Scientific name: Eumetopias jubatus
Family: Steller sea lions are the largest of the otariids and the fourth largest of the pinnipeds, meaning “feather” or “fin” footed.
Lifespan: Males rarely live beyond their mid-teens, while females may live as long as 30-years.
How Many: Approximately 45,000 in the Western Population, and 63,000-78,000 in the Eastern Population (Allen, B.M and R.P Angliss, 2014)
Length and weight: The average adult male Steller sea lion is about 1,250 lbs. They can get up to 10-11 ft in lenght and weigh up to 2,500 lbs! Adult females are from 7.5-9.5 ft in length and can weigh up to 770 lbs. At birth, Steller sea lions weigh about 35-50 lbs and are about 3 feet in length.
Color: Adult Steller sea lions are light brown to blond with a dark brown darkening around the flippers and undersides. Steller sea lions are dark brown at birth.
Behavior: Steller sea lions are very vocal with grumbles, growls, and roars. Roaring males often bob their heads up and down when vocalizing. Adult males establish territories and aggressively defend them. Steller sea lions gather on haulouts and rookeries and regularly travel great distances (up to 250 miles) to find food. They can travel much further and juvenille sea lions have been known to travel over 1,000 miles. However, females with pups likely forage much closer to their rookery. Diving is generally to depths of
600 feet or less and diving duration is usually 2 minutes or less.
Body: Steller sea lions have large, bulging eyes, and flat, square noses. Steller sea lions also have long whiskers which are used to navigate underwater and find prey. The ears of a Steller sea lion are visible and are turned downwards so that water does not enter them when the sea lions go underwater. When adult males age, they develop a “mane” of long, coarse hair. Steller sea lions are particularly agile on land and swim using their foreflippers. Adult males grow 2-3 times as large as an adult female. Adult males have thickened necks and triangular shaped heads. Both male and female sea lions have large front and rear flippers.
Habitat: Steller sea lions inhabit the cool coastal waters of the North Pacific. When not in the water, Steller sea lions gather on rookeries and haulouts which are secluded rocky islands.
Food habits: Steller sea lions are opportunistic and eat a wide range of fish including herring, pollock, salmon, cod and rockfishes, sculpin, Atka mackeral, capelin, as well as squid, shrimp and other fish. To survive, an adult sea lion needs to eat at 5-6% of its body weight each day, but young animals need twice that amount. When males are defending their territories on the rookeries, they may go without eating for over a month! Interestingly enough, Steller sea lions do not need to drink water because the food they eat provides them with all the water they need. Sea lions do not chew their food, most is swallowed whole. Feeding often occurs in groups and they often feed at night between 9 PM and 6 AM.
Life History: Adults return to land to breed and give birth at rookeries.
Steller sea lions become sexually mature at 3 to 7 years of age and mate and give birth on land. Males usually arrive at a rookery in May and stake out their territories for up to 60 days. Females arrive later and usually give birth to a pup that was conceived the prior year. A pregnancy lasts about 11 ½ months and lactation continues for 1 to 3 years. Mating occurs shortly after the pups are born, during June and July.
Predators: Include humans, sharks, and killer whales.
Stocks/Populations of Steller Sea Lions: Under the MMPA, two stocks are recognized for Steller sea lions – an Eastern Stock and a Western Stock. Under the ESA, they are considered “Distinct Population Segments” or DPS. The separation between the two stocks occur at Cape Suckling, 144 degrees West longitude, between Prince William Sound and Yakutat in Southeast Alaska. The Western stock extends from Cape Sucking westward to include Prince William Sound, Cook Inlet, Kodiak Island, Bristol Bay, the Bering Sea, Aleutian Islands, Russia and Japan. The Eastern stock extends eastward from Cape Sucking to include Southeast Alaska, British Columbia, Washington, Oregon and California.
Population Status: Before it was recognized that there were two populations of Steller sea lions, the species was listed as threatened under the Endangered Species Act in 1990. When it was listed as Threatened, it was automatically classified as “Depleted” under the MMPA. In 1997 it was recognized that a Western and Eastern populations of sea lions existed. Due to continuing population declines, the Western population was uplisted to Endangered Status under the ESA. The Eastern population retained its Threatened designation despite continuing population increases. In 2012, the National Marine Fisheries Service began its regular Status Review of listed species, and proposed to delist the Eastern stock based it meeting the delisting targets identified in the Steller Sea Lion Recover Plan. In 2013, the Eastern population was delisted from the ESA, but retains its Depleted Status under the MMPA. Close monitoring will occur over the next few years to ensure that the change in its status will not endanger the population.
Population Trend: The majority of the Eastern DPS (Alaska, BC, Washington and Oregon) has increased at approximately 4% each year since 1979 through 2010, and pups have increased in all areas. Levels in California have declined from historic numbers, however the overall trend for the Eastern population is increasing.
The Western population appears to have stablized overall, and modeling indicates that counts have shown a slight increase between 1990 and 2012 east of Samalga Pass, while a decreasing trend West of Samalga Pass (the break between the Eastern and Central Aleutians).
Refs: Allen, B. M., and R. P. Angliss. 2013. Alaska Marine Mammal Stock Assessments, 2013. U.S. Dep. Commer., NOAA Tech. Memo. NMFSAFSC-277, 294 p.