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The Killer Whale (Orcinus orca), commonly referred to as the Orca and, less commonly, Blackfish, is the largest species of the dolphin family. They are found in all of the world's oceans, from the frigid Arctic and Antarctic regions to tropical seas. Killer Whales as a species have a diverse diet, although populations often specialize in particular types of prey. Some feed exclusively on fish, particularly salmon, and other populations hunt marine mammals such as sea lions, seals, walruses and even large whales. As they are known to be predators of large sharks, Killer Whales are regarded as the ocean's apex predator.
There are up to five distinct Killer Whale types distinguished by geographical range, preferred prey items and physical appearance. Some of these 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.
Killer Whales prey on diverse species. However, some populations specialize in particular prey species. For example, some populations in the Norwegian and Greenland sea specialize in herring and follow that fish's autumnal migration to the Norwegian coast. Other populations prey on seals. Field observations of northeast Pacific resident Killer Whales show that salmon accounted for 96% of their diet. 65% are the large, fatty Chinook. Chum salmon are also eaten, but smaler sockeye and pink salmon are not a significant food item. Depletion of specific prey species in an area is therefore cause for concern for local populations, despite the high diversity of prey. On average, a Killer Whale eats 227 kilograms (500 lb) each day. In 2008, the IUCN changed its assessment of the Killer Whale's conservation status from conservation dependent to data deficient, recognizing that one or more Killer Whale types may actually be separate, endangered species. Depletion of prey, pollution, conflicts with fishing, and habitat degradation are currently the most significant, worldwide threats.