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Eumetopias jubatusSteller sea lion

By Danielle Keranen

Geographic Range

Steller sea lions are distributed along the North Pacific Ocean and prefer cold to sub-arctic water, they are mainly found around the coasts out to the outer continental shelf. Primarily, they are found along the northern California coast, Alaska, and the coasts of Russia and Japan. Steller sea lions are considered endangered west of 144º W latitude and threatened east of 144º W latitude. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

Habitat

Steller sea lions are found in the cold waters of the Pacific Ocean on rookeries (breeding grounds) and near haul outs (non-breeding grounds). Within these areas, there is a 37 kilometer (20 nautical miles) radius where Steller sea lions typically are found. These areas are protected by the species recovery plan. Steller sea lions are able to dive as far as 400 meters (1,312 feet) and can stay under water for up to two minutes. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

  • Range depth
    400 (high) m
    1312.34 (high) ft

Physical Description

Steller sea lions are the largest eared seals and the fourth largest pinniped in the world. Steller sea lions are sexual dimorphic, meaning the males are noticeably larger than the females. Another distinguishing characteristic of male Steller sea lions is their thick mane of coarse hair. Males can weigh up to 1,120 kilograms (2,500 pounds); whereas, females weigh up to 350 kilograms (770 pounds). Pups range from 16 to 22.5 kilograms (35 to 50 pounds). Males can reach lengths up to 3 to 3.4 meters (10 to 11 feet), while females reach 2.3 to 2.9 meters (7.5 to 9.5 feet). The coloring of the adult Steller sea lions ranges from light blonde to reddish brown, with slightly darker coloration of the chest and stomach. When Steller sea lions are wet, the light coloration on their body is still visible, which make these sea lions unique to other pinnipeds. Similar to other pinnipeds, Steller sea lions molt their winter coat yearly. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

  • Sexual Dimorphism
  • male larger
  • Range mass
    350 to 1,120 kg
    770.93 to lb
  • Range length
    2.3 to 3.4 m
    7.55 to 11.15 ft

Reproduction

Steller sea lions have a polygynous mating system. Dominant males are the only males permitted to mate; however, younger males sneak onto rookeries and try to mate with females without dominant male noticing. Females become sexually mature between the ages of three to six years and give birth to a single pup between mid-May and July. Female Steller sea lions are ready to mate 2 weeks after giving birth; however, the fertilized egg won’t become implanted in the uterus for several months. Dominant males guard and mate with up to 30 females during one mating season. The number of females that are successfully bred has been decreasing over the years. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)

Steller sea lions breed, give birth and nurse young on remote islands called 'rookeries'. Females give birth to a single pup. Gestation lasts a year, including a three month period where the fertilized egg isn’t implanted in the female’s uterus. Pups are weaned in one year, but mothers can continue to suckle young for up to three years. At birth, pups weigh between 16 to 23 kilograms (35 to 50 pounds) and are about 1 meter (3.3 feet) long. Both male and female Steller sea lions reach sexual maturity between the ages of three to six years. Due to the competition between males, most are unlikely to breed successfully until the age of eight or ten. Rookeries are occupied during the summer months by dominant males, females, and the pups born during that year. Breeding occurs on the rookeries during the summer months. Yearlings and older juveniles do not stay on the rookeries as long because they are unable to breed. The rookeries break-up during August, at this time, females and young move to a different island, this is called a 'haul-out'. Steller sea lions are generally very social animals and continue to live with one another after the breeding season. During non-breeding periods, Steller sea lions go to beaches and lay out together. (Gelatt and Lowry, 2012; Horning and Mellish, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)

  • Breeding interval
    Steller sea lions breed once a year, after their pup is born.
  • Breeding season
    Steller sea lions breed during the summer months.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    12 months
  • Average gestation period
    274 days
    AnAge
  • Range weaning age
    12 to 36 months
  • Average weaning age
    12 months
  • Range age at sexual or reproductive maturity (female)
    3 to 6 years
  • Range age at sexual or reproductive maturity (male)
    3 to 10 years
  • Average age at sexual or reproductive maturity (male)
    8-10 years

Female Steller sea lions provide care for their young for as long as three years. They nurse their young for up to a year, but some will let their young nurse longer. Male Steller sea lions do not provide much parental care for their young; however, males will guard all the females that they impregnated. After female Steller sea lions give birth, they forage around the rookery and onshore, mostly at night, and may be gone for as long as a day. After finding a food source, they return and nurse their pup. (Gelatt and Lowry, 2012; Horning and Mellish, 2012; NOAA Fisheries, 2012)

Lifespan/Longevity

Male Steller sea lions can live up to 20 years; whereas, females can live up to 30 years. Their lifespan in captivity has not been reported. The main cause of death for Steller sea lions is old age. They are sometimes killed by fisherman because they interfere with fishing nets and fish hatcheries. (Gelatt and Lowry, 2012)

  • Typical lifespan
    Status: wild
    20 to 30 years

Behavior

Steller sea lions are generally social within their populations and can be found in large groups in rookeries or on beaches. Steller sea lions are usually found in groups ranging from one to twelve, but have been seen with as many as a hundred individuals on a beach. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

Home Range

Steller sea lions are typically found along California and further north on the west coast of North America. Likewise, they may also be found in Alaska, Japan, the Gulf of Alaska, and the Bering Strait. Young Steller sea lions usually travel farther than adults, because they are unable to mate they will go farther for food. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)

Communication and Perception

Steller sea lions communicate with other individuals though low frequency vocalizations that sound like a roar, as opposed to their relative, the California sea lion, whose vocalizations sound more like a bark. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

Food Habits

Steller sea lions forage for food along the shoreline and near pelagic waters and are considered opportunistic hunters. Their main food sources include walleye pollock, Atka mackerel, Pacific salmon, and Pacific cod. In the winter, walleye pollock and Pacific cod are their main food source. Atka mackerel is their most common food source all year long. Steller sea lions will also eat octopus, squid, bivalves, and gastropods. Steller sea lions have also been known to kill other animals, such as harbor seals and ringed seals, along with younger northern fur seals. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)

  • Animal Foods
  • fish
  • mollusks
  • cnidarians

Predation

Salmon sharks, killer whales, and Pacific sleeper sharks are some of their known predators. The recovery of Steller sea lions is related more strongly to predator abundance than resource abundance. Great white sharks have been known to kill and consume Steller sea lions if their territories happen to cross. Humans may also prey on Steller sea lions. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012; Sinclair and Zeppelin, 2002)

Ecosystem Roles

This species preys on a variety of fish, bivalves, gastropods, and cephalopods. (Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

Economic Importance for Humans: Positive

Historically, Steller sea lions were hunted for their meat, fur, and oil; this played a part in the decrease of their population. Incidental population destruction has also occurred due to fishing nets, ship strikes, pollutants and diseases. (Bickham, et al., 1996; Gelatt and Lowry, 2012; NOAA Fisheries, 2012)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

Steller sea lions are thought to deplete fish stocks and eat fish out of hatcheries, so they are often killed or hunted. (Gelatt and Lowry, 2012)

  • Negative Impacts
  • crop pest

Conservation Status

Throughout most of its range (west of the 144º W latitude), Steller sea lions are considered endangered, while in other parts (east of 144º W latitude), they are considered threatened. Populations of Steller sea lions are declining due largely to culling by fisherman. Historically, Steller sea lions have also been harvested for their fur, blubber, and meat. (Gelatt and Lowry, 2012)

Contributors

Danielle Keranen (author), Michigan Technological University, Amy Schrank (editor), Michigan Technological University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

external fertilization

fertilization takes place outside the female's body

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

food

A substance that provides both nutrients and energy to a living thing.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

piscivore

an animal that mainly eats fish

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"

tactile

uses touch to communicate

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Bickham, J., J. Patton, T. Loughlin. 1996. High Variability for Control-Region Sequences in a Marine Mammal: Implications for Conservation and Biogeography of Steller Sea Lions (Eumetopias jubatus). Journal of Mammalogy, Volume 77/ Issue 1: 95-108.

Gelatt, T., L. Lowry. 2012. "Eumetopias jubatus" (On-line). The IUCN Red List of Threatened Species. Accessed December 19, 2012 at http://www.iucnredlist.org/details/8239/0.

Horning, M., J. Mellish. 2012. Predation on an Upper Trophic Marine Predator, the Steller Sea Lion: Evaluating High Juvenile Mortality in a Density Dependent Conceptual Framework. PloS One, Volume 7/ Issue 1: 1-10.

Kenyon, K., D. Rice. 1961. Abundance and Distribution of the Steller Sea Lion. Journal of Mammalogy, Volume 42/ Issue2: 223-234.

NOAA Fisheries, 2012. "Steller Sea Lion (Eumetopias jubatus)" (On-line). NOAA Fisheries Office of Protected Resources. Accessed November 19, 2012 at http://www.nmfs.noaa.gov/pr/species/mammals/pinnipeds/stellersealion.htm.

Sinclair, E., T. Zeppelin. 2002. Seasonal and Spatial Differences in Diet in the Western Stock of Steller Sea Lions (Eumetopias jubatus). Journal of Mammalogy, Volume 83/ Issue 4: 973-990.

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