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.
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.
- Western DPS
- Eastern DPS
- Throughout Its Range
- Western DPS
- Western DPS
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.
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.
Steller sea lions are exposed to a variety of human-caused and natural threats. Some of the most pressing ones are discussed below.
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.
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.
The primary predators of Steller sea lions are killer whales and humans. Sharks also prey on them in some locations.
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.
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.
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 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.
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.
Eastern and Western Populations
The decline in the abundance of Steller sea lions was first observed in Alaska in the 1970s, and the rate of decline increased dramatically in the late 1980s. This decline prompted NOAA Fisheries to list the species range-wide as threatened in 1990. Due to genetic, morphological, ecological, and population trend data supporting the overall distinctiveness, NOAA Fisheries recognized two distinct population segments (DPS) in 1997.
The two recognized DPSs are:
- The western DPS, which includes all Steller sea lions originating from rookeries west of Cape Suckling (144° west longitude). The western DPS’s status was changed to endangered when it was established, due to continued declines; it remains endangered today.
- The eastern DPS, which includes Steller sea lions originating from rookeries east of Cape Suckling. The eastern DPS kept a status of threatened when it was established; by 2013, it had recovered enough for NOAA Fisheries to delist it.
Threats vary by DPS and throughout the range of each DPS. They also vary over time: some of the threats that led to Endangered Species Act listing are better controlled but new threats may be present or emerging.
While the western population has been increasing slowly overall since about 2003, it is still declining rapidly in large areas of its range, recent changes in vital rates in other areas are of high concern, and evidence as a whole indicates that there are multiple remaining threats to their existence.
Potential threats to the western DPS include:
- Direct and indirect effects of fisheries (competition for prey, changes to prey fields, incidental take, disturbance, ecosystem effects).
- Global climate change and other environmental variability.
- Changes to prey.
- Human disturbance.
- Predation in areas where sea lions are depleted.
- Environmental contaminants.
- Disease and parasites.
- Illegal shooting.
- Predation in areas where sea lions are depleted.
- Subsistence harvest.
- Illegal feeding.
- Vessel strikes.
Intentional killing, such as predator control and commercial harvests in large areas of the range of the eastern population, resulted in major reductions in abundance through much of the 1900s. There was also culling and commercial harvests in Alaska (before the protections of the Marine Mammal Protection Act), competition with fisheries for prey, incidental take in fisheries, possible entanglement of juveniles, legal and illegal shooting, and possibly other factors that adversely affected Steller sea lions. Intentional killing of Steller sea lions has not been permitted since the species was listed under the ESA in 1990, with exceptions to allow taking by a government official in select circumstances, non-wasteful taking by coastal Alaska Natives primarily for subsistence purposes and the making of handicrafts, and takes authorized under a marine mammal research permit.
Protections afforded the eastern DPS under the ESA (in the United States), and under laws in Canada, resulted in its recovery. The DPS no longer meets the definition of a threatened or endangered species under the ESA and, therefore, no longer requires the ESA’s protections. NOAA Fisheries’ analysis indicated that the overall abundance of the eastern DPS increased for more than 30 years. Further, NOAA Fisheries concluded that no threats put this DPS in danger of extinction now or in the foreseeable future throughout all or a significant part of its range. Accordingly, NOAA Fisheries delisted it—that is, removed ESA protections—in late 2013.
NOAA Fisheries may still monitor residual threats to the eastern DPS: threats that are reduced and contained enough that the species no longer meets the definition of threatened or endangered, but that are worth monitoring in case they reappear or become worse. Some of these threats are:
- Global climate change effects on prey, especially in the California Current Ecosystem.
- Indirect and direct fishery interactions.
- Ocean acidification.
- Environmental contaminants.
- Coastal development.
- Human disturbance.
- Oil and gas activity, including tankering and related threat of oil spills.
- Intentional killing.
- Harmful algal blooms.
Steller sea lions are also protected in Canada, where they are categorized as a Species of Special Concern, and they are listed as an endangered species under Russian legislation. While the Russian government currently has no organized program of monitoring and research, NOAA Fisheries has supported monitoring of population trends in Russia. In return, NOAA Fisheries has received high-value information needed to understand the overall status of the western population and threats to its long-term survival.
Steller sea lions are protected under both the Endangered Species Act and the Marine Mammal Protection Act. The western distinct population segment is listed as endangered under the ESA and, therefore, also designated as depleted under the MMPA. As a result, the stock is classified as a "strategic stock".
NOAA Fisheries has a responsibility under the ESA to take action to conserve Steller sea lions—that is, to use all methods and procedures that are necessary to bring the endangered western DPS to the point at which ESA protections are no longer necessary, and to sustain the eastern DPS’s recovery. NOAA Fisheries, state, international, university, tribal, other federal, and other scientists use a variety of innovative techniques to better understand Steller sea lion ecology and threats to their long-term viability. Working with our many partners, NOAA Fisheries scientists use this information to identify actions to remove or reduce threats.
The overall framework and priorities for research and management actions for the western population are described in the Steller Sea Lion Recovery Plan and modified, if needed, based on the best available scientific information. The framework and priorities for monitoring for the eastern population are described in the eastern DPS post-delisting monitoring plan.
Recovery Planning and Implementation
Under the ESA, NOAA Fisheries is required to develop and implement recovery plans for the conservation and survival of listed species.
NOAA Fisheries published the first recovery plan for the Steller sea lion in 1992. In 2008, NOAA Fisheries issued a revised recovery plan for both DPSs. These plans were developed with the assistance of recovery teams.
The 2008 Plan specifies:
- Site-specific management actions needed to achieve the plan’s goal for the conservation and survival of the species.
- Objective, measurable criteria for removing the species from the list, in accordance with the ESA.
- Estimates of the time and cost needed to carry out measures to achieve the plan’s goal and to reach intermediate steps toward that goal.
The Plan identifies major action categories related to the western DPS, aimed at achieving four broad goals:
- Ensure adequate habitat and range for recovery.
- Protect from overutilization for commercial, recreational, scientific, or educational purposes.
- Protect from diseases, contaminants, and predation.
- Protect from other natural or anthropogenic actions and administer the recovery program.
While the Plan identifies many specific recovery actions for the western DPS, it highlights four actions as especially important:
- Continue population modeling and research on the key threats potentially impeding sea lion recovery.
- Maintain current or equivalent level of fishery conservation measures.
- Design and implement an adaptive management program to evaluate fishery conservation measures.
- Develop an implementation plan.
For the eastern DPS, the Plan recommended that NOAA Fisheries conduct a status review to determine if the DPS should be delisted. This was accomplished and the eastern DPS was delisted in late 2013.
Together with our partners, NOAA Fisheries is undertaking numerous activities to support the goals of the Steller sea lion recovery plan, and to implement the many actions identified in it. Ultimately, we seek to have the species recover so the ESA’s protections are no longer needed to stave off its extinction.
Efforts to conserve Steller sea lions include:
- Implementation and enforcement of special prohibitions aimed at protecting the Steller sea lions and their rookeries.
- Protection against unauthorized take under the ESA and MMPA.
- Consultation with other federal agencies under Section 7 of the ESA to avoid jeopardy to the species and adverse modification or destruction of their designated critical habitat.
- Evaluation of actions seeking authorization of incidental take of Steller sea lions under the MMPA and identification of measures to mitigate impacts.
- Monitoring of incidental take of Steller sea lions in federal fisheries and estimation of total human-caused lethal take and serious injury.
- Collaboration with Alaska Native organizations to conserve Steller sea lions and provide for co-management of subsistence use by Alaska Natives. These activities have included collaborative exchanges of information, education, and outreach; collection of biological samples from harvested animals to further research into threats and status; monitoring of habitat use; harvest monitoring; and other activities.
- Education and outreach about regulations, laws, subsistence hunting, status, research, and threats.
- Protecting habitat and designating critical habitat.
- Reducing bycatch.
Critical Habitat Designation
Once a species is listed under the ESA, NOAA Fisheries evaluates and identifies whether any areas meet the definition of critical habitat. Those areas may be designated as critical habitat through a rulemaking process. The designation of an area as critical habitat does not create a closed area, marine protected area, refuge, wilderness reserve, preservation, or other conservation area; nor does the designation affect land ownership. Federal agencies that undertake, fund, or permit activities that may affect these designated critical habitat areas are required to consult with NOAA Fisheries to ensure that their actions do not adversely modify or destroy designated critical habitat.
In 1993, NOAA Fisheries designated critical habitat for Steller sea lions range-wide in the United States. This habitat includes: Alaska rookeries, major haulouts, and associated terrestrial, air, and aquatic zones; California and Oregon rookeries and associated areas; and three special aquatic foraging areas in Alaska. NOAA Fisheries is currently reviewing existing Steller sea lion critical habitat to take into account any new and pertinent sources of information since the 1993 designation, including the delisting of the eastern DPS.
View critical habitat maps for Steller sea lions:
- Alaska ESA Species and Critical Habitat Mapper Web Application
- Western-Southcentral Alaska (PDF, 1 page)
- Southeast Alaska (PDF, 1 page)
- West Coast data (shapefiles ZIP, 26K)
Conducting a 5-Year Review
In December 2017, NOAA Fisheries announced its intent to conduct a 5-year review of the endangered western DPS of Steller sea lion under the ESA. The ESA requires us to conduct these 5-year reviews to ensure that the listing classifications of species are accurate. The 5-year review must be based on the best scientific and commercial data available at the time of the review. We request submission of any such information on the western DPS of Steller sea lion, particularly information on the status, threats, and recovery of the species that has become available since the final listing determination in May 1997.
Implementing Measures to Protect Steller Sea Lions and Their Critical Habitat from Certain Groundfish Fisheries
The groundfish fisheries off Alaska target several species that are primary prey for Steller sea lions. These fisheries’ direct and indirect effects can harm Steller sea lions, as well as their critical habitat. After consultation under Section 7 of the ESA, NOAA Fisheries developed and implemented measures to avoid jeopardizing the continued existence of the western DPS and to avoid harming or destroying their designated critical habitat. These measures include restrictions on where and when specific commercial fisheries may operate, aimed at reducing their impact on Steller sea lions’ ability to meet their prey needs throughout the year and throughout their range. In addition to conserving prey for Steller sea lions, area closures reduce harm to prey habitats, harm to prey distribution patterns, the chance for the fisheries to disrupt important sea lion behaviors (e.g., pupping, nursing, breeding, resting, regulating temperature, and socializing) on or near their terrestrial habitat, the potential for stampedes or other disturbance-caused behaviors that may lead to death or injury, and the likelihood of incidental take. Literature also suggests that some protected zones may also have long-term positive impacts on ecosystem function. NOAA Fisheries has also imposed seasonal limits on the catch of certain Steller sea lion prey species and, in some cases, limits on catch of these specified species inside Steller sea lion critical habitat. There are also triggers in fishery management plans for additional protections when the estimated biomass of specified Steller sea lion prey species is extremely low.
As a minimum protective measure put in place at the time of listing, NOAA Fisheries implemented no-entry buffer zones around many of the rookeries in parts of the range now recognized as breeding habitat for the western DPS. While these protections serve several functions, they were designed in part to protect the species from being disturbed at their most sensitive sites. The current level of disturbance of sea lions at rookeries and haulouts is not known, and more information is needed about potential effects of repeated disturbance on the health, reproduction, and survival of Steller sea lions.
Protections Against Shooting
As a minimum protective measure at the time of listing, NOAA Fisheries implemented special protections against shooting. West of 144° west longitude, it is illegal to discharge a firearm at or within 100 yards of a Steller sea lion. This prohibition does not apply to coastal Alaska Natives when they are engaged in non-wasteful hunting of Steller sea lions primarily for subsistence.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings including seals and sea lions. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes identify strandings due to disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, and underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that may also have implications for human health and welfare.
Regulatory Actions & Documents
Initiation of 5-Year Review for the Endangered Western Distinct Population Segment of Steller Sea Lion
- Extension of Public Comment Period (83 FR 5248, 02/06/2018)
- Notice of Initiation of 5-Year Review/Request for Information (82 FR 57955, 12/08/2017)
Permit for Incidental Take of Western U.S. stock of Steller Sea Lions in Bering Sea and Aleutian Islands (BSAI) flatfish trawl, BSAI pollock trawl,
NOAA Fisheries conducts various research activities on the biology, behavior, and ecology of the Steller sea lion. The results of this research are used to inform management decisions and enhance recovery efforts for this endangered species.
Watch our video about how our scientists are investigating what’s going on with endangered Steller sea lions, learning why some populations of which are declining, while others are thriving.
Determining the number of Steller sea lions in each population—and whether a stock is increasing or decreasing over time—helps resource managers assess the success of enacted conservation measures. Our scientists collect information and present these data in annual stock assessment reports.
Our Alaska Fisheries Science Center is collaborating with the Alaska Department of Fish and Game and the Alaska Sea Life Center to collect observations of marked Steller sea lions for ongoing studies of life history and demography. By observing known-age individuals throughout their lives, scientists are able to calculate basic information such as age-specific survival, age of first reproduction, and reproductive rate—all of which are necessary to assess population recovery.
Ongoing research on abundance, movements and vital rates, and diet and foraging behavior helps us understand the role of Steller sea lions in the marine ecosystem and inform management decisions for the conservation of this important species.
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Data & Maps
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