The killer whale or orca (Orcinus orca), less commonly, blackfish or seawolf, is the largest species of the dolphin family. It is found in all the world's oceans, from the frigid Arctic and Antarctic regions to warm, tropical seas. Killer whales are versatile and opportunistic predators. Some populations feed mostly on fish while other populations hunt marine mammals, including sea lions, seals, walruses and even large whales. They are considered the apex predator of the marine world, having no known predators. 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 culture.
Although the killer whale population as a whole is not considered to be an endangered species, some local populations are considered threatened or endangered due to depletion of prey species and habitat loss, pollution by PCBs, captures for marine mammal parks, and conflicts with vessels. In late 2007, the killer whales known as the "southern resident killer whales," were placed on the Endangered Species list.
Wild killer whales are usually not considered a threat to humans. There have, however, been isolated reports of captive killer whales attacking and, in at least one instance, killing their handlers at marine theme parks. There is also a level of confusion surrounding the term "whale". While killer whales are members of the dolphin family, they, and all other members of the dolphin family, are members of the sub-order Odontoceti and the order Cetacea, meaning "toothed whale" and "whale", respectively.