Steller Sea Lion

About the Species

The Steller (or northern) sea lion is the largest member of the family Otariidae, the “eared seals,” which includes all sea lions and fur seals. Steller sea lions are named for Georg Wilhelm Steller, the German surgeon and naturalist on the Bering expedition who first described and wrote about the species in 1742. While they are the only living member of their genus, they share parts of their range with a smaller related species, California sea lions. Steller sea lions' impressive low-frequency vocalizations sound more like roars than California sea lions’ barks. They also share parts of their range with another otariid: northern fur seal.

Historically, Steller sea lions were highly abundant throughout many parts of the North Pacific. Indigenous peoples and other settlers hunted them for their meat, hides, oil, and other products. In addition, they were killed for predator control and commercial harvests, causing their numbers to decrease. 

Steller sea lions were first listed under the Endangered Species Act in 1990. In 1997 NOAA Fisheries recognized two populations, classifying the eastern population as threatened and the western population as endangered. The eastern population has since recovered and is no longer listed, which is a significant achievement under the ESA. The western population remains endangered.

Learn more about the eastern and western populations of Steller sea lions

Status

The two populations of Steller sea lions represent different genetic, morphological, ecological, and population trends. We estimate population size in our stock assessment reports.

The western DPS includes all Steller sea lions originating from rookeries west of Cape Suckling (144° west longitude). The western stock of Steller sea lions decreased from an estimated 220,000 to 265,000 animals in the late 1970s to less than 50,000 in 2000. While the western population has been increasing slowly overall since about 2003, it is still declining quickly in large areas of its range.

The eastern DPS includes Steller sea lions originating from rookeries east of Cape Suckling. The eastern stock increased at a rate of 4.76 percent per year between 1989 and 2015, based on an analysis of pup counts in California, Oregon, British Columbia, and southeast Alaska.

Population trends for the eastern and western DPSs differ for complex reasons; most simply, the difference likely results from the different kinds and magnitudes of threats the species faces throughout its range.

Learn more about the eastern and western DPSs

Appearance

Steller sea lions are sexually dimorphic—adult males are much larger than females. Adult males may be up to 11 feet long and can weigh up to about 2,500 pounds. Adult females are 7.5 to 9.5 feet long and weigh up to about 800 pounds. This high level of dimorphism increases their vulnerability to disturbance when they are hauled out on land—large animals may crush smaller ones if they flee towards the water.

Adult males are further distinguished by long, coarse hair on the chest, shoulders, and back. An adult male’s chests and neck are also more massive and muscular than a female’s. Both adult males and females have light blonde to reddish brown coats that are slightly darker on the chest and abdomen. The light coloration is still visible when the body is wet. Like other pinnipeds, they molt, or shed their fur, every year.

Both sexes have long whitish whiskers (vibrissae) on their muzzles, which they use to sense prey and feel their way underwater. The flippers and other hairless parts of the skin are black. On land, sea lions, unlike "true" seals, can turn their hind flippers forward for walking. They can climb and are sometimes be found on rocks or cliff faces high above the water. When they swim, Steller sea lions use their back flippers to steer and their broader, longer front flippers to propel themselves.

Behavior and Diet

Steller sea lions are opportunistic predators, foraging and feeding primarily at night on over a hundred species of fish (including Atka mackerel, walleye pollock, salmon, cod, sand lance, arrowtooth flounder, Irish lords, rock sole, capelin, eulachon, Pacific sandfish, herring, rockfish, smooth lumpsucker, and hake) and cephalopods (including squid and octopus). Their primary prey diet varies in different parts of their range and at different times of the year, depending on the abundance and distribution of prey. To meet their energy requirements to grow, survive, and reproduce, Steller sea lions likely depend on predictable prey that are available in sufficient distribution and abundance to allow them to forage efficiently throughout the stages of their lives and during different times of the year. 

Steller sea lions forage near shore and in open waters. Different individuals may have different foraging strategies. For example, NOAA Fisheries’ research shows that in the non-breeding season, some adult females may spend long periods of time foraging well off the continental shelf while others forage much nearer to terrestrial sites. During the breeding season, a female must forage close enough to her rookery to return often and nurse her young. An adult female has very high energy demands—especially in the winter, when she must find enough food to feed herself and nurse her pup, possibly while pregnant with the next year’s pup. 

Steller sea lions, especially males, can travel long distances in a season. Diving ability changes with age. The deepest dive documented is about 1,400 feet in depth. 

Steller sea lions need undisturbed land habitat to rest, molt, socialize, mate, give birth, and nurse small pups during the breeding season. They are highly social and may rest in large groups, overlapping their bodies. At sea, they are seen alone or in small groups, but may gather in large "rafts" at the surface, including areas near important seasonal prey resources. Small pups learn to swim and begin to dive in nearshore waters near rookeries.

Where They Live

Steller sea lions prefer the colder temperate to subarctic waters of the North Pacific Ocean. They need both terrestrial and aquatic habitats. They mate and give birth on land, at traditional sites called rookeries. Haul-outs and rookeries usually consist of beaches (gravel, rocky, or sand), ledges, and rocky reefs. In the Bering Sea and Okhotsk Sea, sea lions may also haul out on sea ice.

Steller sea lions are distributed mainly around the coasts along the North Pacific Ocean rim from northern Hokkaido, Japan through the Kuril Islands and Okhotsk Sea, the Aleutian Islands and Bering Sea, the southern coast of Alaska, and south to central California. While they are most typically found in coastal waters on the continental shelf, they also occur and sometime forage in much deeper continental slope and pelagic waters, especially in the non-breeding season.   

The western DPS includes Steller sea lions that originate from rookeries west of 144° west longitude (Cape Suckling): those in the Gulf of Alaska, the Aleutian Islands, the Bering Sea, and Asia. The eastern DPS includes sea lions originating from rookeries in southeast Alaska, British Columbia, Washington, Oregon, and California. Data show that the foraging ranges of the two DPSs overlap, especially in the non-breeding season. For example, females from the eastern Gulf of Alaska regularly occur in parts of southeast Alaska and males from the eastern DPS have been observed as far north as the Bering Sea. In recent years, a “mixing zone” has also become established in northern southeast Alaska on at least two new rookeries partially established by western DPS females, who left their traditional rookeries during the period of sharp decline in the western population.

Learn more about the eastern and western populations of Steller sea lions

Lifespan & Reproduction

Steller sea lions are colonial breeders. They have a polygynous mating system, in which only a small proportion of the sexually mature males father most of the pups in a given season. 

Adult males, also known as bulls, arrive early on rookeries to establish breeding territories that they defend through the breeding season. Bulls become sexually mature between 3 and 8 years of age, but typically are not large enough to hold territory successfully until 9 or 10 years old. A mature male may go without eating for 1 to 2 months while it is aggressively defending his territory. 

Females begin to arrive on rookeries in mid-May. Females typically reproduce for the first time at 4 to 6 years of age, usually giving birth to a single pup each. They may not pup every year. Pupping occurs from about mid-May to mid-July and peaks in June. Females usually mate again within 2 weeks after giving birth. Sea lions are mammals; adult females, also known as cows, stay with their pups for a few days after birth before beginning a regular routine of foraging at sea, nursing pups on land, then going back to forage. Female Steller sea lions use smell and distinct vocalizations to recognize and create strong social bonds with their newborn pups. While most pups likely wean before their first birthdays, some pups are nursed for as long as three years.

At birth, pups are about 3 feet in length and weigh 35 to 50 pounds. Pups have a thick, dark brown to black "lanugo" coat until 4 to 6 months old, when they molt to a lighter brown. By the end of their second year, pups are the same color as adults. Males can live to be up to 20 years old, while females can live to be approximately 30.

Threats

Steller sea lions are exposed to a variety of human-caused and natural threats. Some of the most pressing ones are discussed below.

Learn more about additional threats to Steller sea lions

Effects of Fisheries on Prey 

Cumulative and annual commercial fishery removals may result in temporal and seasonal changes in distribution and abundance of primary prey, prey reduction, and  changes in prey size; they may also cause ecosystem effects. All of these may affect Steller sea lions’ ability to reliably access sufficient prey to sustain the health, reproduction, and survival of individuals and support sustained increase and eventual recovery of the population.  

Climate Change

Global climate change is expected to have profound impacts on arctic and sub-arctic marine ecosystems. This may affect the composition, spatial and temporal distribution, and abundance of prey available to Steller sea lions. 

Learn more about how sea level rise and ocean acidification may affect Steller sea lions

Predation

The primary predators of Steller sea lions are killer whales and humans. Sharks also prey on them in some locations. 

Toxic Substances

Contaminants enter ocean waters from many sources, such as oil and gas development, wastewater discharges, runoff, and other industrial processes. Once in the environment, these substances move up the food chain and accumulate in top predators. They can harm Steller sea lions’ immune and reproductive systems.

Learn more about this threat to Steller sea lions

Human-Caused Injuries

Steller sea lions may be disturbed by vessels approaching from the water, by aircraft, and by approach from the land. When disturbed, they may flee toward the water—sometimes in mass stampedes, during which pups and other smaller animals may be crushed or injured by larger ones. In addition, they can fall victim to retaliation (such as shooting) by frustrated boaters and fishermen.

Learn more about how illegal shooting can threaten Steller sea lions

Learn more about how disturbance can threaten Steller sea lions

Vessel Strikes

Inadvertent vessel strikes can injure or kill Steller sea lions. Vessel strikes are likeliest in areas where Steller sea lions are concentrated for feeding or rafting, or near large haulouts or rookeries from which large numbers of animals will be in transit.  

Entanglement

Entanglement and ingestion of fishing gear and marine debris is known to contribute to Steller sea lion injury and mortality. Steller sea lions can become entangled in fishing gear, either swimming off with the gear attached or becoming anchored. Once entangled, sea lions may drag and swim with attached gear for long distances, ultimately suffering fatigue, compromised feeding ability, or severe injury that may lead to reduced reproductive success and death. 

Current data indicate entanglement rates are greater in Southeast Alaska than in areas west of 144° west longitude. West of the regulatory boundary, entanglement is rarely observed during research cruises or reported by the public. However, not all entangled animals strand (e.g., they may drown) and not all stranded animals are found or reported. This is true especially in the most remote parts of the range of this species. 

Learn more about entanglement

Illegal Feeding

Feeding of sea lions is illegal and can lead to close interactios between humans and sea lions that pose risks to both. Feeding-related problems include changes in sea lion behavior; habituation; aggression toward humans; negative impacts to fisheries; and entanglement, injury, and death of animals.

Scientific Classification

Kingdom	Animalia
Phylum	Chordata
Class	Mammalia
Order	Carnivora
Family	Otariidae
Genus	Eumetopias
Species	jubatus