Press Release on Discovery of River Otters in Tsushima

On 17th August (Thursday), Professor Masako Izawa of the Faculty of Science addressed members of the press at the press club room of the Ministry of Environment with regards to the discovery of otters in Tsushima.

The contents of Professor Izawa’s presentation are included in the following press release.

(Press Release)

Discovery of River Otters in Tsushima

Automatic photographing equipment that had been set up in Tsushima, Nagasaki prefecture for an ecological survey on Tsushima wildcats successfully captured images of river otters on February 6th, 2017. This discovery of river otters is the first time in 38 years that their existence in the wild has been confirmed in Japan.

Background of River Otters in Japan

River otters populated Japan up until the Meiji era, but extensive hunting for their skin and perceived medicinal properties, along with destruction of their habitats, forced their extinction between 1955 to 1960 from most regions of Japan apart from Shikoku. The remaining river otters in Shikoku were also thought to have become extinct in the decade between 1980 and 1990 (Ando, 2008, Sasaki, 2016).

There has also been evidence of records stating river otter inhabitation in Tsushima up until the Edo period.

River otters were last spotted in Kochi prefecture in 1979, and similar reports of their existence in the wild have not been recorded since then. In the fourth version of the Japanese Red Lists on nine taxonomic groups released by the Ministry of Environment in 2012, the Japanese river otter (Honshu south subspecies), Lutra Lutra nippon and the Japanese river otter (Hokkaido subspecies), Lutra Lutra whitelevi were classified as being extinct.

There remains some uncertainty regarding the taxonomic position of Japanese river otters. Mitochondrial genome analyses established that river otters native to the prefectures of Kanagawa and Kochi have a different bifurcation year from the Euroasian river otter, leading to the conclusion that they are genetically different from each other (Waku et al., 2016).

Regarding the River Otter Specimens that were Discovered in Tsushima

The type species of the specimens could not be successfully determined from existing video data. Their origins may be due to the three following possibilities.

  1. The river otters survived extinction by remaining in Tsushima.
  2. The river otters crossed into Japan by swimming across from Korea: expansion of distribution due to natural factors
  3. Migration from overseas due to human activity: expansion of distribution due to man-made factors

Ongoing Research Efforts

The Ministry of Environment has commenced a survey into river otter presence from this July by investigating traces of droppings and food remains. If the study uncovers evidence of fresh animal excretion, DNA samples can be taken to possibly determine the specimens’ type species and their origins. Outcomes of this investigative study are expected to be announced soon.

Requests Concerning the Survey on River Otter Inhabitation

The Ministry of Environment is currently conducting a study into the inhabitation status of river otters in Tsushima. To avoid the likelihood of disruption to the natural habitats of Tsushima wildcats and river otters, utmost cooperation to the following is requested.

  1. Do not provide food for the river otters.
    Leaving food may lure other wild animals such as Tsushima wildcats, as well as domesticated cats and stray dogs into the area. Intentional creation of spaces where many animals are likely to gather will create opportunities for infection caused by conflict and disease.
  2. Do not remove any river otter droppings from the study site.
    As this is a study into the inhabitation situation of river otters, the removal of otter excretion from their original site may negatively impact the outcomes of the study.


Genichi Ando. (2008) Nihon kawauso - zetsumetsu ni manabu hoken seibutsugaku. Tokyo: Tokyo Daigaku Shuppan-kai, 233pp.

Hiroshi Sasaki. (2016) Nihon no kawauso wa naze zetsumetsushitanoka. Tsukushi Jogakuen Daigaku Ningenbunkakennkyujo Nenpo 27:95-111.

Waku D, Segawa T, Yonezawa T, Akiyoshi A, Ishige T, Ueda M, et al. (2016) Evaluating the Phylogenetic Status of the Extinct Japanese Otter on the Basis of Mitochondrial Genome Analysis. PLoS ONE 11(3): e0149341. doi:10.1371/journal. pone.0149341.


Professor Masako Izawa, Biology Program Chemistry, Biology and Marine Science Faculty of Science, University of the Ryukyus 1 Senbaru, Nishihara, Okinawa 903-0213, Japan


Tel.: 090-4588-7054