Carbon and nitrogen stable isotope ratios of the tissues and gut contents of a dugong from the temperate coast of Japan

Abstract

Okinawa Churaumi Aquarium, Ishikawa 424, Motobucho, Kunigamigun, Okinawa 905-0206, JapanThe dugong Dugong dugon is the only strictly marineherbivorous mammal. Dugongs are found as far north asJapan, but they have only been recorded off the coast ofOkinawa Island (26oN, 128oE) since 1970 (Marsh et al.2002).On 9 September 2002, an adult dugong was founddead on the Ushibuka coast (32oN, 130oE), of KyushuIsland (approximately 750 km north of Okinawa Island).It is of primary importance to establish whether thisdugong had inhabited the waters off Kyushu Island orwhether it had moved recently from a more southerlyregion such as Okinawa, because Okinawa is regarded asthe northern limit of the dugong’s habitat.Dugongs feed almost exclusively on various sea-grasses (Aketa and Kawamura 2001). Around OkinawaIsland, feeding trails of dugongs have only been found inseagrass beds (Marsh et al. 2002). At Ushibuka coast,however, macrophyte beds primarily contain macroalgae(Environment Agency 1989), not seagrasses.Naturally occurring stable isotopes of carbon andnitrogen have been used to study the foraging ecology ofseveral marine mammals (Bowen and Siniff 1999). Thenitrogen isotope ratio,