The dugong, Dugong dugon, is found in offshore waters of the Red Sea, Indian Ocean, and W South Pacific Ocean. More strictly marine than the manatee, it seldom enters rivers. Its tail fin is crescent-shaped, and the male has long, tusklike incisor teeth. The male may reach a length of 12 ft (3.6 m) and weigh over 600 lb (270 kg). The dugongs' numbers have been depleted by hunting for its flesh, hides, tusks, and oil. The extinct Steller's sea cow was a large northern species that formerly inhabited the Bering Straits. It reached a length of 30 ft (9 m), weighed up to 4 tons (2,400 kg), and was insulated by very thick blubber. When it was discovered by Bering in 1741, the population was very small; within 30 years it was exterminated by hunting.
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