows considerably. Adult females measure 2.3–2.9 m (7.5–9.5 ft) in length, with an average of 2.5 m (8.2 ft), and weigh 240–350 kg (530–770 lb), with an average of 263 kg (580 lb).[2][3] Males continue to grow until their secondary sexual traits appear in their fifth to eighth year. Males are slightly longer than the females; they grow to about 2.82–3.25 m (9.3–10.7 ft) long, with an average of 3 m (9.8 ft).[4] Males have much wider chests, necks, and general forebody structure and weigh 450–1,120 kg (990–2,470 lb), with an average of 544 kg (1,199 lb).[5][6][7] Males are further distinguished from females by broader, higher foreheads, flatter snouts, and a thick mane of coarse hair[8] around their large necks. Indeed, their Latin name translates roughly as "maned one with the broad forehead".


The range of the Steller sea lion extends from the Kuril Islands and the Sea of Okhotsk in Russia to the Gulf of Alaska in the north, and south to Año Nuevo Island off central California. They formerly bred as far south as the Channel Islands, but have not been observed there since the 1980s. Based on genetic anаlyses and local migration patterns, the global Steller sea lion population has traditionally been divided into an eastern and western stock at 144°W longitude, roughly through the middle of the Gulf of Alaska.[9][10] Recent evidence suggests the sea lions in Russia in the Sea of Okhotsk and the Kuril Islands comprise a third Asian stock, while the sea lions on the eastern seaboard of Kamchatka and the Commander Islands belong to the western stock.

Steller sealions bc 1
Steller sea lions congregate on rocks in the Gulf Islands of British Columbia

In the summer, Steller sea lions tend to shift their range somewhat southward. Thus, though no reproductive rookeries are in Japan, several consistent haulouts are found around Hokkaidō in the winter and spring. Vagrants have been spotted in the Yellow Sea and Bohai Gulf and along the coast of Korea and China.[1][11]



Steller sea lions tend to live in the coastal waters of the subarctic because of the cooler temperate climate of the area.[12] Like all otariids, Steller sea lions are amphibious and spend some time in water and some on land.[13] Typically, Stellar sea lions spend their time in the water feeding but haul-out onto land to reproduce, raise their pups, molt, and rest.[14] Steller sea lions usually congregate on isolated islands because they are the ideal terrestrial habitat. These isolated islands are preferred by Stellar sea lions because they can avoid predation from terrestrial predators, easily thermoregulate (cooling winds), and access offshore prey more easily.[13] Some haul-out sites, known as rookeries, are commonly used for reproduction while other haul-out sites, nonbreeding sites, are used for other purposes like molting.[15] However, biotic and abiotic factors can influence the amount of time that Steller sea lions spend on land. Haul-out sites and haul-out abundance of the Steller sea lion is determined by prey availability, predator abundance, tide levels, weather, etc.[15]


Sea lion and Sturgeon
Steller sea lion with white sturgeon

Steller sea lions are skilled and opportunistic marine predators, feeding on a wide range of fish and cephalopod species. Important diet components include walleye pollock,[16][17] Atka mackerel,[16] halibut,[17] herring, capelin,[18] flatfish[18][19] Pacific cod,[16][17] rockfish,[18][19] sculpins,[18] Salmon, Sand lance, cephalopods like squid and octopus.[16] They seem to prefer schooling fish and remain primarily between intertidal zones and continental shelves. They usually aggregate in groups of 1-12, and aggregate in areas of prey abundance. They are known to aggregate near fishing vessels, preying on by catch discards. Most of the data on their foraging comes from data collected off the coast of Alaska, and their foraging behaviors globally are unknown. In addition to their primary marine environment, they are also known to enter estuarine environments and feed on some brackish-water fish such as sturgeon. Very occasionally, they have been known to prey on northern fur seals, harbor seals, and sea otter pups. It has been recorded that their prey variety has broadened overtime.[1] Their diet composition varies seasonally and geographically. They are opportunistic predators, capitalizing on the most abundant prey species.[20]


Steller Sea Lions are top-level carnivores, but are susceptible to predation primarily by killer whales. Shark species are also a possible predator, sleeper sharks preying on juvenile sea lions, and also great white sharks.[1]

Behavior and life history


2008 Juneau Steller Sea Lion Haram (8101629225)
Adult bull, females, and pups near Juneau, Alaska

Reproductively mature male sea lions aggregate in May on traditional, well-defined reproductive rookeries,[21][22] usually on beaches on isolated islands. The larger, older males establish and defend distinct territories on the rookery.[21][22] A week or so later, adult females arrive, accompanied occasionally by sexually immature offspring, and form fluid aggregations throughout the rookery. Like all other otariids, Steller sea lions are polygynous. However, unlike some other species, they do not coerce individual females into harems, but control spatial territories among which females freely move about.[21] Steller sea lions have used aquatic, semiaquatic, and terrestrial territories. Males with semiaquatic territories have the most success in defending them.[22] The boundaries are defined by natural features, such as rocks, faults, or ridges in rocks, and territories can remain stable for 60 days.[21] Though Steller sea lion males are generally tolerant of pups, one male filmed on Medny Island in Russia was documented killing and eating several pups in a first-ever recorded incident of cannibalism. Though researchers are uncertain as to the motives or reasons behind said attacks, it is suggested that the bull involved may have an abnormal personality akin to being psychotic.[23]

Steller sea lion pup (Kuril Islands, Russia)

Pregnant females give birth soon after arriving on a rookery, and copulation generally occurs one to two weeks after giving birth,[21][22] but the fertilized egg does not become implanted in the uterus until the fall. A fertilized egg may remain inside a female for up to three months before being implanted and beginning to form into a blastocyst.[24] Twins are rare.[25] After a week or so of nursing without leaving the rookery, females begin to take progressively longer and more frequent foraging trips, leaving their pups behind, until at some point in late summer the mother and pup both leave the rookery. This behavior is called the maternal attendance pattern and is common in otariids. As pups get older the amount of time spent by females foraging out at sea increases.This continues until pups obtain the ideal body weight and energy reserves in order to eat on their own. A study conducted by the University of California, Santa Cruz found that on average male pups consume more milk than females; this may be due to the differences in sexual dimorphism common to otariids.[26] Reproductive males fast throughout the reproductive season,[27] often without entering the water once from mid May until August, when the structure of the reproductive rookeries begins to fall apart and most animals leave for the open seas and disperse throughout their range.

The age at weaning is highly variable; pups may remain with their mothers for as long as four years. Incidents of mothers feeding daughters that are simultaneously feeding their own newborn pups have been documented, an extremely rare occurrence among mammals. A study done at Ano Nuevo in 1983 found that female attendance and time spent with their pup was shaped by increasing nutritional demands of the pup and the pups suckling efficiency. Females average having 21 hours ashore and 36 hours at sea. As the pups aged, females began to spend more time at sea again. As the pups mature, specifically at the sixth week past parturition, the mother's sea time declines by 30 percent. There is no relationship between the pups activity, or physical excursion to their suckling time, age, or sex. Their suckling time, and age and gender are unrelated to their use of energy. Labeled water studies showed that milk intake of the pup's had a direct relationship to their size. Pups that consumed more milk were heavier than those that didn't. These findings show that the amount of time females spend onshore with their pups is based on their pup's suckling efficiency and nutritional demands, their metabolic needs.[28]

In the past, the low pup production has been tied to an increase in nutritional stress found in females. This was believed to have contributed to the decline in Steller sea lions common to Alaska.[24]

Diving adaptations and behavior

Steller sea lion releasing air underwater

In order to be able to dive for a long period of time, Steller sea lions exhibit apnea, bradycardia, and peripheral vasoconstriction. This allows them to maximize their oxygen stores and efficiently forage during their dives. In addition to those adaptations, their thick blubber layer and outer fur layer keep their body insulated during dives.[29]

Trained Steller sea lions from Vancouver Aquarium were placed in the open ocean research station at the University of British Columbia's Open Water Research Station to study their diving metabolism and behavior.[30] Steller sea lions' dives are more energetically costly if they perform dive bouts. The aerobic diving limit (ADL) of Steller sea lion was observed to be affected by their nutritional state and feeding.[31]


Like most otariids, Steller sea lions are vocal in air. Mature male sea lions have a range of vocalizations as part of their territorial behaviors, including belches, growls, snorts, and hisses that serve as warnings to others. Both males and females also produce underwater noises similar to their above water sounds, described as clicks, barks, and belches.[32] The primary function of their vocalizations is for social behavior. Sonogram readings reported that Steller Sea Lions make discrete, low frequency pulses underwater that resemble the male "belching" territorial noise made in air. These underwater vocalizations have an average of 20-30 pulses per second.[33]

Vocalizations are critical to mother-pup pairs, as the mothers must find their pups in a crowded breeding area when they return from foraging. The mother and pup both use distinctive calls, like names, to help differentiate themselves among the crowd of other sea lions.[34] Their aerial vocalizations have been described as similar to the bleats of sheep, and bellows.

Because Steller sea lions are sexually dimorphic in size, their hearing differs in sensitivity, possibly due to differences in size of the hearing structures. Females have a higher sensitivity than males, perhaps to hear the higher frequency calls of their pups. The Steller sea lion's hearing range also suggests that they are capable of hearing the underwater calls of one of their main predators, the killer whale.[35]

Interactions with humans

Amak Island, Steller's Sea Lion haul out
Steller sea lions haul out on Amak Island

Steller sea lion were hunted for meat and other commodities by prehistoric communities everywhere their range intersected with human communities. Aside from food and clothing, their skin was used to cover baidarkas and kayaks. A subsistence harvest on the order of 300 animals or less continues to this day in some native communities in Alaska.[1]

Historically, the sea lion has had only very slight commercial value. For example, in the 19th century their whiskers sold for a penny apiece for use as tobacco-pipe cleaners.[36]

Steller sea lions are sometimes killed intentionally by fishermen, as they are seen as competitors and a threat to fish stocks.[1] Killing sea lions is strictly prohibited in the U.S.A. and Russia, but in Japan a fixed number are still removed annually, ostensibly to protect their fisheries. In Canada, commercial hunting is prohibited, but limited hunting permits are occasionally granted if local culling is required—for example, nuisance animals destroying fish farms.

In recent years, Steller sea lions have been known to enter the Columbia River estuary and feed on white sturgeon, several salmon species, and rainbow trout, some of which are also listed under the U.S. Endangered Species Act. They enter the Columbia River primarily in the late winter and spring, occasionally going as far upstream as Bonneville Dam.[37] Though not as abundant as the California sea lion, they are still a concern for those agencies charged with managing the fish populations. Since the Steller sea lions are themselves protected under the Marine Mammal Protection Act,[1] managers are compelled to use nonlethal deterrence methods, such as rubber bullets and noisemakers. Deterrence by the public is strictly forbidden.

Recent decline and subsequent recovery

Stellers Sea Lions BC
Steller sea lions near Vancouver Island

While the populations of the eastern and Asian stocks appear stable, the population of the western stock, particularly along the Aleutian Islands, was estimated to have fallen by 70–80% since the 1970s. As a consequence, in 1997 the western stock of Steller sea lions was listed as endangered and the eastern stock was listed as threatened under the United States Endangered Species Act.[38][39] They have since been the object of intense study and the focus of much political and scientific debate in Alaska.

One suspected cause of their precipitous decline was overfishing of Alaska pollock, herring, and other fish stocks in the Gulf of Alaska. This stems largely from the “junk-food hypothesis” representing a shift in their diet from fatty herring and capelin to leaner fare such as pollock and flounder, thereby limiting their ability to consume and store fat.[40] Other hypotheses include increased predation by orcas[41] and sharks,[42] indirect effects of prey species composition shifts due to changes in climate, effects of disease or contaminants, shooting by fishermen, and others. The decline is certainly due to a complex of interrelated factors which have yet to be defined by the research effort.[43][44]

Another possible reason for decline in this species has been tied to the Nutritional Stress Hypothesis. The lack of prey corresponds to the decrease in population. In females specifically, obtaining an insufficient amount of nutrients has resulted in the failure to complete their pregnancies to full term.[45]

In October 2013, the eastern Steller sea lion was taken off the U.S. Endangered Species List after a major population comeback over the past several years.[46]


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Further reading

  • Heptner, V. G.; Nasimovich, A. A; Bannikov, Andrei Grigorevich; Hoffmann, Robert S, Mammals of the Soviet Union, Volume II, part 3. Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation

External links

Adugak Island

Adugak Island (also spelled Adougakh, possibly from Aleut: Adudak) is a small island in the Fox Islands group in the Aleutian Islands of southwestern Alaska. It is about 1.2 miles (2 km) long and is located 5.0 miles (8 km) off the northwest coast of Umnak Island. The island has been protected as a rookery for the endangered Steller sea lion, which has been observed during the winter feeding on the fish that inhabit the water nearby. The island reaches an elevation of about 102 feet (31 m) above sea level and the area around the island is extremely hazardous to ships because of the numerous rocks that lie just below the surface of the water.

Amak Island

Amak Island (Aleut: Amax) is an uninhabited island in Aleutians East Borough, Alaska, United States. The island lies north of the western tip of the Alaska Peninsula, and northwest of the mainland city of Cold Bay. The island's land area is 5.828 square miles (15.09 km2) and its maximum elevation is 1,601 feet (488 m). The island's volcano, Mount Amak, last erupted in 1796.

The local population of the song sparrow was last seen on the island around New Year's Eve, 1980/1981, and has not been seen since; devegetation of the island played a part in its demise. These birds were formerly considered a separate subspecies, Melospiza melodia amaka, but are now considered to fall into the range of variation of the Aleutian song sparrow (M. m. sanaka). Unconfirmed reports from the late 1980s suggest that the island, should habitat quality improve, would in time be recolonized by the species.


Archaeodobenus is an extinct genus of pinniped that lived during the Late Miocene of what is now Japan. It belonged to the Odobenidae family, which is today only represented by the walrus, but was much more diverse in the past, containing at least 16 genera. Unlike the modern walrus, Archaeodobenus did not have tusks but instead had canines of moderate size, and looked more like a sea lion.

The first known specimen was collected in 1977 from the Ichibangawa Formation in Tobetsu Town on the island of Hokkaido. The specimen consists of a partial skull, vertebrae, and limb bones, and was made the holotype specimen of the new genus and species A. akamatsui by the Japanese palaeontologists Yoshihiro Tanaka and Naoki Kohno in 2015. The generic name consists of archaio, the Greek word for ancient, and the generic name of the walrus, Odobenus; in full, "ancient walrus". The specific name honours Morio Akamatsu, a curator of the Hokkaido Museum.The diversity of odobenids increased during the Late Miocene and Pliocene (about 12.5 million to 10.5 million years ago), perhaps linked to marine regression and transgression, which could have geographically isolated their ancestors. Archaeodobenus was the contemporary of the odobenid Pseudotaria from the same formation, which it may have diverged from in the western North Pacific during the Late Miocene. Archaeodobenus appears to have been closer related to later odobenids such as Imagotaria, Pontolis, the subfamily Odobeninae, whereas Pseudotaria seems to have been more basal.The holotype specimen appears to have been a young adult male of about 3 metres (10 ft) in length, which would have weighed around 473 kg (1,042 lb). This is intermediate between the size of the Steller sea lion and the South American sea lion. Its canines were 86.3 mm (3.4 in) long, while those of a walrus are up to 1 m (3 ft 3 in) long in comparison. Archaeodobenus can be distinguished from Pseudotaria by features such as the shape and size of the occipital condyle (which connects with the first neck vertebra at the back of the skull), the foramen magnum (the opening through which the spinal chord passes into the cranium), the mastoid process (where various muscles attach to the back of the skull), as well as some features in the postcranial skeleton.

Atka mackerel

The Atka mackerel (Pleurogrammus monopterygius) is a mackerel in the family Hexagrammidae. Atka mackerel are common to the northern Pacific ocean, and are one of only two members of the genus Pleurogrammus - the other being the Arabesque greenling (Pleurogrammus azonus). The Atka mackerel was named for Atka Island (Atx̂ax̂ in Aleut), the largest island of the Andreanof islands, a branch of the Aleutians.

Eared seal

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 (another species became extinct in the 1950s) 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.

The words 'otariid' and 'otary' come from the Greek otarion meaning "little ear", referring to the small but visible external ear flaps (pinnae), which distinguishes them from the phocids.

Forrester Island (Alaska)

Forrester Island is an island in the U.S. state of Alaska. It is located off the coast of the Alaska Panhandle, near its southernmost portion, 20 miles (32 km) west of Dall Island, in the Prince of Wales-Hyder Census Area. The island is 5.2 miles (8.4 km) long and covers an area of 3.97 sq mi (10.29 km2). It is wooded and mountainous, rising 814 feet (248 m) in elevation.

Forrester Island was originally named "Santa Cristina" by Juan Pérez in 1774. In 1775, Francisco Antonio Maurelle labeled the island "San Carlos", and in 1778 William Douglas named it "Douglas Island". Royal Navy officer George Dixon named the island "Forrester Island" in 1787, which was the name adopted by George Vancouver on the Vancouver Expedition in 1793. In 1912, U.S. President William Howard Taft signed a law creating the Forrester Island Refuge, which included Forrester Island, Lowrie Island and Wolf Rock. In 1970, the area was designated the Forrester Island Wilderness.The island hosts rookeries of Steller sea lions. The longest recorded migration of a Steller sea lion was 1,600 miles (2,600 km) between Forrester Island and Cape Newenham in Bristol Bay.

Kasatochi Island

Kasatochi Island (Aleut: Qanan-tanax̂), also known as Kasatochi volcano, is an active stratovolcano and one of the Andreanof Islands subgroup of the Aleutian Islands of southwestern Alaska.

List of largest protected areas

The World Database on Protected Areas (WDPA) is compiled and managed by the World Conservation Monitoring Centre, an executive agency of the United Nations Environment Programme. It uses the IUCN and CBD definitions of protected areas to determine whether a site should be included in the WDPA. The twenty largest protected areas in the October 2017 edition of the WDPA are listed below, in order of size as reported by the relevant data provider. All are marine protected areas except for Northeast Greenland National Park, which is mostly terrestrial but also has a marine component. Protected areas with multiple coterminous or overlapping designations (e.g. Northeast Greenland National Park and the corresponding Biosphere Reserve) are listed only once.

List of marine mammal species

Marine mammals comprise over 130 living and recently extinct species in three taxonomic orders. The Society for Marine Mammalogy, an international scientific society, maintains a list of valid species and subspecies, most recently updated in October 2015. This list follows the Society's taxonomy regarding and subspecies.

Conservation status codes listed follow the IUCN Red List of Threatened Species (v. 2014.3; data current at 19 January 2015) and are clickable to link to IUCN Red List species pages.

List of threatened mammals of the United States

According to the International Union for Conservation of Nature (IUCN), 65 mammal species in the United States are threatened or nearly threatened with extinction. The IUCN has classified each of these species into one of four conservation statuses: near threatened NT, vulnerable VU, endangered EN, and critically endangered CR. Also included in the list are 5 species that became extinct EX since the 1500s.


Lutrogale is a genus of otters, with only one extant species—the smooth-coated otter.

Opisthoteuthis californiana

Opisthoteuthis californiana, also known as the flapjack octopus, is a species of umbrella octopus.


Raikoke (Russian: Райкоке, Japanese: 雷公計島), also spelled Raykoke, is an uninhabited volcanic island near the centre of the Kuril Islands chain in the Sea of Okhotsk in the northwest Pacific Ocean, 16 kilometres (9.9 mi) across Golovnin Strait from Matua. Its name is derived from the Ainu language, from “hellmouth”.

Vesicular exanthema of swine virus

Vesicular exanthema of swine virus (VESV) is a virus which produces a disease in pigs that is clinically indistinguishable from the viruses causing foot-and-mouth disease (FMD) and swine vesicular disease (SVD). VESV affects only pigs and marine mammals. It is not transmissible to humans.

VESV is only a concern among Californian pig-farmers; otherwise, the disease is now, by and large, a historical curiosity. It was globally eradicated in swine in 1959.


Vesivirus is a genus of viruses, in the family Caliciviridae. Swine, sea mammals, and felines serve as natural hosts. There are currently only two species in this genus including the type species Vesicular exanthema of swine virus. Diseases associated with this genus include: respiratory disease, Feline calicivirus (FCV); conjunctivitis, and respiratory disease.

Yam Islands

Not to be confused with Yam Island in Queensland, Australia.The Yam Islands, Yamsky Islands or Yamskiye Islands (Ямские острова; Yamskiye Ostrova), is a small island group located close to the coast in the northern Sea of Okhotsk.

Administratively the Yam Islands belong to the Magadan Oblast of the Russian Federation.

Zavyalov Island

Zavyalov Island (Russian: Остров Завьялова, or Ostrov Zav’yalova), formerly Ola Island (Остров Ольский), is a relatively large island in the Sea of Okhotsk, northwestern Pacific. It is located on the eastern side of Taui Bay, 20 km (12 mi) west of Cape Taran, Koni Peninsula, about 50 km (31 mi) south of the city of Magadan.

Zavyalov is a mountainous island; it is 23 km (14.3 mi) long and 7.5 km (4.6 mi) wide. The Siberian dwarf pine (Pinus pumila) and the dwarf birch Betula middendorffii grow on the island. Its shores are a breeding ground for the Steller sea lion.Administratively Zavyalov Island belongs to the Magadan Oblast of the Russian Federation.

Extant Carnivora species

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