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Killer whales are large, active and intelligent. Males range from and weigh over , while females range from and weigh . The killer whale ("Orcinus orca") is the largest species of the Dolphin family. The species is found in all the world's oceans, from the frigid Arctic and Antarctic regions to warm, tropical seas. Killer whales are intelligent, versatile and opportunistic predators. Some populations feed mostly on fish, and other populations hunt marine mammals, including sea lions, seals, walruses, dolphins, large whales and some species of shark. They are considered an apex predator, as no animal predates on them. There are up to five distinct killer whale types, some of which may be separate races, subspecies or even species. Killer whales are highly social; some populations are composed of matrilineal family groups, which are the most stable of any animal species. The sophisticated social behavior, hunting techniques, and vocal behavior of killer whales have been described as manifestations of animal culture.