The Japanese sea lion is considered by many authors to be extinct. It was long considered a subspecies of the California sea lion. Very little information exists on the appearance of this animal. In an account from otter and seal hunters working in this area in the early 20th century, the “black sea lion” was said to have been present in addition to animals referable to Steller sea lions. This common name may usefully point-out that some animals, presumably adult males, as is the case for many adult male California sea lions, were black. A color plate showed, and an accompanying account from the text of a mid-19th century work gave, a description of the animal as “straw colored with a darker throat and chest in the female.”
A Japanese zoologist interviewed in the 1950s gave the lengths of adult males as 2.5 m and adult females as 1.4 m, and reported a four-month-old pup as being 65 cm long and 9 kg. A review in the late 1950s listed eight specimens as existing in museums, with none of these in Japan. No photographs were found for use in the preparation of this account.
People traveling in the former range of this species should be vigilant, and record detailed notes for any otariid sightings that cannot be readily identified as Steller sea lions or northern fur seals. For field identification purposes, features available for California and Galapagos sea lions should be presumed to be similar, and may be consulted until such time as additional information about this species can be uncovered or extensive searches can provide strong evidence of it being extinct.
Can be Confused With
Japanese sea lions shared their range with Steller sea lions and northern fur seals. Operating under the assumption that Japanese sea lions were similar to California sea lions, the following is extracted from the California sea lion account and may be helpful in separating Japanese sea lions from Steller sea lions and northern fur seals.
Juvenile, subadult, and small adult female Steller sea lions fall within the size range of California sea lions. Careful attention to head and muzzle size and shape, overall coloration, and length and width of fore and hind flippers permits differentiation. Smaller Steller sea lions in the size range of large California sea lions will look like they are more muscular and powerfully built than similar-sized California sea lions, which look more filled-out with fat and streamlined. Also, smaller Steller sea lions have little or no sagittal crest development and a nearly flat-topped head whereas comparably-sized adult and subadult California sea lion males have a moderate to large sagittal crest and more pronounced forehead. Steller sea lion eyes also seem smaller and set farther apart due to the proportionately larger head and wider muzzle.
Northern fur seals have thick pelage and look shaggier than the more sleek California sea lion. Males are dark gray to charcoal, or dark brown in color, often with light tips to the long hairs on the mane, which impart a grizzled grayish cast to the dark pelage. Adult females, juveniles and subadults are multicolored with dark gray or brown on the dorsal surface, and have tan to buff ventral coloration, with a variable pale band across the chest. They have a short muzzle and sharply pointed face. The ears are proportionately longer and stand out farther from the head when the animal is in the water or otherwise wet. Adult and older subadult northern fur seals have long white conspicuous vibrissae.
Northern fur seals have very long rear flippers with long cartilaginous extensions, all of equal length and width. The fur on the dorsal surface of the fore flippers stops abruptly at the wrist line, or bend point in the flipper, and when wet the flipper has a smooth “clean shaven look” when compared with a California sea lion which has fur on the top of the flipper extending in a “V” beyond the wrist. At sea, northern fur seals actively groom while resting at the surface, and will sleep in a “jug-handle” position.
Japanese sea lions were found from the southern end of Japan, north through the Korea Strait and throughout the Sea of Japan to Sakhalin Island, and on both sides of Kamchatka from the eastern Sea of Okhotsk, and the western North Pacific, south through the Kuril Island archipelago to the southern end of Japan.
Ecology and Behavior
Very little information is available on these animals, although they are assumed to be similar to the California sea lion. They are said to be good divers, although dive depths have never been measured directly.
Feeding and Prey
It is said that they fed on fishes, but not much other information is available.
Threats and Status
This species is probably extinct. A comprehensive survey and study has not yet been undertaken to determine the status of the species, and search for specimens, accounts, data, and photographs in Japan, South and North Korea, and Russia. The last estimates available were of 100 animals on Takeshima Island and a total population of up to 300 in the late 1950s. Estimates are that 30,000 to 50,000 animals may have been present in the mid-19th century and that the population was decimated by heavy hunting pressure. The species probably became extinct shortly after the last reports of sightings in the late 1950s, although the remote possibility of a remnant colony in poorly-studied Korean waters still exists.
Heath, C.B. 2002. California, Galapagos, and Japanese sea lions Zalophus californianus, Z. wollebaeki, and Z. japonicus. pp. 180-186 in W.F. Perrin, B. Würsig and J.G.M. Thiewissen (eds.), Encyclopedia of Marine Mammals. Academic Press.
King, J.E. 1961. Notes on the Pinnipeds from Japan described by Temminck in 1844. Zoologische Mededelingen 37(13):211-224.
Nakamura, K. 1997. Status of the Japanese sea lion, Zalophus californianus japonicus (Peters, 1866), its past and present. International Marine Biological Research Institute, Kamogawa, Japan 7:131-137. (Japanese with English abstract and figure captions).
Nishiwaki, M. and F. Nagasaki. 1960. Seals of the Japanese coastal waters. Mammalia 24:459-467.
Nishiwaki, M. 1973. Status of the Japanese sea lion. pp. 80-81 in Seals. IUCN supplemental paper Number 39. International Union for the Conservation of Nature.
Odell, D.K. 1981. California sea lion - Zalophus californianus Lesson, 1828. pp. 67-97 in S.H. Ridgway and R.J. Harrison (eds.), Handbook of Marine Mammals, Vol. 1: The walrus, sea lions, fur seals and sea otter. Academic Press.
Scheffer, V.B. 1958. Seals, sea lions and walruses a review of the Pinnipedia. Stanford University Press. 179 pp.