[1] DNA analysis in 2007 estimated that the divergence point between the two sea lions took place around 2 million years ago (mya) in the early Pleistocene.

[4] Several taxidermied specimens can be found in Japan[5] and in the National Museum of Natural History, Leiden, the Netherlands, bought by Philipp Franz von Siebold.

[6] Male Japanese sea lions were dark grey, reaching lengths of 2.3 to 2.5 metres (7.5 to 8.2 ft) and weighed about 450 to 560 kilograms (990 to 1,230 lb).

Females were significantly smaller at 1.64 to 1.8 metres (5.4 to 5.9 ft) long and weighed about 120 kilograms (260 lb) with a lighter grey colour than the males.

[7] Japanese sea lions were found along the northwest Pacific coastline, specifically in Japan, Korea, southern Kamchatka Peninsula, and the Sakhalin Island.

The most recent sightings of Z. japonicus are from the 1970s, with the last confirmed record being a juvenile specimen captured in 1974 off the coast of Rebun Island, northern Hokkaido.

[20] The South Korean Ministry of Environment supports the effort because of the symbolism, national concern, the restoration of the ecological system, and possible ecotourism.

[19] Sightings of single sea lions of unclear identities have been reported at Iwami, Tottori in July 2003,[25] and on Koshikijima Islands in March 2016.