Japanese Sea Lion (Zalophus japonicus) is thought to have become extinct in the 1950s.
Prior to 2003 it was considered to be a subspecies of California Sea Lion as Zalophus californianus japonicus. However, it was subsequently reclassified as a separate species. Some taxonomists still consider it as a subspecies of the California Sea Lion. It has been argued that japonicus, californianus, and wollenbaeki are distinct species because of their distant habitation areas and behavioral differences.
They inhabited the Sea of Japan, especially around the coastal areas of the Japanese Archipelago and the Korean Peninsula. They generally bred on sandy beaches which were open and flat, but sometimes in rocky areas.
Currently, several stuffed specimens can be found in Japan and the National Museum of Natural History, Leiden, the Netherlands brought by Philipp Franz von Siebold. The British Museum possesses a pelt and 4 skull specimens.
Physical description
Male Japanese Sea Lions were dark grey and weighed up to 450 to 560 kg reaching lengths of 2.3 to 2.5 meters; these were larger than male California Sea Lions. Females were significantly smaller at 1.64 meters long with a lighter colour than the males. Their eyes are also very slanted compared to their North American counterparts.
Range and habitat
Japanese Sea Lions were primarily found in the Sea of Japan along the coastal areas of the Korean Peninsula, the mainlands of the Japanese Archipelago (the both sides on the Pacific Ocean and Sea of Japan), the Kuril islands, and southern tip of the Kamchatka Peninsula.
Old Korean accounts also describe that the sea lion and Spotted Seal (Phoca largha) were found in broad area containing the Bo Hai, the Yellow Sea, and Sea of Japan. The sea lions and seals left a lot of relevant place names all over the coast line of Japan such as Ashika-iwa (アシカ岩, sea lion rock) and Inubosaki point (犬吠崎, lit. dog-barking point) because of the similarity of their howls.
Lifestyle and reproduction
They usually bred on flat, open and sandy beaches but rarely in rocky areas. Their preference was to rest in caves.

Extinction
Harvest records from Japanese commercial fishermen in the early 1900s show that as many as 3,200 sea lions were harvested at the turn of the century and overfishing caused harvest numbers to fall drastically to 300 sea lions by 1915 and to few dozen sea lions by the 1930s. Commercial harvest of Japanese sea lions ended in the 1940s when the species became virtually extinct. In total, Japanese trawlers harvested as many as 16,500 sea lions, enough to cause their extinction, it is even believed that submarine warfare during World War II contributed to their habitat destruction. The last colony of sea lions was allegedly sighted by Korean coast guards in the 1950s and the last confirmed record of a Z. japonicus in Japan was a juvenile, captured in 1974 off the coast of Rebun Island, northern Hokkaido. Other unconfirmed sightings exist but it is possible these were, however, escaped Z. californianus seals.