Eared seals, fur seals, and sea lions

(Otariidae)

Class Mammalia

Order Carnivora

Suborder Pinnipedia

Family Otariidae

Thumbnail description
Medium- to large-sized pinnipeds that have large front flippers for underwater propulsion, a dog-like head, and the ability to walk or run on all fours on land

Size
Males range from 154 lb (70 kg) (Galápagos fur seal) to 2,469 lb (1,120 kg) (Steller sea lion); females range from 77 lb (35 kg) (Galápagos fur seal) to 772 lb (350 kg) (Steller sea lion); neonates range from 11 to 51 lb (5–23 kg)

Number of genera, species
7 genera; 15 species

Habitat
Feed in coastal or deep ocean areas, and they breed on sandy and rocky substrate, mostly on islands

Conservation status
Endangered: 1 species; Vulnerable: 5 species

Distribution
Bering Sea, north and south Pacific Oceans, south Atlantic Ocean, southern Indian Ocean, Southern Ocean; they occupy subpolar, temperate, and equatorial waters

Evolution and systematics

The most recent view is that all pinnipeds (walruses, true seals, and eared seals) had a single evolutionary origin. However, this should be considered a provisional view because the evolutionary sequences for these three groups are still incompletely known. Pinnipeds are most closely related to the arctoid carnivores, especially bear-like and racoon-like mammals. The current debate is whether walruses are more closely related to the true seals or the eared seals. The eared seals arose in the late early Miocene (20–15 million years ago) in the North Pacific. From there they moved south and diversified in the Southern Hemisphere where most species now live. Fur seals are considered to be older than sea lions. Callorhinus (northern fur seal) is the genus having the oldest lineage. Otariids are not perfectly separable into sea lions and fur seals; the Afro-Australian fur seal is intermediate between the two in behavior and anatomy.

Physical characteristics

All eared seals are sexually dimorphic. Males are two to four times larger, have proportionately larger heads, necks, and chests (related to fighting), and may have a wider range of colors than females. Otariids as a group are somewhat smaller than true seals as a group. The head is dog-like, and both sexes have sharp, dog-like canine teeth. The eyes are large, irises are brown, and the pupils usually close to a pinhole in bright light. The postcanine teeth, a series of intermeshing

points, are adapted for seizing prey, not for shearing or chewing. All species have small, cone-like external ears (hence the scientific name), unlike the true seals and walrus which have only an external auditory meatus (passageway). The vibrissae are well developed, white in adults, and 3–18 in (8–45 cm) long. The flippers are black and either hairless or have sparse hair. The pectoral muscles are well developed in both sexes and provide fore-flipper propulsion. Sea lions (Otariinae five genera, six species) have a pelage composed only of coarse guard hairs. The females are usually brown to light tan, whereas the males may vary from almost white to black. Fur seals (Arctocephalinae, two genera, nine species, two subspecies) have a pelage composed of guard hairs emerging from a dense, fine, brown, usually unseen underfur. Fur seal females are usually grizzled gray (black when wet) with light bellies, and males vary from white to reddish to black, depending on the species. Pups are usually black. Females make loud, prolonged calls related to finding their young. Males make a variety of calls, including repeated pulses (like barks), and prolonged calls.

Distribution

Four genera of otariids still inhabit the ancestral home of this family, the north Pacific Ocean (northern fur seal, Callorhinus ursinus; Steller sea lion, Eumetopias jubatus; California sea lion, Zalophus californianus; Guadalupe fur seal, Arctocephalus townsendi). All four co-occur only at San Miguel Island, California. Two species (Galápagos fur seal, A. galapagoensis, and sea lion, Z. wollebaeki) live at the equator, and two (South American sea lion, Otaria byronia, and fur seal, A. australis) are found along the Pacific and Atlantic coasts of South America and associated islands. One species (Juan Fernández fur seal, A. philipii) is confined to the Juan Fernández Islands off Chile. One species (Cape fur seal, A. pusillus pusillus) occurs around the tip of southern Africa, and a subspecies (Australian fur seal, A. p. doriferus) occurs only in Australia. New Zealand and Australia have one species of sea lion each (Hooker's [Phocarctos hookeri] and Australian sea lion, respectively), and the New Zealand fur seal (A. forsteri) is found in both places. The subantarctic fur seal (A. tropicalis) breeds on a series of islands from the latitude of New Zealand to the Antarctic Convergence. Finally, the Antarctic fur seal (A. gazella) breeds south of the convergence in the Atlantic and Indian Ocean sectors of the Southern Ocean, and extends as far south as the Antarctic Peninsula. The extent to which the distributions of modern otariids reflect the depredations of

nineteenth-century sealing, which nearly exterminated some species, is not known.

The at-sea distributions of otariids are poorly known because the main source of data has been satellite transmitters attached to foraging mothers. The two Galápagos species are believed to forage locally. But species like the subantarctic, Juan Fernández, and Guadalupe fur seals are known to forage over moderately large 580 mi² (1,500 km²) areas. The northern fur seal makes an annual migratory loop from breeding colonies as far north as the Bering Sea, south over the open ocean to about 35°N latitude, then north to the breeding islands again along the continental shelf break. The Antarctic fur seal may also migrate, but its pathway is less well known because it was never hunted at sea as the northern fur seal was.

Habitat

All otariids bear young and suckle on land. All mate on land, but at least four species also mate to a small degree in the water. They prefer islands, possibly because these sites afford more freedom from land predators, winds and spray that provide better cooling, and a shorter transit time to offshore feeding areas (or a combination of these benefits) than mainland sites do. Nevertheless, large mainland breeding sites now exist in Africa, Argentina, and Peru, and historically existed along the Pacific Coast of North America. Animals prefer breeding on sand or rock, and tend to avoid mud. Most species breed on beaches or headlands, but when the northern fur seal is numerous its colonies extend several hundred yards (meters) up hillsides. Hooker's sea lion breeds under trees on at least two islands, and often suckles its young under dense brush. The Antarctic and northern fur seals can tolerate snow, but do not habitually breed on ice. Where cold water is available, several species live in very hot climates. Otariids can climb nearly vertical surfaces, an ability that gives them access to land areas that true seals cannot use.

Otariids tend to use very few of the many land sites available to them. All species have a long (more than four month) period of neonate dependency, which forces mothers to alternate between feeding themselves and suckling. Land sites must be located where the feeding/nursing pattern is energetically feasible, and this may reduce the number of sites they can use. True seals wean young at a few days to weeks of age, and suspend feeding while nursing. Thus, they are not constrained to breed on sites that permit commuting to feeding areas, and, as a group, tend to breed in smaller groups at more sites than eared seals.

Fur seals tend to feed in the open ocean; sea lions tend to forage on the continental shelf.

Behavior

In most species, males arrive at breeding sites first and establish territories in habitat that females will later use (usually land but also water areas in hot climates). They maintain territories by fighting and by vocal and visual threat displays. The frequency and intensity of aggression depends largely on the turnover rate of adult males. It is most intense when males first come together as neighbors, and when they are not separated by rocks or ledges. In almost all species, males defend space, not females. In established colonies, territory holders are the largest, most mature males. But in colonization situations, subadult males may defend territories and do all the mating. No evidence has been found for hierarchies, but a lek system has been suggested for the California sea lion. All male otariids fast while defending territories. Northern fur seal males have been recorded fasting for 80 successive days with no food at all.

Reproductive females arrive on shore a day or so before giving birth and settle on a parturition (birthing) site, sometimes the same one used in previous years. Females of all species are gregarious but do not form social bonds or hierarchies that denote permanent status. Sea lion females tend to lie in body contact with each other, but fur seal females usually do not. Females regulate space by making low-level threats. As parturition nears, females of some species may become more aggressive, separate from the group, and appear to hold a territory (Steller sea lion) until estrus approaches. Fostering has been seen in four of the otariid species; the others suckle only their own young.

The attempt by males to herd or control females varies by species. Northern fur seal and South American sea lion males may bite and injure females while herding them, but Steller and Hooker's sea lion males rarely touch or interfere with females. The term "harem" is an inappropriate term to describe social organization in most otariids because it implies an exclusivity in mating access that usually does not exist. Males interact with females frequently as estrus approaches, but may simply approach and mount when the female is fully receptive.

Females mate usually once per estrus, and usually depart on their first foraging trip soon after. When they return the lack of a formal social structure allows them to rejoin the group without aggression. Females interact with their young intensely after birth and after foraging absences, but play with them very little, and protect them only moderately from other females.

The young are precocial. They can swim on the day of birth if forced, and they spontaneously show components of adult behavior, such as copulation and fighting, in the first weeks of life. They gather in groups during the mothers' absence.

Juvenile males gather on the fringes of breeding groups, but juvenile females may join those groups, before or after the peak of mating.

Feeding ecology and diet

As stated previously, fur seals tend to forage on the high seas, and sea lions tend to forage near the coast. Fur seals are

fairly small (females average less than 110 lb [50 kg]), and can thrive on large numbers of small fish (like myctophids) and squid that rise to the surface at night in association with the deep scattering layer. The Antarctic fur seal exploits euphausids (krill) that undergo similar vertical migrations. Fur seal females can dive to 656 ft (200 m) or so, which enables the largest of them to feed on the bottom where the continental shelf is broad and productive.

Sea lion females may dive to 1,312 ft (400 m) or so, and generally take small numbers of larger fish and squid that are

part of the continental shelf fauna. Unlike fur seals, which suspend feeding in the middle of the day when their prey are at maximum depth, sea lions may forage night and day without stopping. Their greater energy needs may preclude them from exploiting the smaller organisms of the deep scattering layer. Both groups are capable of exploiting silvery schooling fish, such as herring, anchovy, or sardines, wherever they are encountered.

The length of the mothers' feeding absence depends on the foraging environment they use, and therefore tends to be longer for fur seals than for sea lions. The shortest trips are made by the equatorial species that feed locally (a few hours to one day). The longest trips are made by the temperate fur seals (Guadalupe, Juan Fernández, subantarctic, and some populations of the New Zealand fur seal) that feed on organisms of the deep scattering layer. Pup fasting ability varies accordingly.

Most sea lion species (males only) have been observed preying on other species of seals, but fur seals have not. Both groups occasionally eat birds. Otariids are visual feeders; echolocation has not been demonstrated for any species, although researchers have looked for this ability in the laboratory.

Reproductive biology

Otariids are strict annual breeders except for the Australian sea lion which, for reasons yet unknown, follows an unusual 17.5 month cycle. Females of all species bear a single, large pup per season. Twins are rare (1 in 10,000 births) in some species. The uterus is bicornuate (has two sections), which allows females to undergo a postpartum estrus. All otariids, including the Australian sea lion, undergo an embryonic diapause (delayed implantation) for about four months before the embryo implants and begins active growth. Diapause seems to function as a timing mechanism, insuring that births occur near particular dates. The timing can be quite precise; in northern and Antarctic fur seals, individual females give birth within three to four days of the same date (specific to each female) in successive years.

All otariids are polygynous; adult sex ratios of 60 females per adult male have been observed in populations subjected to sealing, but undisturbed sex ratios are typically between 2:1 and 10:1. Polygyny is an apparent result of several factors, including breeding at a few large colonies instead of many small ones, gathering at a predictable time and place, higher agespecific mortality in males than in females, length of the

breeding season, male competition rate, and a postpartum estrus. Males may mate 100 or more times during a breeding season, depending on their location relative to females.

Females have a single estrus that occurs less than 10 days postpartum (except in the California sea lion where it is 30 days). Most females mate only once per estrus, rarely twice. If they fail to mate, estrus may last less than two days (36 hours in the northern fur seal). If they mate, estrus may be terminated by coitus (the Whitten effect). Females of most species mate indiscriminately with whichever male is nearest when they enter estrus. Females usually do not mate with juvenile or peripheral males because adult males exclude them from the breeding sites. However, in colonization situations, when males intercept females on their way to feeding (South American and Hooker's sea lions), or in captivity, females of some species readily mate with juvenile or peripheral males. Pregnancy rates may exceed 90% in some age classes of females.

The duration of the breeding season varies with latitude. The interval in which 90% of the females enter estrus varies from 21 days in the Antarctic fur seal to 70 days in the Galápagos fur seal. Many aspects of the social system change when the breeding season is long lasting.

Conservation status

Most otariids were exploited by nineteenth-century sealers to some extent. Fur seals were exploited most heavily because their pelts, with guard hairs removed, were prized for clothing. Sea lions were taken mostly for oil, hides, vibrissae, and organs. After a very long lag time (50–60 years) fur seals are showing better recovery from sealing than sea lions, and at present seem to be thriving somewhat better. The most spectacular recovery was made by the Antarctic fur seal, which was once believed to be extinct and now numbers 3–4 million animals. All fur seals are presently increasing except the northern fur seal. This species recovered from nineteenth-century sealing and reached a peak in 1956, but has been declining ever since. Because the reason for this decline is unknown, there is as much concern for this species as there is for those that have smaller total numbers (Guadalupe, Juan Fernández, South American, subantarctic fur seals) but a good growth rate. The Galápagos fur seal recovered from sealing, but its total numbers appear to be limited now by periodic El Niño events that depress adult survival. The Galápagos, Juan Fernández, Guadalupe, and northern fur seal are all listed as Vulnerable by the IUCN.

Sea lions are harder to summarize. California and South American sea lions are increasing. The Galápagos sea lion

seems to be limited by El Niño events like Galápagos fur seals. Hooker's sea lions are of concern because, while never present in large numbers, they have been stable for 20 years and are facing competition with a squid fishery. The Steller sea lion has declined by more than 90% in the last 20 years and may be impacted by a commercial fishery. The Stellar sea lion is listed as Endangered, and Hooker's sea lion is Vulnerable.

Significance to humans

Fur seals were formerly a source of pelts from which clothing was made. From 1760 to about 1900, they were the subjects of intense international trade, treaties, and even small wars. A more controlled form of trade continued until 1985 when the last commercial sealing ended. Since the 1970s otariids have been increasingly seen as competitors of commercial fishing operations, or a problem in fisheries bycatch. All pinnipeds are used as scapegoats to explain declining fisheries catches.

Species accounts

List of Species

Northern fur seal

Callorhinus ursinus

subfamily

Arctocephalinae

taxonomy

Callorhinus ursinus (Linnaeus, 1758), "Bering Island."

other common names

English: Sea bear; French: Otarie des Pribilofs; German: Nördliche Pelzrobbe; Spanish: Lobo fino del norte.

physical characteristics

Males to 606 lb (275 kg), gray to black or reddish. Females to 110 lb (50 kg), gray. Rear flippers long and slender; hair on front flippers stops abruptly at the wrist joint. In all other otariids hair extends beyond the wrist joint.

distribution

The species breeds from southern California to the Kuril Islands with the main populations at the Pribilof and Commander Island groups. Females and juveniles forage south to 35°N latitude, then migrate back to breeding sites in spring.

habitat

This species now breeds exclusively on islands (formerly on the mainland). One of the breeding sites is known to have been used for over 250 years. It is one of the most pelagic otariids, spending all but 35–45 days per year at sea.

behavior

It follows the basic otariid behavior, described above. It forms only a few large breeding colonies where males fast while defending terrestrial territories. Females arrive on predictable dates, form amorphous social groups, give birth, mate, then alternate foraging with nursing until weaning at four months. Females and males are highly site specific.

feeding ecology and diet

The species takes over 75 species of fish and cephalopods, many of them associated with the deep scattering layer. The diet was determined by extensive collections at sea.

reproductive biology

Polygymous. The notion of seal harems may have developed with this species. The species does not deviate from the basic otariid pattern, except that females wean young at four months of age. More is known of its reproductive biology than other species because an international treaty (1911 to 1985) mandated certain kinds of research.

conservation status

The species is listed as Vulnerable, and numbered only a few hundred thousand in 1911, increased to 2.5 million in the mid 1950s, then declined to approximately 1 million in 2002. The

reasons for the decline are unknown, but it is proceeding in parallel with decreases in the Steller sea lion, harbor seal, and sea otter in Alaska.

significance to humans

The species was of great significance to society from the 1860s to 1985 because of pelts. It was the first marine mammal to which a management regime was applied, and it was the subject of an international treaty in 1911. Presently Alaska natives use the species for subsistence.

Antarctic fur seal

Arctocephalus gazella

subfamily

Arctocephalinae

taxonomy

Arctocephalus gazella (Peters, 1875), "Anse Betsy" 49°09'S, 70°11'E.

other common names

English: Kerguelen Island fur seal; French: Otarie antarctique; German: Kerguelen-Seebär, Antarktischer Seebär; Spanish: Lobo fino antarctico.

physical characteristics

Males to 114 lb (200 kg); 1–2% of them are white but not albino. Females are gray, to 110 lb (50 kg).

distribution

Occurs mostly on subantarctic islands. Large populations are found south of or close to the Antarctic polar front, with 95% of the population breeding on South Georgia.

habitat

The species breeds on islands in the south Atlantic and south Indian Ocean sectors of the Southern Ocean. It abandons land areas in winter, but its pelagic distribution is unknown. It is fully as pelagic as the northern fur seal. Most breeding sites are south of the Antarctic Convergence. Like the northern fur seal, it tolerates snow but does not breed on ice.

behavior

This species follows the description of otariid behavior given above. Males fast and are territorial, females form dense aggregations, and lack a specific form of social organization.

feeding ecology and diet

This is the only otariid that frequently feeds on euphausids (krill). It also takes fish, crustaceans, and some birds. It feeds at night at shallow depths over deep water in association with the deep scattering layer.

reproductive biology

Polygynous. It deviates from the usual otariid reproductive biology only in that females wean their young at the age of four months. Their breeding seasons are short, as expected for the length of summer at their breeding sites. Antarctic fur seals sometimes hybridize with subantarctic fur seals at Marion Island.

conservation status

Not threatened. The species appeared to be extinct in the late 1800s. Its recovery may have been aided by commercial whaling in the 1940s and 1950s, which removed the fur seal's major competitor for krill. The population has been increasing at 9% or more annually, and now exceeds 3 million animals.

significance to humans

It was formerly the subject of intense international competition for pelts. At present it is of no particular significance to humans.

Hooker's sea lion

Phocarctos hookeri

subfamily

Otariinae

taxonomy

Phocarctos hookeri (Gray, 1844), "Falkland Islands and Cape Horn" (in error, actually "Auckland Islands").

other common names

English: Auckland sea lion, New Zealand sea lion; French: Lion de mer de Nouvelle-Zélande; German: Neuseeland-Seelöwe; Spanish: Léon marine de Nuevo Zelandia.

physical characteristics

Males to 992 lb (450 kg), nearly black; females to 364 lb (165 kg), light tan in color. Pups of various colors with a light stripe down the nose.

distribution

Ocean near Auckland Islands, Campbell Island, and other islands near New Zealand.

habitat

The species breeds on protected beaches on three islands of the Auckland Island group, Campbell Island. It hauls out on many other islands in the New Zealand area. Animals may breed on sand or under shoreline trees.

behavior

The species forms relatively small colonies. Males are territorial, and females form a dense aggregation. At Enderby Island the female aggregation moves along the beach parallel to the water line during breeding. Juvenile males intercept females departing for foraging, and may mate. After the breeding season females move inland to suckle their young in the forest.

feeding ecology and diet

The species is reported to take 33 species of prey (fish 59% of diet, cephalopods 22%, crustaceans 15%). Females are largely bottom feeders, dive night and day continuously while at sea, and reach maximum depths of 1,312 ft (400 m). Males occasional take penguins, and cannibalism has been reported. Females often regurgitate rocks and octopus beaks.

reproductive biology

Polygynous. The females wean their young by one year of age. No major deviations from typical reproductive biology are known.

conservation status

Listed as Vulnerable. Hooker's sea lions were formerly more abundant and widespread before being reduced by commercial and subsistence (Maori) sealing. The present population is estimated at 13,000. Its numbers have been stable for 20 years.

significance to humans

Bycatch in a squid fishery on the Auckland shelf may threaten this species.

Australian sea lion

Neophoca cinerea

subfamily

Otariinae

taxonomy

Neophoca cinerea (Péron, 1816), Kangaroo Island, Australia.

other common names

English: White-capped sea lion; French: Lion de mer d'Australie; German: Australischer Seelöwe; Spanish: Lobo marino de Australia.

physical characteristics

Males are dark brown to nearly black with a white patch on the head and nape of the neck. They weigh more than 441 lb (200 kg). Females weigh up to 231 lb (105 kg), and have a white belly and tan back.

distribution

Ocean off the southern coast of Australia.

habitat

This species breeds in protected locations at many sites along the southern coast of Australia. Females seek holes in rock or under brush to bear and suckle young. More than 50 breeding colonies are known, only five of which produce more than 100 young per year.

behavior

Australian sea lions are territorial like other otariids, and females form groups. They will not flee when approached by humans. Many aspects of their behavior are altered by the long breeding season.

feeding ecology and diet

The species takes a combination of cephalopods, crustaceans, and fish. It often feeds on the bottom, and has been known to take lobsters from inside fishing pots.

reproductive biology

Polygynous. This species has the most unusual reproductive biology of any otariid. Females have a 17.5-month breeding cycle; colonies breed out of synchrony with each other. The breeding season lasts five months. Individuals have strong site fidelity.

conservation status

Not threatened. The species was once hunted for skins and oil but was probably never as numerous as the local fur seals. Their numbers are now estimated at 9,300–11,700. Their potential for further increases is limited by the low productivity of their limited feeding habitat.

significance to humans

Tourist attraction on Kangaroo Island. Here and elsewhere the species shows little fear of humans.

South American sea lion

Otaria byronia

subfamily

Otariinae

taxonomy

Otaria byronia (Blainville, 1820), "Island of Tinian (in error, probably strait of Magellan).

other common names

French: Lion de mer d'Amérique du Sud; German: Mähnenrobbe, Südamerikanischer Seelöwe; Spanish: Lobo común.

physical characteristics

Males to 772 lb (350 kg), brownish in color with a rough mane and unusually large neck and head. Females to 331 lb (150 kg), tawny.

distribution

Ocean near the Falkland Islands and eastern coast of South America.

habitat

Breeds on sand, cobble, or rock. Found on the Falkland Islands, from southern Brazil to Cape Horn (more than 53 breeding sites in central to southern Patagonia), and north to Peru.

behavior

Animals do not make prolonged foraging absences, nor do they migrate. Some colonies are occupied all year. Mating is seasonal. Males display a variety of mating strategies in addition to territoriality. Males vigorously herd females, sometimes injuring them.

feeding ecology and diet

The species takes fish, crustaceans, and cephalopods. Males occasionally take young fur seals and penguins. Females make short (three day) foraging trips, typical for sea lions.

reproductive biology

Polygynous. The operational sex ratio is 1.2 females per male. As with other otariids, females bear a single pup per year, and have a postpartum estrus.

conservation status

Not threatened. The species was commercially exploited for oil, and is still killed by fishermen. The population is presently estimated at more than 110,000, which may be 20% of its original numbers. Numbers may be increasing. Populations in the Pacific decline in response to El Niño events.

significance to humans

The species is being taken as bait for king crab pots, and is considered to be a nuisance by other fishermen.

California sea lion

Zalophus californianus

subfamily

Otariinae

taxonomy

Zalophus californianus (Lesson, 1828), San Francisco Bay, California, United States.

other common names

English: Black sea lion; French: Lion de mer de Californie; German: Kalifornischer Seelöwe; Spanish: Lobo marino de California.

physical characteristics

Males black/brown with a prominent saggital crest topped by white hair. The call is a loud, sharp bark. Males to 772 lb (350 kg), females to 220 lb (100 kg), tawny.

distribution

Ocean from central Mexico to southern California, including Guadalupe Island and the Sea of Cortez. Males migrate north as far as Canada, but females do not.

habitat

Breeds on sand or rock from central Mexico to southern California (plus Guadalupe Island and the Sea of Cortez). No mainland breeding sites now exist.

behavior

The most successful males defend territories that afford females access to water. Female aggregations move across the beach depending on daily temperatures. This species may perform more aquatic copulations than other otariids.

feeding ecology and diet

These are opportunistic feeders, primarily depending on anchovy, whiting, rockfish, cephalopods, mackerel, myctophids, sardines, etc., depending on location, season, and El Niño events. Animals feed at all hours. Feed in groups, and may feed with Steller sea lions where the ranges overlap (San Miguel and Año Nuevo Island, California).

reproductive biology

Polygynous. Male biology is typical for otariids. Female California sea lions enter estrus 30 days postpartum, instead of less than 10 days like other otariids. Breed on islands with northern fur seals, but hybrids are not known.

conservation status

Not threatened. California sea lions were exploited in the nineteenth century, and reached a low of 1,500 in the 1920s. They then increased, displacing the Steller sea lion as the most numerous sea lion in California. Their numbers are now between 211,000 and 241,000 and are growing at 5% per year.

significance to humans

This species is known as the common "circus seal," and has served to introduce generations of humans to the family Otariidae. As a laboratory animal, the species has contributed significantly to what we know about vision, hearing, learning, and cognition in marine mammals. Some consider it a nuisance because it is noisy, increasing, and likely to foul the many human structures (buoys, piers, etc.) it uses as resting sites.

Galápagos sea lion

Zalophus wollebaeki

subfamily

Otariinae

taxonomy

Zalophus wollebaeki Sivertsen, 1953.

other common names

German: Galapagos Seelöwe.

physical characteristics

Males are gray/brown to black; no weights reported. Their call is a sharp, intense bark. Females are tawny, and weigh up to 176 lb (80 kg).

distribution

Galápagos Islands. It is restricted to feeding in upwelling plumes around the islands and cannot emigrate during El Niño events.

habitat

The Galápagos sea lion breeds on all the major islands of the Galápagos. It prefers gently sloping beaches of sand and rock, and therefore shares no breeding sites with the Galápagos fur seal.

behavior

Their behavior has not been well studied, but appears to resemble that of California sea lions in general. It defends shoreline territories. Most animals are on shore at night.

feeding ecology and diet

These animals forage usually in the daytime on sardines (70% of diet). They may switch to green eyes and myctophids during El Niño events.

reproductive biology

Polygynous. The species maintains an annual cycle of breeding, and has a long (6–8 month) breeding season. Females suckle young for two years on average (range 1–3 years), and may simultaneously suckle a pup born that year.

conservation status

The species was not commercially exploited. It numbered to 50,000 in 1963, but declined to 14,000 after the 1997–98 El Niño event. It may now be below historic numbers.

significance to humans

An ecotourism attraction as part of the native fauna of the Galápagos Islands.

Steller sea lion

Eumetopias jubatus

subfamily

Otariinae

taxonomy

Eumetopias jubatus (Schreber, 1776), Commander and Bering Islands, Russia.

other common names

English: Northern sea lion; French: Lion de mer de Steller; German: Stellers Seelöwe; Spanish: Lobo marine de Steller; Aleut: qawax; Russian: Sivuch.

physical characteristics

This is the largest of the otariids. Males are reddish or dark brown to nearly white, average 1,248 lb (566 kg), and reach a maximum of 2,469 lb (1,120 kg). Females are tan, average 580 lb (263 kg), and reach a maximum of 772 lb (350 kg). Pups are chocolate, wooly, and weigh approximately 44 lb (20 kg) at birth.

distribution

Ocean from central California to the Kuril Islands.

habitat

They breed on rock, sand, or cobble beaches from central California to the Kuril Islands with the population peak in the Aleutian chain. They breed on islands except at one site, a cave in Oregon. Where the ranges overlap, Steller sea lions have extensive contact with California sea lions and northern elephant seals. No hybrids are known.

behavior

Males are territorial, and females form aggregations, often very dense because of their tendency to rest in full body contact with others. Females move to the water's edge in hot weather.

feeding ecology and diet

The species takes a wide variety of fish and cephalopods, including walleye pollock, cod, mackerel, flatfish, small schooling fish, salmon, and occasionally birds or other seals. Feeds at all hours of the day, often in groups.

reproductive biology

Polygynous. They have a predictable annual breeding season. Most females wean young by one year of age, but a few return to breeding sites still suckling two to three year-old young.

conservation status

Listed as Endangered. The species has been declining in California since the 1920s. Their overall numbers have declined by 90% since the 1980s, especially in the central Aleutian Islands. In 1994 a census revealed 100,000 animals, but the number may now be as low as 75,000.

significance to humans

The population decline may be linked to commercial fishing for walleye pollock, the largest single-species fishery in the United States. The legal, financial, and research implications of this possible impact are having significant effects on many aspects of human society at present. The species is declining in parallel with northern fur seals, harbor seals, and sea otters in Alaska.

Resources

Books

Berta, A., and L. Sumich. Marine Mammals: Evolutionary Biology. San Diego: Academic Press, 1999.

Gentry, R. L. Behavior and Ecology of the Northern Fur Seal. Princeton: Princeton University Press, 1998.

Perrin, W. F., B. Würsig, and J. G. M. Thewissen. Encyclopedia of Marine Mammals. San Diego: Academic Press, 2002.

Riedman, M. The Pinnipeds: Seals, Sea Lions and Walruses. Berkeley: University of California Press, 1990.

Trillmich, F., and K. A. Ono, eds. Pinnipeds and El Niño. Berlin: Springer-Verlag, 1991.

Roger Gentry, PhD