Photo/Illutration A dugong is seen from an Asahi Shimbun helicopter off the Abu and Kayo districts of Nago, Okinawa Prefecture, in July 2010. (Asahi Shimbun file photo)

The dugong, an endangered marine animal species designated as a natural monument by the government of Japan, almost certainly inhabit broad areas of the Ryukyu Island chain in Okinawa Prefecture, researchers say.

The assessment was primarily based on DNA analysis of fecal matter, a relatively new field of study.

Researchers from Incorporated Foundation Okinawa Prefecture Environment Science Center, Ryukoku University as well as Kyoto University and other institutions, also confirmed the presence of dugongs in the Miyako Islands for the first time in about half a century.

However, the team members stressed that the population of dugongs in the region is extremely small, cautioning that their geographical distribution needs to be studied further. They called for measures to preserve seagrass beds, which serve as feeding grounds for the creatures.

The dugong, regarded as the inspiration for ancient seafaring tales of mermaids, is a mammal species that feeds mostly on seagrass.

The waters around Japan’s southwestern Nansei Islands, much part of which lie in Okinawa Prefecture, are believed to demarcate the northern limit of the dugong’s habitat areas in the Pacific.

The dugong population in the region, however, has been on the decline since the Meiji Era (1868-1912) due to overhunting for their fatty meat.

The International Union for Conservation of Nature and Natural Resources designated the dugong subpopulation in the Nansei Islands as being “critically endangered,” just one notch above being “extinct in the wild,” in its Red List in 2019.

Some experts suggest the species could have died out in the Nansei Islands due to a lack of sightings in the region after a dead female was found off Nakijin on the main Okinawa island in 2019.

However, an analysis of animal feces by members of the research team found DNA sequences that are specific to the dugong in waters off Irabujima island, which comes under the jurisdiction of Miyakojima, in June and August 2022, and off the Kushi district of Nago, on Okinawa’s main island, in July 2022.

That, combined with the geographical distribution of 66 dugong sightings and 26 feeding trails confirmed between 2010 and 2023, led the researchers to conclude that dugongs likely inhabit broad marine areas around the main Okinawa island as well as the Miyako Islands and Yaeyama Islands.

A feeding trail refers to a trail left in the bed of seagrass that a dugong has fed on.

However, there is an outside chance the dugongs are inhabitants of waters off northern Luzon Island in the Philippines that migrated to the Ryukyu Islands on the back of the Kuroshio current, the researchers added.

“Fecal DNA analysis is a new study method that provides more reliable scientific evidence than sightings and feeding trails,” said Hiroyuki Ozawa, head of Okinawa Prefecture Environment Science Center’s general environment research institute, who was part of the research team. “We hope to further specify the geographical distribution of dugongs to unravel their ecology.”

The research results were published in the journal Scientific Reports.

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