Eumetopias jubatus (Schreber, 1776)
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publication ID |
https://doi.org/ 10.5281/zenodo.6604474 |
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DOI |
https://doi.org/10.5281/zenodo.6604429 |
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persistent identifier |
https://treatment.plazi.org/id/965C87FE-1E50-5642-991E-908F8D36F7EF |
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treatment provided by |
Diego |
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scientific name |
Eumetopias jubatus |
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Steller Sea Lion
Eumetopias jubatus View in CoL
French: Otarie de Steller / German: StellerSeelowe / Spanish: Ledn marino de Steller
Other common names: Northern Sea Lion, Steller's Sea Lion; Loughlin’s Northern Sea Lion (eastern population); Western Steller Sea Lion (western population)
Taxonomy. Phoca jubata Schreber, 1776 View in CoL ,
“Aufenthalt in dem nordlichen Theil des stillen Meeres...westlichen Kuste von America...ostlichen von Kamtschatka... Inseln... Kasten unter dem 56ten Grade der Breite liegen” (north part of the Pacific Ocean, Commander and Bering islands).
Although no subspecies of E. jubatus are recognized in the traditional taxonomy, there is agreement that there are at least two Distinct Population Segments (DPS’s), a Western and an Eastern, with a dividing line between them at 144° W in south-central Alaska. Two subspecies (jubatus for the western population and monteriensis for the eastern) were proposed in several papers that aligned with established DPS’s and are gaining support. Monotypic.
Distribution. N Pacific from C California N to Alaska and the Aleutian Is chain W to Bering Strait and Kamchatka, and S along the Kuril Is to N Japan, including Bering Sea, Sea of Okhotsk, and Sea ofJapan; occasionalvisitor to the Korean Peninsula and China. View Figure
Descriptive notes. Total length up to 330 cm (males) and 250 cm (females); weight 1000 kg, but up to 1120 kg (males) and 273 kg (females). Newborns are 100 cm and 18-22 kg. Dental formula I 3/2, C 1/1, PC 5/5 (x 2) = 34, with a diastema (gap) between the last upper post-canines. Steller Sea Lions are the largest of all otariids. Males and females are heavily built, and mature males have three times the weight of females and are 20-25% longer. Males have mane of guard hairs from head to shoulders and are very muscular in that area. Forehead of adult males is pronounced by sagittal crest on skull—a feature lacking in adult females and juveniles. Relative to massive heads of both sexes, eyes and ear pinnae appear small. Muzzle is thick and blunt, and pale vibrissae are long and prominent. Foreflippers and hindflippers are wide and long. Foreflippers have some hair on dorsal surfaces, but hair does not extend to rounded tips. Otherwise, flippers, including undersides, are covered with dark leathery skin. First digit is the longest and curves back. Cartilaginous rods in hindflippers lengthen toes, and first and fifth digits are longer than three middle digits. Similar to foreflippers, hindflippers have hair on upper part closest to body but otherwise are covered in dark leathery skin. Adults are tawny yellow to pale tan, with darker brown or reddish coloration on belly. When coat is wet, adult Steller Sea Lions appear quite pale, unlike most otariids that darken in water. Juveniles are darker than adults, ranging from dark buff to pale brown. Newborns are brownish-black until they molt after ¢.6 months. Scars are darker than the pale coat.
Habitat. Coastal waters to continental shelf and slope and traverse deeper pelagic zones. Steller Sea Lions will haul out on sea ice. They also enter bays and estuaries and will travel far up rivers in pursuit of anadromous fish. Favored terrestrial habitats are sandy and rock-strewn beaches and steep offshore rocks. In its marine habitats, the main predator is the Killer Whale (Orcinus orca), and great white sharks (Carcharodon carcharias) may be a danger. In Alaska, stomach contents of Pacific sleeper sharks (Somniosus pacificus) have included remains of Steller Sea Lions, which could have been from scavenging rather than direct attacks.
Food and Feeding. The diet of the Steller Sea Lion is composed of diverse fish and invertebrate species. In Alaska, they consume walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Atka mackerel (Pleurogrammus monopterygius), herring, sand lance ( Ammodytidae ), flatfish, salmon ( Salmonidae ), and rockfish ( Sebastidae ), along with squid, octopus, and mollusks. Lactating females forage mostly at night, but after the breeding season ends, they will feed day or night. Adult males prey on juvenile Northern Fur Seals ( Callorhinus ursinus ), Harbor Seals (Phoca vitulina), Ringed Seals (Pusa hispida), and possibly Sea Otters (Enhydra lutris).
Breeding. The Steller Sea Lion has the same general polygynous breeding system as described for the New Zealand Sea Lion ( Phocarctos hookeri ). For Steller Sea Lions, breeding season is in late spring and summer. Females mature at 3-6 years old. Adult males must be nine years old or more before they can establish territories, which they maintain through fighting, displays, and powerful deep roars, moving their heads up and down as they vocalize. Births occur in May-July. Female Steller Sea Lions remain with their newborns for 7-10 days after birth and then leave on foraging trips that are mainly nocturnal and last for 18-25 hours. Females enter estrus c.14 days after they give birth. Many young are weaned prior to the subsequent breeding season, but females may nurse yearlings, older offspring, and newborns at the same time. Gestation is c.12 months, including a delayed implantation of c¢.3 months. Usually, adult female otariids living in areas with good productivity have anywhere from a high 70% to a low 90% reproductive success rate, but annual pregnancy rate has declined and was estimated to be only 55% in the 1980s. Life span of the Steller Sea Lion is up to 30 years for females and c¢.20 years for males.
Activity patterns. At sea, Steller Sea Lions are most often seen singly or in small groups of 2-12 individuals. In eastern part of their distribution, they may travel with California Sea Lions ( Zalophus californianus ) and aggregate where prey is abundant. Diving abilities of adult male Steller Sea Lions are unknown, but females reach depths of up to 200 m during dives lasting two minutes or less, and they dive deeper in winter than summer. Yearlings can regularly dive to c.140 m.
Movements, Home range and Social organization. Steller Sea Lions are non-migratory, with adults generally feeding and living near their breeding rookeries, although immature individuals will undertake long distance trips. They are relatively sociable and may leave haul-outs simultaneously in large groups. In the eastern part of their distribution, they will often haul out with California Sea Lions and with Northern Fur Seals on the Pribilof Islands. Adult female Steller Sea Lions have a much larger foraging area in winter than summer. Vagrants have been found as far west as China and as far north as Herschel Island in the Beaufort Sea, and south to formerly used habitat in Southern California.
Status and Conservation. Classified as Near Threatened on The IUCN Red List. Two subspecies are listed on The IUCN Red List as Endangered (jubatus) and Least Concern (monteriensis). In the United States, the Western DPS is listed as endangered under the Endangered Species Act, and the Eastern DPS was recently delisted and considered recovered. Worldwide population of Steller Sea Lionsis estimated at 106,000-118,000 individuals, following a 64% decrease from 1960 to 1989. The decline has been most precipitous in the Western DPS, where numbers in the Aleutian Islands dropped by 81% and in Russia by 74%. This was at a time when the south-eastern Alaska population increased by 70%, causing overall numbers of Steller Sea Lions to increase slightly since 2000. Despite ongoing studies, reasons for decline in the past 50 years remain unclear. Proposed contributing factors are reductions in food resources because of commercial fishing, environmental changes, and increased hunting of Steller Sea Lions by Killer Whales. Steller Sea Lions are known to approach fishing vessels, and this behavior may have led to their being killed as bycatch in net fisheries in Alaskan waters. In the USA,critical habitat has been designated, including no-fishing and no-entry zones near rookeries. Although Steller Sea Lions are protected throughout most of their distribution, Native Alaskans are allowed to harvest 150-300 individials/ year for food and traditional uses.
Bibliography. Atkinson, Calkins et al. (2008), Atkinson, DeMaster & Calkins (2008), Berta & Churchill (2012), Burkanov & Loughlin (2005), Fritz & Hinckley (2005), Gelatt & Lowry (2008b), Gerber & VanBlaricom (2001), Hattori et al. (2009), Holmes et al. (2007), Hoover (1988), Jefferson et al. (2008), Kaplan et al. (2008), Loughlin (2009), Loughlin & York (2000), Loughlin, Perez & Merrick (1987), Loughlin, Perlov & Vladimirov (1992), Loughlin, Rugh & Fiscus (1984), Maniscalco et al. (2010), Merrick et al. (1994), NMFS (2008), Phillips, Bickham et al. (2009), Phillips, Gelatt et al. (2011), Pitcher & Calkins (1981), Raum-Suryan et al. (2002), Reijnders et al. (1993), Rice (1998), Rosen &Trites (2000), Schusterman (1981), Sease & York (2003), Sinclair & Zeppelin (2002), Trites & Donnelly (2003), Trites et al. (2007), Winship & Trites (2006).
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