Steller sea lion biology fast facts

Fast Facts

Common Name   Steller sea lion, Steller’s sea lion, northern sea lion
Scientific Name   Eumetopias jubatus
Body Size   Steller sea lions weigh about 21 kg when born (male pups are usually larger than female pups, with males weighing 22 kg and females 20 kg). They are almost 1 m long.

When fully grown, females average 2.3 m in length and weigh about 300 kg. However, males average, a nose-to-tail length of 3 m and weigh about 700 kg on average at the start of the breeding season (with some weighing over 1000 kg). 
Life Expectancy   Females live longer than males. The average age at death (life expectancy) is 4 years old for males and 10 years old for females. However, the longest some can live in the wild (i.e., longevity) is 16 years old for males and 23 years old for females.
Physical Characteristics   Colouring: When dry, Steller sea lions are a tan to golden-brown colour and darken to a chocolate brown on their flippers and underside. They appear dim- or dark-gray when wet.

Coat: Steller sea lions are covered in hair, that mainly protects them from jagged rocks.  Stellers molt (replace their coat) for about 45 days in the late summer, or early fall. For insulation from the cold water, sea lions rely on blubber — a thick layer of fat below the skin.

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.

  Steller sea lions belong to the group of mammals known as pinnipeds (“feather footed”), which refers to their wing-like flippers. Their pelvic bone structure allows sea lions to walk on their four web like flippers. In the water, the Steller sea lion pulls itself through the water using its front flippers. They can swim at top speeds of 27 km/hour (17 mph).  Other marine animals such as seals, swim with their hind flippers using a body action that is more fishlike.
Habitat   Steller sea lions range throughout the Pacific Rim (from southern California to northern Honshu in Japan, and to the Bering Strait). Genetically, there are three distinct populations called the Russian population, Western Population and Eastern Population. Steller sea lions are highly gregarious and use >600 traditional haulout sites (an area used for resting) and ~100 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, capelin, sand lance, Atka mackerel, walleye pollock, salmon, Pacific cod, rockfishes, salmon, flatfishes, sculpins, squid, octopus and occasionally seal pups. 

Most fish are swallowed whole. Large prey are torn apart and consumed at the surface. Sea lions sometimes feed in groups which may help to control the movement of large schools of fish and make them easier to catch. 

Diet appears to vary between regions and has also changed through time. The causes and consequences of these changes in diets are still under debate. 
On average, an adult Steller sea lion requires about 6% of its body weight each day. Young sea lions require twice this amount.

Predators   The main predators of Steller sea lions are killer whales, sharks and humans.
Reproduction   Steller sea lions mate and give birth on land. On average, females give birth for the first time when they are 5 years old. A few are as young as 3 years old. Births occur mid-May to mid-July and peak in June. 

In May, dominant males (9 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 females on their territories. On average, males successfully defend territories for only 2 breeding seasons. Mating occurs about 1 week following the birth of the pups. 

Pups are able to crawl and swim soon after birth, and enter the water at 4 to 6 weeks. 

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. 

Pups are sometimes killed or injured from: a storm washing them away from a rookery, by adult females tossing, biting, or crushing them, or by abandonment and disease.

The pups drink their mother’s milk. Some pups will nurse from 1 to 3 years, but most are expected to wean just before their first birthday. 

Females give birth to one pup and may not give birth every year. There is a high incidence of aborted Steller sea lion fetuses in the wild.

Are Steller sea lions always in the water?   Steller sea lions are mammals, so must come to the surface to breathe air. They spend a portion of their time on the land and venture out to sea to hunt for food. Steller sea lions prefer the coastal shelf region within 30 km of 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   Over 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. Recent increases have occurred in sea lion numbers in the Gulf of Alaska and Eastern Aleutians.
Why are Steller sea lions disappearing?   Scientists continue researching why Steller sea lions declined in the Gulf of Alaska, Aleutian Islands, and Russia. 

There are many hypotheses, which include an increase in parasites, disease, pollution, predation (by killer whales and sharks), and competition with other species or humans for food. Other hypotheses include reduced quality and distribution of food, poor environmental conditions, and increased nutritional stress caused by natural changes in the abundance of key prey species.  

Most of the scientific evidence points to the decline of the western population being caused by a natural shift in the prey base from fatty fish to lean fish that started in the late 1970s, which reduced sea lion birth rates and increased the death rates of young animals (the junk-food hypothesis).
Our research   We have been studying Steller sea lions since 1993 using a combination of field, captive and lab studies. Our research emphasizes the effects of changes in types of prey on sea lion condition, health and energy balance. Some of our findings can be found in the publication section.
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 physically 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.

In contrast, 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 on land, and move by sliding or shuffling.
Sea lions have small external ear flaps (pinnae) while seals do not.
Curious Facts   Males have higher mortality rates than females.
There are two females for every male aged 1 year and older. Beyond the age of 10, there are 5 times more females than males.

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

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

Scientists are not certain if sea lions swallow rocks by accident or if they serve a useful function. It is speculated that rocks 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.