Investigation of the northern limit of dugong habitat in the Tokara Islands and Amami-Oshima in the Ryukyu archipelago, Japan

Abstract

To ascertain the northern limit of dugong habitat, this study investigated the distribution of dugong and seagrass in the Tokara Islands (Nakanoshima and Takarajima) and Amami-Oshima, in the Ryukyu archipelago. No dugong habitat and seagrass was found in Nakanoshima and Takarajima. In view of the seashore landscapes of the Tokara Islands, dugong habitat was not established from Kuchinoshima to Takarajima. Four dugong sightings occurred at Kurosaki and Yanosaki, in Kasari Bay at Amami-Oshima. The fact that that witnesses were a fisherman and a diver adds credibility to the sightings. In addition, colonies of three species of seagrass (Halophila ovalis, Syringodium isoetifolium and Halodule uninervis) were observed in Kasari Bay, distributed over a large area of the bay. These findings suggest that dugong habitat is established around Kusari Bay, and therefore, that this bay is the northern limit of dugong habitat in the Ryukyu archipelago.