The Japanese sea lion was an aquatic mammal that became extinct in the 1970s and was to be found in the Japanese Archipelago and the Korean Peninsula. They inhabited the Sea of Japan along the northwest Pacific coastline, more specifically in Japan, Korea, southern Kamchatka Peninsula, Kuril Islands and the Sakhalin Island.
Prior to 2003, this species was considered to be a subspecies of the California sea lion. However, it was subsequently reclassified as a separate species. DNA analysis in 2007 estimated that the divergence point between the two sea lion species took place around two million years ago in the early Pleistocene epoch.
The male sea lions were dark grey and weighed about 500 kg reaching lengths of 2.4 metres. Females were significantly smaller at 1.6 metres and had a lighter colour. Female sea lions would give birth to one pup a year following a gestation period of nine months. Most of our knowledge about the Japanese sea lion comes from records. Bones have been excavated from shell middens from the Jōmon period in Japan (14500 BCE to 300 BCE). An 18th-century encyclopedia, Wakan Sansai Zue, states that the meat was not tasty and they were killed to provide oil for oil lamps.
Old Korean accounts also tell that this sea lion was found out at sea in the BoHai Sea, the Yellow Sea, and Sea of Japan. The Japanese sea lions are also remembered by the numerous places that carry their name all along the coast line of Japan. They usually came ashore on flat, open, sandy beaches and rarely in rocky areas. Their preference was to rest in caves.
It is estimated that 30,000 to 50,000 Japanese sea lions existed in the 19th century. Records from Japanese commercial fishermen in the early 20th century show that as many as 3,200 sea lions were caught or killed at the turn of the century. Overfishing caused catch numbers to fall drastically to 300 sea lions by 1915 and to a few dozen sea lions by the 1930s. There is a report of an individual being shot at Moneron Island in 1949.
Japanese commercial capture of Japanese sea lions ended in the 1940s after Japanese trawlers caught as many as 16,500 sea lions. This was the final blow that is thought to have caused their extinction. The last credible record of any number of wild Japanese sea lions was made in 1951 on the Liancourt Rocks in the Sea of Japan, reporting 50 to 60 animals. The very last sighting of this species was in 1974 when a juvenile sea lion was captured off the coast of Rebun Island, northern Hokkaido.
It is thought that in World War II Korean soldiers shot Japanese sea lions for target practice. Moreover submarine warfare during the war also caused severe damage to the sea lion’s habitat.
There are quite a few factors that lead to the extinction of this species. It is unlikely that they were widely hunted for food. In fact, there are plenty of written documents indicating that their meat had a terrible taste. Valuable oil was extracted from their skin and blubber. The sea lion’s internal organs were used to for oriental medicine. Its whiskers and skin were used as pipe cleaners and to make leather goods, a variety of clothing items and shoes as well as blankets. At the turn of the 20th century, they were also captured for use in circuses.
Japanese Sea Lions fed upon a variety of fish. The fishermen of the day considered them to be competition and as hindering their access to fish. That was another reason to kill them. The only known predators of the Japanese sea lion were humans.
There are striking similarities between the events that preceded the extinction of the Caribbean Monk Seal and those that preceded the extinction of the Japanese Sea Lion, although these two species lived 11,000 km apart – overkill, destruction of habitat and depletion of the animals’ food sources, all caused by humans. Another parallel is the zealous persecution of these animals by fishermen and hunters. In under one hundred years a population of around 40,000 Japanese sea lions was brought to nought. They were hunted relentlessly throughout their habitats and at all times during their life cycle. They simply could not live long enough, or reproduce fast enough, to survive.