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. Killer whales are regarded as an apex predator as they have no natural predators.
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 and vocal behaviour of killer whales have been described as manifestations of culture.
The IUCN currently assesses the conservation status of the killer whale as data deficient because of the likelihood that one or more killer whale types could actually be a separate species in need of protection. Some local populations are considered threatened or endangered due to depletion of prey species, habitat loss, pollution by PCBs, historic capture for marine mammal parks, and conflicts with fisheries. In late 2005, the killer whales known as the "southern resident killer whales" were placed on the U.S. Endangered Species list.
Wild killer whales are not considered a threat to humans, although there have been cases of captive killer whales attacking their handlers at marine theme parks. The killer whale features strongly in the mythologies of indigenous cultures. In Western cultures, it has had a reputation for being a fearsome predator, but in recent decades better understanding has led to widespread appreciation of the species.