Steller sea lions are the biggest of the eared seals (of the Otariidae family), a group including sea lions and fur seals. Male adults are two and a half times bigger than adult females and have large necks, with shoulders covered in a mane of coarse, long hair. The common name comes from George Wilhelm Steller, the German naturalist who in 1741 first described these seals. Eared seals can move their hind flippers independently, so they are particularly agile on land. Unlike true seals, this species swims using its fore flippers.
These sea lions inhabit the northern Californian coast, northwards to Alaska and on the coasts of Japan and Russia. They occur in the northern Pacific Ocean’s cool waters, hauling out on the rocky coastline and on beaches.
Steller sea lions are usually social and occur in large groups on beaches or in rookeries. They are usually in groups of two to twelve, but sometimes there are up to a hundred individuals together. At sea, they are solitary or in small groups. They forage at night near the shore and in pelagic waters. Steller sea lions can travel long distances during a season and are able to dive to about 1300 feet (400 m); however, they are not considered migratory. They use the land as haul-out sites to rest, molt, mate, and give birth. They produce powerful vocalizations accompanied, in males, by vertical head bobbing.
Steller sea lions are carnivores (piscivores, molluscivores), they mainly eat Atka mackerel, walleye pollock, Pacific cod, and Pacific salmon. They also eat octopus, squid, gastropods, and bivalves. They also kill harbor seals, ringed seals, younger northern fur seals, and other animals.
Steller sea lions use a polygynous mating system. The only males allowed to mate are the dominant males; however, younger males will sneak into rookeries and attempt to mate with the females without the dominant male noticing. The dominant males will guard and mate with as many as 30 females in one mating season. Females give birth to a single pup between mid-May and July after a gestation period that lasts for approximately 12 months. Females care for their offspring for up to three years, nursing them for as long as a year, sometimes longer. Males are not much involved in parental care but will guard all of the females they have mated with. Both males and females reach maturity between three to six years of age. Due to competition with other males, most bulls are unlikely to successfully breed until eight or ten years of age.
Current threats to this species include boat/ship strikes, illegal hunting/shooting, contaminants/pollutants, habitat degradation, offshore gas and oil exploration, interactions (indirect and direct) with fisheries, direct impacts largely because of fishing gear (set and drift gillnets, longlines, trawls, etc.) which can hook, entangle, injure, or kill them, and indirect impacts from competition for food, possible changes to critical habitat, etc.
According to the IUCN Red List, the total Steller sea lion population size is approximately 160,867 individuals. This includes population numbers of two recognized populations of the species: Western Steller sea lion population-79,929 individuals, with 55,791 animals in the USA and 24,138 animals in Russia; Loughlin’s Steller sea lion population-approximately 80,938 individuals. Currently, Steller sea lions are classified as Near Threatened (NT), however, their numbers today are increasing.
Due to their diet, Steller sea lions may have an influence on populations of fish, bivalves, gastropods, and cephalopods.