A wild river otter was caught on film on Tsushima island, Nagasaki Prefecture, in February for the first time in Japan in 38 years, it was announced on Aug. 17.
The sighting was made public by Masako Izawa of the Animal Ecology Laboratory at the University of the Ryukyus in Okinawa Prefecture. While Izawa did not rule out the possibility of the otter being a Japanese river otter -- a species declared extinct -- she also pointed out, "There is a high chance that the otter is simply a Eurasian otter that swam the roughly 50 kilometers of ocean from the Korean Peninsula."
Izawa and her research team had set up a camera in the mountains on the island to conduct an ecological survey of the Tsushima leopard cat. At 4:20 a.m. on Feb. 6, 2017, the camera captured five seconds of footage of the otter. The last time a Japanese river otter was filmed in the wild was in Susaki, Kochi Prefecture, in 1979. The Ministry of the Environment declared the species extinct in 2012.
According to the Environment Ministry, seven samples of otter excrement were found on Tsushima island in a follow-up government survey conducted from July 11-18. Analyzing DNA from two of the samples, it became clear that there are at least two otters on the island. One of the animals appears to be from South Korea or Russia's Sakhalin Island, but since the samples appeared to be roughly one to two months old, the ministry was unable to confirm if the droppings came from a Japanese river otter or a Eurasian otter.
"We'd like to find fresher samples by expanding the range of our survey," a representative from the environment ministry team said. With a fresher sample, it is said to be possible to also determine the sex of the otter.
Chikushi Jogakuen University professor Hiroshi Sasaki, who is helping with the environment ministry survey, echoed Izawa's theory that there is a high probability the otters are Eurasian otters from South Korea.
"There are some Eurasian otters living on islands as far as 30 kilometers from the Korean Peninsula," he said. "The DNA sampled was the same, so it appears as though they both came from continental Asia. They are more than capable of swimming such a long distance. If riding ocean currents, it is completely within the realm of possibility for them to swim the 50 kilometers to Tsushima island."
Daisuke Waku, an assistant professor at Tokyo University of Agriculture who also saw the footage, agreed with Sasaki. "From the face and body shape as well as its movements, there is no doubt that the animal is a river otter. Otters can't swim distances of tens of kilometers all at once, but all the gathered evidence points to the possibility that the otters have swum from the Korean Peninsula," he said. "There is also the possibility of it being a Eurasian otter kept as a pet that escaped or was abandoned."
Under the Convention on International Trade in Endangered Species of Wild Fauna and Flora, the import and export of Eurasian otters is strictly prohibited. However, there are said to be cases of the animal being smuggled. In addition, the small clawed otter, native to regions including Southeast Asia, can be imported with the permission of the exporting government.
The Japanese islands from Hokkaido to Kyushu were once the habitat of the Japanese river otter, but the animals were hunted for their fur, and the destruction of their habitat led to a decrease in numbers. There are records of otters on Tsushima island from the Edo period, but even the possibility of those otters being Eurasian otters cannot be ruled out.