STELLER SEA LION BIOLOGY
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fast facts | distribution | lifespan | diet | population decline | ​anatomy

steller-sea-lion-biology

Common Name
Steller sea lion, Steller’s sea lion, northern sea lion
Scientic Name
Eumetopias jubatus
Body Size
Male Steller sea lions average, a nose-to-tail length of 3 m and weigh about 700 kg.
Female Steller sea lions average 2.3 m in length and weigh about 300 kg.
Steller sea lions weigh about 20 kg when born (male pups are usually larger than female pups).
Physical Characteristics
Coloring: When dry, Steller sea lions are a tan to golden-brown color and darken to a chocolate brown on their flippers and underside. They appear dark brown or black when wet.
Coat: Male Steller sea lions have a thick mane. To protect themselves from the cold temperatures and from jagged rocks, Steller sea lions have thick coarse fur when dry, and smooth, slick fur that lies flat against the skin when wet. Stellers molt for about 4 weeks in the late summer, or early fall.
Insulation: Blubber is the main form of insulation of Steller sea lions.
Whiskers: Steller sea lions, like all pinnipeds, have well-developed facial whiskers which they use to sense prey and feel their way underwater.
Sounds
Steller sea lions make a low roaring sound.
Habitat
Steller sea lions range throughout the Pacific Rim (from southern California to Northern Honshu in Japan, and to the Bering Strait). About 70 percent of the Steller sea lion population resides in Alaska. Steller sea lions are highly gregarious and they use traditional haulout sites (an area used for resting) and rookeries (an area used for breeding and rearing young) on remote and exposed islands. These sites can be rock shelves, ledges, boulders, and gravel or sand beaches.
Climate
Steller sea lions prefer temperate climates.
Diet
Adult Steller sea lions eat a wide variety of fishes, including Pacific herring, sandlance, Atka mackerel, pollock, salmon, cod, and rockfishes. They also eat octopus and some squids. On average, an adult Steller sea lion requires about six per cent of its body weight each day. Young sea lions require twice this amount. See diet for more.
Predators
The main predators of Steller sea lions are killer whales, sharks and humans.
Reproduction
They mate and give birth on land. Births occur mid-May to mid-July and peak in June. In May, dominant males (nine years and older) establish their breeding territories on rookeries, and maintain them for approximately 40 days without eating. During this time, the males establish a harem and mate with many females on their territories, demonstrating their polygamous nature.Mating occurs soon after the birth of the previous year’s pups. The pups drink their mother’s milk, and they enter the water at four to six weeks. Some pups will nurse from one to three years, but most are believed to wean before their first birthday. Females give birth to one pup and may not give birth every year.

Pups are able to crawl and swim soon after birth. Females accept only their pups, recognizing their pup’s vocal and olfactory cues. Pups will approach other females, but are often bitten or thrown by females who have their own pups.

Males defend territories for an average of two years. There is a high incidence of aborted Steller sea lion fetuses in the wild. Pups are sometimes killed or injured from: a storm washing them away from a rookery, by adults tossing, biting, or crushing them, or by abandonment and disease.

Are Steller sea lions always in the water?
Steller sea lions are mammals, so they need to come to the surface to breathe air. They spend a portion of their time on the land and venture out in the water to hunt for food. Steller sea lions appear to prefer the coastal shelf region within 45 km of the shore, although they can be found over 100 km from the shore in waters exceeding 2,000 m deep. They do not migrate like some seals, but they do move seasonally to different feeding and resting areas.
Threatened Species
More than 80% of the Steller sea lion population disappeared from Russian and most Alaskan waters (Gulf of Alaska and Bering Sea) from 1980 to 2000, leaving fewer than 55,000 individuals. The United States listed Steller sea lions as “threatened” under the Endangered Species Act in 1990, and reclassified this western portion of the population as “endangered” in 1997. The population has stabilized in the Gulf of Alaska, but continues to decline in the western and central Aleutian Islands.

In the remainder of their Pacific Rim range, Steller sea lion numbers have nearly tripled – and now total over 150,000 animals between California and southeast Alaska.They are considered to be a species of Special Concern in Canada (due to having only 3 breeding sites) and were reclassified as not as risk in the United States in 2013.

Over 80% of the world’s population once lived in Alaska.

Why are Steller sea lions disappearing?
Scientists are currently researching why Steller sea lion populations are declining. Possible reasons for this include an increase in parasites, disease, predation by killer whales, quality and distribution of food, environmental factors and nutritional stress caused by natural changes in the abundance of key prey species, or by competition with other species orhumans for food.
The North Pacific Universities Marine Mammal Research Consortium
In 1993 the North Pacific Universities Marine Mammal Research Consortium, began to study the declining population of Steller sea lions. The Consortium is a group of graduate students and faculty members from the universities of Alaska, British Columbia, Washington and Oregon State. These researchers have undertaken a combination of field, captive and lab studies for research. The studies emphasize the effects of changes in types of prey on sea lion condition, health and energy balance. You can learn more about the Consortium on this web site.
Steller sea lions or harbour seals?
Steller sea lions are larger and have longer flippers. They are very vocal, territorial and can be aggressive with one another.

Sea lions are also able to support themselves on their front two flippers and can pull their hind flippers under their bodies to walk.

Sea lions swim with their front flippers, while seals swim with their hind flippers.

Seals have a smaller and sleeker torpedo shaped body. They rarely vocalize, are quite shy and are less gregarious than sea lions.

Seals do not use their flippers to support their bodies and move by sliding or shuffling.

Curious Facts
Males have a higher mortality rate than females.

By ten years of age, there is a 3:1 ratio of females to males.

It is difficult to study Steller sea lions in the wild, because Steller sea lions are extremely skittish, especially in the winter.

Stones are commonly found in Steller sea lions’ stomachs from pebbles to stones up to 12 cm in diameter!

Scientists are not certain if these rocks are swallowed by accident or if they serve a useful function.

It is speculated that they might help grind up fish, or act as a ballast when diving, or might help ward off hunger pangs when the animals are fasting on shore.

The deepest dive recorded for a Steller sea lion was 424 m.

 

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