(Schreber, 1776) - Steller sea lion
Distinctive Characteristics
Steller sea lions are enormous and powerfully built. Aside from the overall large size of adults and generally robust build of all age and sex classes, the most conspicuous characteristics are the appearance of the head and muzzle, which are massive and wide. The eyes and ear pinnae appear small when compared with the size of the rest of the head. The vibrissae can be very long in adults. In all but adult males, there is little or no clear demarcation between the crown of the head and the muzzle, thus no forehead. In adult males, development of the sagittal crest produces a variable amount of forehead demarcating the muzzle and crown. Breeding bulls in their prime are very robust in the neck and shoulder area and have a mane of longer guard hairs. Both the fore- and hindflippers are very long and broad for an otariid. Collectively, these features make the upper body appear massive in relation to the lower body.
Coloration in adults is pale yellow to light tan above, darkening to brown and shading to rust below. Unlike most pinnipeds, when wet, Steller sea lions are paler, appearing greyish white. Pups are born with a thick blackish brown lanugo that is moulted by about 6 months of age. All ages and sexes have contrasting black flippers, naked except for a short stubble of dark fur partially covering the upper surface.
The dental formula is I 3/2, C 1/1, PC 5/5. There is a wide diastema (gap) between the fourth and fifth post-canines.
Can be confused with
The large robust bodies of Steller sea lions will allow them to be easily distinguished from the species of fur seals that inhabit their range. California sea lions are most likely to cause confusion. Careful attention to robustness, head and muzzle shape, coloration, and the size of bulls will allow them to be differentiated. Also, Steller sea lion bulls have much smaller, more posterior sagittal crests than those of California sea lion males.
Size
The maximum length of adult males is about 3.3 m and average weight is 1000 kg. The maximum length for adult females is about 2.5 m and average weight is 273 kg. Pups are born at an average of about 1 m and 18 to 22 kg.
Geographical Distribution
Steller sea lions are found from central California (formerly southern California), north to the Bering Sea, west along the Aleutian chain to the Kamchatka Peninsula, and south to northern Japan. Throughout their range they are primarily found from the coast to the outer continental shelf. However, they frequent deep oceanic waters in some parts of their range.
Biology and Behaviour
Steller sea lions breed in the late spring and summer. They are highly polygynous; adult males arrive before females and establish territories, which they aggressively and vociferously defend. Steller sea lions sometimes leave their haulouts in large groups of over 1000 individuals; however, sightings at sea are most often of groups of 1 to 12 animals. They aggregate in areas of prey abundance, particularly around fishing operations, such as trawlers and salmon driftnetters, where they feed on netted fish and bycatch. Steller sea lions feed on many varieties of fish and squid, with a decided preference for bottom species. Apparently, much feeding occurs at night.
Exploitation
Historically this sea lion was sporadically harvested for fat, meat, and “trimmings” (vibrissae and testes). There was a government-sponsored cull in this century that was pursued with the hope of limiting population size and its impact on commercially important fish species. Currently however, the Steller sea lion is suffering a massive range-wide population decline for, as yet, unknown reasons. The chief suspected cause is the over-exploitation of stocks of pollock in the high North Pacific. Other reasons suggested for the decline include long term change in ocean temperature, accumulation of human produced toxins, and disease. It may be that the decline is attributable to the subtle interaction of several of these factors. In 1990, the Steller sea lion was declared a threatened species under the United States Endangered Species Act.
IUCN Status
Vulnerable.