Scientists in Japan are intrigued by evidence of river otters on Tsushima Island: the first confirmation of the animals in the country in almost four decades.

Exactly what sort of river otter, and whether it may have reached the Korea Strait isle from elsewhere, is unclear.

A camera trap set in Tsushima's mountains captured footage of the mustelid early in the morning of February 6, 2017. Researchers at the University of the Ryukyus, who installed the camera as part of a study on the island's native leopard cat (yamaneko), announced the discovery on August 17.

One rather thrilling possibility is that the video is of a Japanese river otter, last documented in 1979 in Kochi Prefecture and declared extinct by the Japanese Ministry of the Environment in 2012.

But researchers caution the critter may actually be a Eurasian river otter hailing from the Korean Peninsula – "a high chance", according to Masako Izawa of the University of the Ryukyus team, given that Tsushima Island lies about midway between Kyushu, the southernmost of Japan's main islands, and South Korea. A DNA analysis of otter scat discovered on Tsushima Island in July through a government survey suggested one of the scat-makers (for the droppings appeared to derive from two animals, possibly from different maternal lines) came from either South Korea or Russia's Sakhalin Island.


A professor at Chikushi Jogakuen University, Hiroshi Sasaki, told The Mainichi newspaper that it wouldn't be terribly difficult for river otters to reach Tsushima from the Asian mainland. "They are more than capable of swimming such a long distance," he said. "If riding ocean currents, it is completely within the realm of possibility for them to swim the 50 kilometres to Tsushima Island."

Another explanation, as Tokyo University of Agriculture assistant professor Daisuke Waku told the paper, is that the otter in the footage may have been an escaped or abandoned pet.

Adding to the confusion is the fact that taxonomists aren't entirely sure whether the Japanese river otter was a distinct species or simply a subspecies of the Eurasian river otter, as many contend. Otters once ranged across all the main islands of Japan, but heavy demand for their pelts, plus habitat modification and other human impacts, caused numbers to plunge beginning in the late 19th century.

The otter's apparent disappearance allied it with a number of unique Japanese representatives of Asian wildlife that went extinct in the 1800s and 1900s, including a variety of least horseshoe bat and two grey-wolf subspecies, the Hokkaido and Honshu wolves.

We may know more about the otter situation on Tsushima Island before too long. University of the Ryukyus researchers are planning to further investigate the footage they collected, according to The Asahi Shimbun, and the Ministry of the Environment hopes to track down fresher scat than the July samples, which could reveal more about the pedigree of any resident otters.



Top header image: Simon Willison/Flickr