Dugongs have very few natural predators. Their massive size, tough skin, dense bone structure, and rapidly clotting blood may aid defenses. Selachimorpha, Crocodyloidea, and Orcinus orca, however, feed on juvenile dugongs. Additionally, dugongs are often killed by Homo sapiens. The are hunted by some ethnic tribes in Australia and Malaysia, caught in gill and mesh nets set by fishers, struck by boats and ships, and are losing habitat and resources due to anthropogenic activities. ("Australian Government Great Barrier Reef Marine Park Authority", 2002; Anderson, 1984; Lawler et al., 2002; Marsh et al., 2002; Marsh, 2009; Wildscreen, 2003)