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Eumetopias jubatus ssp. jubatus 


Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Carnivora Otariidae

Scientific Name: Eumetopias jubatus ssp. jubatus
Species Authority: (Schreber, 1776)
Parent Species:
Common Name(s):
English Western Steller Sea Lion, Steller's Sea Lion, Steller Sea Lion, Northern Sea Lion
Taxonomic Notes: Until 2011, Steller Sea Lions were treated as a single taxon in IUCN Red List assessments. In the USA, the species was listed under the Endangered Species Act (ESA) in 1997 as two separate stocks (officially called “distinct population segments”) based on the phylogeographic method (Loughlin 1997). Although the strongest evidence for stock separation at the time was the distribution of mtDNA haplotypes across the range, a divergence in population trend was also apparent. Phillips et al. (2009) published a manuscript that argued for subspecies designation for the two stocks based on morphological and genetic studies. The Society for Marine Mammalogy subsequently recognized two subspecies of Eumetopias jubatus, E. j. jubatus (called the Western Steller Sea Lion) and E. j. monteriensis (called the Loughlin’s Steller Sea Lion; Committee on Taxonomy 2014). This assessment deals with the Western Steller Sea Lion.

Assessment Information [top]

Red List Category & Criteria: Endangered A2a ver 3.1
Year Published: 2016
Date Assessed: 2015-11-23
Assessor(s): Gelatt, T. & Sweeney, K.
Reviewer(s): Lowry, L.
Contributor(s): Lowell, F. & Burkanov, V.
Facilitator/Compiler(s): Lowry, L., Ahonen, H., Pollock, C.M., Chiozza, F. & Battistoni, A.
Western 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%/year. To date the causes of this and any remaining decline remain unknown, although some potential causes have been eliminated as likely threats to recovery. The Western Steller Sea Lion population reached its low point in approximately 2000, and since then in the U.S. has shown an annual increase of 1.81%. However this overall increase was the result of increases in abundance in the eastern Aleutian Islands and Gulf of Alaska, and persistent declines have continued in the western Aleutian and Commander Islands. As the rookeries in the declining areas continue to shrink, and in some cases disappear, their relative proportion of the total population has progressively less influence on the overall trend. The dramatic decline of the 1980s and 1990s still weights the trend such that the US portion of the western subspecies has experienced a population reduction of approximately 62% during the last three generations (NMFS 2008, Johnson and Fritz 2014). The abundance data from Russia are not as complete but when the most recent counts from 2013/2015 ( Burkanov et al. in press, Burkanov unpublished data) are combined with the count data for the US sites using the aggregated trend method in Johnson and Fritz (2014), the overall population decline for the last three generations is approximately 50%.  Western Steller Sea Lions should continue to be listed as Endangered under criterion A2a. The population reduction has been observed from count data and the causes are not understood. It is particularly concerning that the cause of the previous overall decline, and continued declines in some regions, have not been identified and that reports from 2013 in Russia indicate that an unexplained decline occurred at the Commander Islands, just west of the declining western Aleutians (Burkanov pers. comm.). If the decline continues in the western Aleutian Islands and Commander Islands, Western Steller Sea Lion rookeries could effectively disappear from a large region in the centre of the taxon’s range which will constitute a reduction in the area of occupancy.
Previously published Red List assessments:
  • 2012 – Endangered (EN)

Geographic Range [top]

Range Description:Western Steller Sea Lions (commonly described as the western distinct population segment; NMFS 2008), are found from the eastern Gulf of Alaska (144° W is the official eastern boundary), west along the Aleutian Islands to the Kamchatka Peninsula, and south along the Kuril Islands to northern Japan and the Sea of Japan. They also occur in the Sea of Okhotsk, the Kuril Islands, and the Bering Sea north to Bering Strait (Loughlin 2009). Vagrants have been recorded in China, and at Herschel Island in the Canadian Beaufort Sea.
Countries occurrence:
Japan; Russian Federation (Kamchatka, Kuril Is.); United States (Alaska, Aleutian Is.)
China; Korea, Democratic People's Republic of; Korea, Republic of
FAO Marine Fishing Areas:
Pacific – northeast; Pacific – northwest
Additional data:
Estimated area of occupancy (AOO) - km2:5938188Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:9179245
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Upper elevation limit (metres):5Lower depth limit (metres):427
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Abundance estimates of Steller Sea Lions in the US portion of the range are determined from counts from aerial photographs, and from researchers on land or in small boats. Pups and non-pups on rookeries and haulouts are counted during the pupping season. The National Marine Fisheries Service uses a Bayesian approach (agTrend; Johnson and Fritz 2014) to model all Steller Sea Lion survey data in the US range and to estimate the trends presented here. Counts in the Russian portion of the range are collected from shore or from small boats only.

Between 1977 and 2007 Western Steller Sea Lions declined by approximately 69% with the steepest drop occurring during 1985–1989 when the entire population decreased at a rate of 15% annually (Merrick et al. 1992). The US population reached its low point in approximately 2000, and between 2000 and 2015 the non-pup and pup counts within this portion of the range increased at average rates of 1.81%/year (95% interval of 0.98-2.61%) and 1.95%/year (95% interval of 1.35-2.55%) respectively. For the three generation time period used in this analysis (1985-2015) the US portion of the western stock declined by an estimated 62%. The Russian portion of the western stock, which constitutes all Steller Sea Lions in Russia, declined throughout the 1970s and 1980s and is believed to have reached the lowest abundance in the early 1990s at approximately 13,000 individuals (Burkanov and Loughlin 2005). Therefore, modeling the trend from 1985 to 2015 captures both a population decrease and an increase; for the period between the early 1990s (Burkanov and Loughlin 2005) and 2013-2015 (Burkanov et al. in press, Burkanov unpublished data) the Russian portion of the western stock has increased by 86%. The estimated size of the US portion of the western stock is 148,101 in 1985 (32,911 pups in 1985 estimated using agTrend multiplied by an extrapolation factor of 4.5 [Calkins and Pitcher 1982] to estimate the total abundance) and 55,791 (12,398 multiplied by the 4.5 extrapolation factor) in 2015.  In Russia, the last pup counts were in 2013 or 2015 (5,364 pups) which when multiplied by the same correction factor equates to 24,138 Sea Lions. The estimated reduction in abundance for the three-generation period from 1985 to 2015 is 62% in the USA and 50% for the Western subspecies overall.

The pattern of decline and recovery has not been the same in all parts of the Western Steller Sea Lion’s range. While the overall abundance in the USA and Russia has been slowly increasing in recent years, the number of animals in the western Aleutian Islands has continued to decline. In that region pup production is projected to have declined at a rate of 9.76% annually from 1985 to 2015. The overall amount of decline in the western Aleutians is over 81% from 1997 to 2015 and 94% from 1985 to 2015 (NMFS, unpublished data).

The most recent population viability analyses conducted using data collected from 1990 to 2012 for the Western Steller Sea Lion in US waters indicates a probability of quasi-extinction within 100 years of 0%. However, examining Sea Lions in the western Aleutian Island region alone revealed a 100-year extinction probability of approximately 89% (NMFS 2013).
Current Population Trend:Increasing
Additional data:
Number of mature individuals:40409Continuing decline of mature individuals:No
Extreme fluctuations:NoPopulation severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:

Steller Sea Lions are the largest otariids and the fourth largest pinniped. Both sexes are robust and powerfully built. They are sexually dimorphic, with adult males weighing three times as much as, and growing 20–25% longer than, adult females. Pups are born with a thick blackish-brown coat that is molted by about six months of age. The maximum length of adult males is about 3.3 m and average weight is 1,000 kg. The maximum length for adult females is about 2.5 m and average weight is 273 kg. Pups are born at an average size of about 1 m and 18–22 kg (Loughlin 2009).

The age of sexual maturity is 3–6 years for females, and 3–7 years for males (Calkins and Pitcher 1982). Males are not able to defend territories before they are nine years old. The annual pregnancy rate of mature females in the western population declined during the 1970s and 1980s and was estimated to be 55% in the 1980s based on collections of animals at sea (Pitcher et al. 1998). Age-structured modeling based on population counts from the central Gulf of Alaska indicates that the birth rate in 2004 was 36% lower than in the 1970s (Holmes et al. 2007). Gestation lasts one year, including a delayed implantation of about three months. Females may live to be up to 30 years old and males to about 20 years (Loughlin 2009). Life tables derived from collections made in the 1970s and 1980s (Calkins and Pitcher 1982), and other analyses (York 1994, Holmes and York 2003, Van de Kerk et al. 2013) indicate a generation time of approximately 10 years.

Steller Sea Lions are highly polygynous and breed in the late spring and summer. Adult males arrive at rookery sites before females and establish themselves on territories, which they aggressively defend. Pups are born from May through July, and females stay continuously ashore with their newborns for the first 7–10 days after giving birth. Following this period of attendance, females make foraging excursions for periods of 18–25 hours, followed by time ashore to nurse their pup. Females come into oestrus and mate about two weeks after giving birth. Weaning can occur before the next breeding season, but it is not unusual to see females nursing yearlings or older juveniles (Loughlin 2009).

Western Steller Sea Lions primarily haul out on rocky shores and forage in and around the outer continental shelf and slope. However, they frequent and cross deep oceanic waters in some parts of their range. They sometimes leave haulouts in very large groups but sightings at sea are most often of groups of 1–12 animals. They aggregate in areas of prey abundance, including near fishing vessels where they will feed on netted fish and discarded by-catch. Steller Sea Lions sometimes haul out on sea ice where it is available. They are not considered migratory but can move significant distances especially during the non-breeding years. Branded Western Steller Sea Lions are sometimes seen east of 144° W longitude, where they co-occur with Loughlin’s Steller Sea Lions. Jemison et al. (2013) reported that the young of both sexes in the western stock of Alaska venture into the eastern stock but that this is more common for females than males. Movements and diving behaviors of Steller Sea Lions vary among individuals, age classes, regions, and seasons (NMFS 2010). Overall, adults usually forage and use haul-out sites near their natal rookeries, where they typically return to breed. Adult females satellite-tagged in the US portion of the western subspecies range have been seen to take long pelagic foraging trips during winter, whereas their foraging range is more restricted during summer (Merrick and Loughlin 1997, Fadely and Lander 2012, Fadely et al. 2013). Adult females are capable of diving to depths at least 427 m but average approximately 45 m; dives are deeper during winter than summer (NMFS unpublished data). Dive duration is usually 2 minutes or less, but can exceed 13 min (Rehberg and Burns 2008). Dives of juveniles are generally shallow and short. Diving ability of pups increases with age (Loughlin et al. 2003, Fadely et al. 2005, Lander et al. 2010), with dives ranging on average from 5-35 m and up to 2 min (Loughlin et al. 2003, NMFS, unpublished data). The diving behavior of adult males has not been studied.

Western Steller Sea Lions feed on many types of fish and invertebrates. Much of the information on diet comes from Alaska, where they feed on Walleye Pollock, Pacific Cod, Atka Mackerel, Herring, Sand Lance, several species of flatfish, Salmon and Rockfish, and invertebrates such as Squid and Octopus (Sinclair and Zeppelin 2002, Sinclair et al. 2013). Food habits analysis using samples collected between 1990 and 2009 indicate that Western Steller Sea Lions in the USA consumed similar prey by region throughout the time period, but the distribution range of prey use increased over time (Sinclair et al. 2013). Adult females with young pups feed primarily at night, switching to foraging at any time of day after the breeding season. Steller Sea Lions are known to kill and consume young Northern Fur Seals at the Pribilof Islands (Gentry and Johnson 1981).

The primary predators of Steller Sea Lions are Killer Whales (Loughlin 2009). Sleeper Sharks have been suggested as a potential predator of juvenile Steller Sea Lions in the Gulf of Alaska (Horning and Mellish 2014) although previous work in the same area found that out of 198 Sharks examined near Steller Sea Lion rookeries during summer, none contained Sea Lion remains (Sigler et al. 2006). 

Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:No
Generation Length (years):10
Movement patterns:Not a Migrant
Congregatory:Congregatory (and dispersive)

Use and Trade [top]

Use and Trade: Western Steller Sea Lions have been harvested for commercial purposes in both the USA (Alaska) and the Soviet Union/Russia, but commercial harvesting ceased decades ago. They have been used as a subsistence resource by indigenous people for thousands of years. In the USA, Steller Sea Lions are primarily taken in communities in the northern Gulf of Alaska and Aleutian Islands (Haynes and Mishler 1991). The US Marine Mammal Protection Act allows Alaska Natives to take Steller Sea Lions for subsistence and creation of Native handicrafts. The most recent information on the Native Alaskan harvest from the western subspecies estimated take as 199/year during 2007-2011 (Allen and Angliss 2014). The Aleut communities on the largest Pribilof Island (Saint Paul) reported an average of 25 Steller Sea Lions taken annually during 1999-2015 including those struck and lost (St. Paul Tribal Council pers. comm.). Saint George Island reported an annual average of three Sea Lions killed during the period 2011-2015 (M. Williams pers. comm.).

Threats [top]

Major Threat(s): The reasons for the large declines in the Western Steller Sea Lion population are unclear, but they have been the subject of intensive and ongoing investigations. Deliberate killing by fishermen, disease, incidental take by fisheries, and reduced food supply have been suggested as factors that may have contributed to the decline (Lowry et al. 1989, Loughlin and York 2000) but there is no evidence to suggest that intentional killing of Sea Lions currently occurs at any level that could be limiting recovery. In 2008, the US National Marine Fisheries Service released a Recovery Plan that identified and ranked threats to recovery using a weight of evidence approach to assess the relative impact (NMFS 2008). They recognized three threats as “potentially high”: environmental variability, competition with commercial fisheries, and Killer Whale predation. Atkinson et al. (2008) reviewed the suspected anthropogenic sources of mortality for Western Steller Sea Lions and concluded that competition with fisheries and the potential impacts of contaminants could not be excluded as continuing threats to recovery.

Conservation Actions [top]

Conservation Actions: Western Steller Sea Lions are listed as vulnerable in the Threatened Wildlife of Japan Red Data Book. Hattori and Yamamura (2014) reported that over 200 Steller Sea Lions were culled annually during 1960-1993 to reduce predation on Japanese commercial fisheries. Recent work indicates that the annual culling was then reduced to a limit of 116/year until 2010 at which time a new 5 year quota of 1,030 culled Sea Lions was imposed. This resulted in an increased annual average take (Matsuda et al. 2015). In Russia, the major Steller Sea Lion rookeries were given protection under the Northern Fur Seal and Sea Otter Conservation Act in the late 1950s. They were listed as endangered (category 2) in the Russian Red Data Book in 1994 and harvest was prohibited. These measures had a positive effect in the western portion of the range as the population increased around Sakhalin Island, the Kuril Islands, and in the northern Sea of Okhotsk. However, abundance along the eastern coast of Kamchatka and in the Commander Islands has not recovered for unknown reasons (V. Burkanov pers. comm.). Unpublished data reported by V. Burkanov suggest that a decline in population on the Commander Islands occurred between 2013 and 2015.

In the US, the Steller Sea Lion is listed as depleted under the Marine Mammal Protection Act. The species (E. jubatus) was listed as threatened under the Endangered Species Act (ESA) in 1990, and in 1997 the western population (corresponding to E. j. jubatus) was uplisted to endangered. A recovery plan for Steller Sea Lions was approved in 1992, and a revised recovery plan was published in 2008. Critical habitat was designated in US waters under the ESA in 1993. A revision of critical habitat was initiated by the National Marine Fisheries Service in 2014 and was still underway in 2015. No-entry zones were established around rookeries at the time of ESA listing, and fisheries, particularly those operating in critical habitat, have been managed to reduce the likelihood of competitive interactions. Extensive funding has been made available for Steller Sea Lion research to develop information on ecology, behavior, genetics, population dynamics and movements. Results have been used to assist in the development of management activities, to attempt to understand the reasons for the decline, and to promote recovery of the species (NMFS 2008). The fact that the growth rate of the population is now positive suggests that at least some of these conservation efforts have had a beneficial effect.

Citation: Gelatt, T. & Sweeney, K. 2016. Eumetopias jubatus ssp. jubatus. The IUCN Red List of Threatened Species 2016: e.T17367725A66991984. . Downloaded on 30 June 2016.
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