Eumetopias jubatus ssp. jubatus

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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 Sea Lion, Steller Sealion, Northern Sea Lion, Steller's Sealion, Steller's Sea Lion, Northern Sealion
Taxonomic Notes: In previous IUCN evaluations, Steller Sea Lions have been treated as a single species. The species was listed as two separate stocks (officially called “distinct population segments”) under the United States Endangered Species Act (ESA) in 1997 based on the phylogeographic method (Loughlin 1997). Since that time, the stocks have been listed as endangered west of 144° W latitude, and threatened east of 144° W. 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. The two stocks have continued to display diverging trends, with continued increases in the east for at least 30 years and stability or slight increases in the west with localized areas of decline. In 2009, C. Phillips and co-authors (Phillips et al. 2009) published a manuscript that argued for sub-species designation for the two stocks based on morphological and genetic studies. The Society for Marine Mammalogy Ad-Hoc Committee on Taxonomy subsequently recognized two subspecies of Eumetopias jubatus, E. j. jubatus and E. j. monteriensis (Committee on Taxonomy 2012).

Assessment Information [top]

Red List Category & Criteria: Endangered A2a ver 3.1
Year Published: 2012
Date Assessed: 2012-06-05
Assessor(s): Gelatt, T. & Lowry, L.
Reviewer(s): Kovacs, K.M. & Burkanov, V.
Justification:

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 has shown an annual increase of 1.5–2% since that date. However, this overall increase has occurred despite persistent declines in the western Aleutian and Commander islands and was the result of increases in abundance in the eastern Aleutian Islands and Gulf of Alaska. 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 western stock has experienced a population reduction of approximately 57% during the last three generations (30 years, 1981–2011), qualifying as Endangered. It is particularly concerning that the cause of the previous overall decline, and continued declines in some regions, have not been identified. The continued decline for unknown reasons in the western Aleutian Islands of particular concern. If the decline continues E. j. jubatus rookeries will disappear from a large region in the centre of the taxon’s range which will constitute a reduction in AOO.

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) to the Aleutian Islands, west along the Aleutian Islands to the Kamchatka Peninsula, and from there 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 Beaufort Sea.
Countries:
Native:
Japan; Russian Federation (Kamchatka, Kuril Is.); United States (Alaska, Aleutian Is.)
Vagrant:
China; Korea, Democratic People's Republic of; Korea, Republic of
FAO Marine Fishing Areas:
Native:
Pacific – northeast; Pacific – northwest
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:

Between 1977 and 2007 Western Steller Sea Lions declined by approximately 69%. From 1981 to 2011 the decline was approximately 57%, with the steepest drop occurring during 1985–1989 when the population decreased at a rate of 15% annually. Total abundance in 2011 is estimated to be approximately 78,700 (National Marine Fisheries Service (NMFS), unpublished data). The decline was most dramatic (-81%) in the large populations from the Gulf of Alaska, west throughout the Aleutian Islands, and including Russia.

Several population viability analyses have been conducted for Steller Sea Lions (e.g., York et al. 1996, Gerber and Van Blaricom 2001, Winship and Trites 2006, NMFS 2008). Results have been consistent and have indicated that Western Steller Sea Lions had a high probability of declining to a low level with the most conservative of the analyses finding that the probability of quasi-extinction within 100 years was approximately 10% based on data from the 1970s through the late 1990s. Since 2000 the overall trend has been a slight increase of 1.5-2% per year. However, at western Aleutian Islands rookeries pup production declined at 9.2% per year during 1997-2011, and sea lion numbers on the largest rookery in the western Aleutian Islands dropped by over 50% between 2004 and 2011  (NMFS unpublished data).
Population Trend: Decreasing

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, and growing 20–25% longer than, adult females. Pups are born with a thick blackish-brown lanugo that is moulted 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 at sea (Pitcher et al. 1998). Recent age-structured modelling 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 delay of implantation of about three months. Females may live to be up to 30 years old and males to about 20 years (Loughlin 2009).

Steller Sea Lions are highly polygynous and breed in the late spring and summer. Adult males arrive before females and those that are nine years or older 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, primarily at night, 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 are primarily found from the coast, where they haul out on rocky shores, to the outer continental shelf and slope where the feed. 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; juveniles and subadults make the longest distance trips. Branded western Steller Sea Lions are sometimes seen east of 141° W longitude, where they co-occur with Loughlin’s Northern Sea Lions. Adults usually forage and live near their natal colonies and return to those sites to breed. The area used by adult females for foraging in winter is much greater than the area used in the summer, and females tend to dive deeper in winter than summer. Diving is generally to depths of 200 m or less and dive duration is usually two minutes or less, with both parameters varying by season and age of the animal. Diving ability of pups and juveniles increases with age, and as yearlings they routinely dive to depths of around 140 m for periods of two minutes (Loughlin et al. 2003, Rehberg and Burns 2008). The diving 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, octopus, bivalves and gastropods (Sinclair and Zeppelin 2002). 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, as well as Harbor and Ringed Seals.

The primary predators of Steller Sea Lions are Killer Whales (Loughlin 2009). Sleeper Sharks in Alaska have been found with Steller Sea Lion remains in their stomachs, but it is unknown whether the prey was killed or scavenged.

Systems: Terrestrial; Marine

Use and Trade [top]

Use and Trade: Steller Sea Lions have been important to the subsistence cultures of people living near them for long periods. Native Alaskans currently take about 300 a year for food and other products.

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). In the 2008 Recovery Plan the Steller Sea Lion Recovery Team 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 protected in the United States, Russia, and Japan. They have been listed in the Red Data Book of Japan as a rare species since 1993. An annual quota of 116 animals is allowed to be taken in Japanese waters for fishery nuisance control (Wada 1998). In Russia, the major Steller Sea Lion rookeries were protected under a 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 continued to decline for unknown reasons (V. Burkanov pers. comm.).

In the United States the Steller Sea Lion is listed as depleted under the U.S. Marine Mammal Protection Act. The species (E. jubatus) was listed as threatened under the 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 under the ESA in 1993. No-entry zones were established around rookeries at the time of 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, behaviour, 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.

Bibliography [top]

Atkinson, S., Demaster, D. P. and Calkins, D. G. 2008. Anthropogenic causes of the western Steller sea lion population decline and their threat to recovery. Mammal Review In Press(In Press): In Press.

Calkins, D. G. and Pitcher, K. W. 1982. Population assessment ecology and trophic relationships of Steller’s sea lions in the Gulf of Alaska. Environmental assessment of the Alaskan Continental shelf. U.S. Dept. of Commerce and U.S. Dept. of Interior, Final Reports of Principal Investigators, pp. 447-546.

Committee on Taxonomy. 2012. List of marine mammal species and subspecies. Available at: www.marinemammalscience.org. (Accessed: 7 May 2012.).

Gerber, L. R. and Van Blaricom, G. R. 2001. Implications of three viability models for the conservation status of the western population of Steller sea lions (Eumetopias jubatus). Biological Conservation 102: 261-269.

Holmes, E. E., Fritz, L. W., York, A. E. and Sweeney, K. 2007. Age-structured modeling reveals long-term declines in the natality of western Steller sea lions. Journal of Applied Ecology 17: 2214-2232.

IUCN. 2012. IUCN Red List of Threatened Species (ver. 2012.2). Available at: http://www.iucnredlist.org. (Accessed: 17 October 2012).

Loughlin, T.R. 1997. Using the phylogeographic method to identify Steller sea lion stocks. In: A. Dizon, S.J. Chivers and W.F. Perrin (eds), Molecular Genetics of Marine Mammals, pp. 159–171. Society for Marine Mammalogy Special Publication 3, Lawrence, Kansas, USA.

Loughlin, T.R. 2009. Steller sea lion Eumetopias jubatus. In: W.F. Perrin, B. Wursig and J.G.M. Thewissen (eds), Encyclopedia of Marine Mammals, pp. 1107-1110. Academic Press.

Loughlin, T. R. and York, A. E. 2000. An accounting of the sources of Steller sea lion, (Eumetopias jubatus), mortality. Marine Fisheries Review 62(4): 40-45.

Loughlin, T.R., Sterling, J.T., Merrick, R.L., Sease, J.L. and York, A.E. 2003. Immature Steller sea lion diving behavior. Fishery Bulletin 101: 566-582.

Lowry, L. F., Frost, K. J. and Loughlin, T. R. 1989. Importance of walleye pollock in the diets of marine mammals in the Gulf of Alaska and Bering Sea, and implications for fishery management. Proceedings of the International Symposium on the Biology and Management of Walleye Pollock, November, 1988. Anchorage, AK, U.S.A.: 710-726.

National Marine Fisheries Service. 2008. Recovery Plan for the Steller Sea Lion (Eumetopias jubatus). Revision. National Marine Fisheries Service, Silver Spring, Maryland, USA.

Phillips, C.D., Bickham, J.W., Patton, J.C. and Gelatt, T.S. 2009. Systematics of Steller sea lions (Eumetopias jubatus): subspecies recognition based on concordance of genetics and morphometrics. Occasional Papers, Museum of Texas Tech University 283: 1-15.

Pitcher, K.W., Calkins, D.G. and Pendleton, G.W. 1998. Reproductive performance of female Steller sea lions: an energetics-based reproductive strategy? Canadian Journal of Zoology 76: 2075-2083.

Rehberg, M.J. and Burns, J.M. 2008. Differences in diving and swimming behavior of pup and juvenile Steller sea lions (Eumetopias jubatus) in Alaska. Canadian Journal of Zoology 86: 539-553.

Sinclair, E. and Zeppelin, T. 2002. Seasonal and spatial differences in diet in the western stock of Steller sea lions (Eumetopias jubatus). Journal of Mammalogy 83.

Trites, A. W. and Donnelly, C. P. 2003. The decline of Steller seal lions Eumetopias jubatus in Alaska: a review of the nutritional stress hypothesis. Mammal Review 33(1): 3-28.

Wada, K. 1998. Steller sea lions: present status of studies of migratory ecology, and conflict between fisheries and conservation in Japan. Biosphere Conservation 1: 1-6.

Winship, A. J. and Trites, A. W. 2006. Risk of extirpation os Steller sea lions in the Gulf of Alaska and Aleutian Islands: A population viability analysis based on alternative hypotheses for why sea lions declined in western Alaska. Marine Mammal Science 22(1): 124-155.

York, A. E., Merrick, R. L. and Loughlin, T. R. 1996. An analysis of the Steller sea lion metapopulation in Alaska. In: D. R. McCullough (ed.), Metapopulations and wildlife conservation, Island Press, Washington, DC, USA and Covelo, CA, USA.


Citation: Gelatt, T. & Lowry, L. 2012. Eumetopias jubatus ssp. jubatus. In: The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 28 August 2014.
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