A dugong, a rare marine mammal that inhabits waters around Okinawa, was spotted about 5 km east of Henoko on Sunday, the same day as seabed surveys started before landfill operations begin at the relocation site for the U.S. Marine Corps' Air Station Futenma.

A dugong, a threatened species due to the loss and degradation of underwater sea-grass meadows, was spotted and photographed from a helicopter by a Kyodo News reporter.

"There's no doubt this is a dugong," confirmed Mariko Abe of the Nature Conservation Society of Japan, who specializes in the area's ecosystem.

The dugong, a species of marine mammal which is believed to be the source of the mermaid and siren myths, was watched for about 10 minutes at around 4:25 p.m. when it repeatedly appeared at the surface and then dived.

The mammal's large nostrils on the muscular upper lip, which enable it to breathe when it surfaces, and its tail fluke were also visible.

In the Henoko coastal area, just a few kilometers away from where the mammal was spotted, a barge was readied Sunday. Around it, orange buoys and other floating devices have been installed to mark the restricted area where the survey of the seabed will be carried out.

Outside the marked-off area, as many as 15 Japan Coast Guard patrol ships were on duty in an effort to keep protesters away from the site.