Dugongs have very few natural predators. Their massive size, tough skin, dense bone structure, and rapidly clotting blood may aid defenses. Sharks, crocodiles, and killer whales, however, feed on juvenile dugongs. Additionally, dugongs are often killed by humans. 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.