Appearance
The Steller sea lion is called “seevitchie” by the Aleuts and “sivuch” by the Russians, each translating to “seawolf.” The name that the animal now bears comes from George Wilhelm Steller, a naturalist aboard the 1741 Vitus Bering expeditions. Steller thought the creature resembled a lion because the male’s large neck and shoulder region look similar to the mane of a lion.
Steller sea lions, being otariids or eared seals, differ from the phocids, or “earless” seals, by having visible external ear flaps and long hind flippers that can be turned under, making travel on land easy. Steller sea lions are light tan to reddish brown in color. Males are visibly larger and appear lighter in color than females. Female sea lions average seven feet in length and about 600 pounds. Male sea lions, slightly longer at nine feet, weigh more than twice as much as females at an average of 1,500 pounds with “beach masters” reaching up to 2,400 pounds. Juveniles are chocolate brown in color and appear in early June. Pups stay dark for their first four to six months and then molt to a lighter color. Males are visibly larger and appear lighter in color than females. Juveniles are chocolate brown in color and appear in early June. Pups stay dark for their first four to six months and then molt to a lighter color.1
Range
Steller sea lions live in an arc around the north Pacific from central California to Japan. The animals seen in our area of Alaska are from the western stock. Steller sea lions do not migrate, but individuals disperse widely outside of breeding season. 1
Habitat
In early May, adult male sea lions haul out on established rookeries to claim their area. A returning bull will attempt to reclaim a spot he has held in past years. Eventually, he will be too old (between 13 to 15 years) to compete and will spend his retirement at a haul-out or possibly hold down some less desirable territory at the rookery edge. Haul-outs and rookeries are mostly located on remote and rocky coasts and islands with easy access to the open sea. 1
Feeding
Steller sea lions are opportunistic marine carnivores. Their most important prey species include: pollock, Atka mackerel, pacific herring, capelin, pacific sandlance, pacific cod, and salmon. Haul-outs and rookeries are mostly located on remote and rocky coasts and islands with easy access to the open sea. Steller sea lions often feed at night, but hunt schooling prey by day in large groups. It is believed that group feeding may help in controlling the movement of schooling fish and prey. 1
In the years 1976 and 1977, there was a warming period in the Gulf of Alaska waters. This warming lessened the availability of some of the sea lion’s prey, specifically oily fish like sandlance, white capelin, and herring. Sea lions now rely on pollock as a main dietary source. This diet switch may be a contributing factor in the decline of the sea lion as pollock lacks the oil critical to the maintenance of sea lion blubber. 1
Reproduction
Female Steller sea lions are sexually mature at four to six years of age. Bulls become mature at three to eight years, but cannot defend territory until they are nine or 10 years old. The competition for territory consists of aggressive displays: roaring, hissing, and chest-to-chest confrontations with open mouths that sometimes end in severe injury. The victor stays out of the water as long as months before any females visit him. Male sea lions fast during this time. 1
In late May or early June, female sea lions arrive at the rookery. Their main objective is to find a good beach on which to give birth. The male with the best birthing territory ends up with the most females. Just 10 to 14 days after giving birth, the female is ready to mate. After fertilization occurs, the embryo develops for a few weeks and then stops. After three to four months, in September or early October, the embryo implants in the uterine wall and resumes growing. This delayed implantation allows the pups to be born at an optimal time. Total gestation time is 11 and one half months. 1
Pups, usually one per female and weighing 35 to 50 pounds, are born mid-May to mid-July. For five to 13 days the mother stays with the pup; she then leaves the pup alone while she goes out to forage. At 10 to 14 days the pups form groups of their own—sleeping and playing together while the mothers forage. Pups are able to crawl and swim soon after birth but do not enter the water for about four to six weeks. The mother and pup find each other through scent and vocalizations. Pups will sometimes approach other females, but females will not accept pups that are not their own. A pup will continue nursing from the mother even after it starts foraging on its own. Some pups nurse until the mother’s next birth and some until they are three years old. 1
Conservation Status
In the 1960s, there were between 250,000 and 300,000 Steller sea lions worldwide. The Gulf of Alaska and Aleutian Islands historically contained the largest percentage of this population. In 1977, this area contained 74 percent of the global population, but by 1989 it dropped to 56 percent. In 1990, the Steller sea lion was listed as threatened throughout its range. Later studies of mitochondrial DNA from Steller sea lions suggest that there are at least two stocks, an eastern stock (California through Southeast Alaska) and a western stock (Prince William Sound and areas west). The decline was happening solely to the western stock and in 1997, the listing of the western stock was reclassified as endangered. 2
The International Union for Conservation of Nature and Natural Resources (ICUN), Red List Category & Criteria states that based upon current trends this species is declared near threatened. This assessment was made in June of 2012. This is a dramatic change from the 20 year downward trend in species numbers beginning in the late 1970s.
In explanation Steller sea lions experienced a dramatic and unexplained population decline of about 70% between the late 1970s and 1990 with the steepest decline occurring between 1985 and 1989 when the population was reduced by 15% per year. The population reached its low point in approximately 2000 and has shown an overall annual increase of 1.5–2% since that year. However, in the western Aleutian and Commander islands the trends have continued to show persistent declines. Overall, the Asian portion of the population declined through the 1990s and began to slowly increase in 2000 due to increases in the Sea of Okhotsk and the Kuril Islands. The decline of the 1980s and 1990s weights the trend such that the subspecies has experienced a population reduction of 57% during the last three generations (1981–2011), which qualified the species for Endangered. 5
References and Additional Information
- Write up by Kenai Fjord NP - https://www.nps.gov/kefj/naturescience/steller-sea-lion.htm
- https://www.nps.gov/kefj/naturescience/steller-sea-lion-decline.htm
- http://www.marinemammalcenter.org/education/marine-mammal-information/pinnipeds/steller-sea-lion/?
- http://en.wikipedia.org/wiki/Steller_sea_lion
- http://www.iucnredlist.org/details/8239/0
