The animal that inspired seafarers to tell tales of mermaids is disappearing from the planet, according to a report released this week. The dugong, a large sea mammal that is a cousin to the famous manatee of Florida and the Caribbean, was thought by ancient sailors to be half-woman, half-fish, perhaps because of its habit of holding its young with one flipper when nursing. Because dugongs are highly sensitive to changes in their environment such as pollution and loss of food sources, they are the canaries in the mine of underwater habitats. According to the report, produced with funding from the U.N. Environment Programme and the World Conservation Union (IUCN), dugongs have already vanished in many places, and most populations are in decline.