The orca (Orcinus orca), also called killer whale, is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus Orcinus and is recognizable by its black-and-white patterned body. A cosmopolitan species, orcas can be found in all of the world's oceans in a variety of marine environments, from Arctic and Antarctic regions to tropical seas.

Orcas have a diverse diet, although individual populations often specialize in particular types of prey. Some feed exclusively on fish, while others hunt marine mammals such as seals and other species of dolphin. They have been known to attack baleen whale calves, and even adult whales. Orcas are apex predators, as they have no natural predators. They are highly social; some populations are composed of very stable matrilineal family groups (pods) which are the most stable of any animal species. Their sophisticated hunting techniques and vocal behaviours, which are often specific to a particular group and passed across generations, have been described as manifestations of animal culture.

The International Union for Conservation of Nature assesses the orca's conservation status as data deficient because of the likelihood that two or more orca types are separate species. Some local populations are considered threatened or endangered due to prey depletion, habitat loss, pollution (by PCBs), capture for marine mammal parks, and conflicts with human fisheries. In late 2005, the southern resident orcas, which swim in British Columbia and Washington waters, were placed on the U.S. Endangered Species list.

Wild orcas are not considered a threat to humans, and no fatal attack on humans has ever been documented. There have been cases of captive orcas killing or injuring their handlers at marine theme parks. Orcas feature strongly in the mythologies of indigenous cultures, and their reputation in different cultures ranges from being the souls of humans to merciless killers.

Naming Orcas are commonly referred to as "killer whales", despite being a type of dolphin.[6] Since the 1960s, the use of "orca" instead of "killer whale" has steadily grown in common use.

The genus name Orcinus means "of the kingdom of the dead", or "belonging to Orcus". Ancient Romans originally used orca (pl. orcae) for these animals, possibly borrowing Ancient Greek ὄρυξ (óryx). This word referred (among other things) to a whale species, perhaps a narwhal. As part of the family Delphinidae, the species is more closely related to other oceanic dolphins than to other whales

Types

The three to five types of orcas may be distinct enough to be considered different races, subspecies, or possibly even species. Although large variation in the ecological distinctiveness of different orca groups complicate simple differentiation into types, research off the west coast of North America has identified fish-eating "residents", mammal-eating "transients" and "offshores"

Other populations have not been as well studied, although specialized fish and mammal eating orcas have been distinguished elsewhere. Mammal-eating orcas in different regions were long thought likely to be closely related, but genetic testing has refuted this hypothesis.

Range and habitat

Orcas are found in all oceans and most seas. Due to their enormous range, numbers, and density, relative distribution is difficult to estimate, but they clearly prefer higher latitudes and coastal areas over pelagic environments. Areas which serve as major study sites for the species include the coasts of Iceland, Norway, the Valdes Peninsula of Argentina, the Crozet Islands, New Zealand and parts of the west coast of North America, from California to Alaska. Systematic surveys indicate the highest densities of orcas (>0.40 individuals per 100 km2) in the northeast Atlantic around the Norwegian coast, in the north Pacific along the Aleutian Islands, the Gulf of Alaska and in the Southern Ocean off much of the coast of Antarctica. They are considered "common" (0.20–0.40 individuals per 100 km2) in the eastern Pacific along the coasts of British Columbia, Washington and Oregon, in the North Atlantic Ocean around Iceland and the Faroe Islands.

In the Antarctic, orcas range up to the edge of the pack ice and are believed to venture into the denser pack ice, finding open leads much like beluga whales in the Arctic. However, orcas are merely seasonal visitors to Arctic waters, and do not approach the pack ice in the summer. With the rapid Arctic sea ice decline in the Hudson Strait, their range now extends deep into the northwest Atlantic. Occasionally, orcas swim into freshwater rivers. They have been documented 100 mi (160 km) up the Columbia River in the United States. They have also been found in the Fraser River in Canada and the Horikawa River in Japan.

Migration patterns are poorly understood. Each summer, the same individuals appear off the coasts of British Columbia and Washington. Despite decades of research, where these animals go for the rest of the year remains unknown. Transient pods have been sighted from southern Alaska to central California.

Feeding

Orcas are apex predators, meaning that they themselves have no natural predators. They are sometimes called "wolves of the sea", because they hunt in groups like wolf packs. Orcas hunt varied prey including fish, cephalopods, mammals, seabirds, and sea turtles. Different populations or ecotypes may specialize, and some can have a dramatic impact on prey species. However, whales in tropical areas appear to have more generalized diets due to lower food productivity. Orcas spend most of their time at shallow depths, but occasionally dive several hundred metres depending on their prey.

Behaviour

Day-to-day orca behaviour generally consists of foraging, travelling, resting and socializing. Orcas frequently engage in surface behaviour such as breaching (jumping completely out of the water) and tail-slapping. These activities may have a variety of purposes, such as courtship, communication, dislodging parasites, or play. Spyhopping is a behaviour in which a whale holds its head above water to view its surroundings. Resident orcas swim alongside porpoises and other dolphins.

Orcas will engage in surplus killing, that is, killing that is not designed to be for food. As an example, a BBC film crew witnessed orca in British Columbia playing with a male Steller sea lion to exhaustion, but not eating it.

Social structure

Orcas are notable for their complex societies. Only elephants and higher primates live in comparably complex social structures. Resident orcas in the eastern North Pacific live in particularly complex and stable social groups. Unlike any other known mammal social structure, resident whales live with their mothers for their entire lives. These family groups are based on matrilines consisting of the eldest female (matriarch) and her sons and daughters, and the descendants of her daughters, etc.

Like all cetaceans, orcas depend heavily on underwater sound for orientation, feeding, and communication. They produce three categories of sounds: clicks, whistles, and pulsed calls. Clicks are believed to be used primarily for navigation and discriminating prey and other objects in the surrounding environment, but are also commonly heard during social interactions.

Intelligence

Orcas have the second-heaviest brains among marine mammals. People who have interacted closely with orcas offer numerous anecdotes demonstrating the whales' curiosity, playfulness, and ability to solve problems. Alaskan orcas have not only learned how to steal fish from longlines, but have also overcome a variety of techniques designed to stop them, such as the use of unbaited lines as decoys.

In other anecdotes, researchers describe incidents in which wild orcas playfully tease humans by repeatedly moving objects the humans are trying to reach, or suddenly start to toss around a chunk of ice after a human throws a snowball.

The orca's use of dialects and the passing of other learned behaviours from generation to generation have been described as a form of animal culture.

Relationship with humans

The indigenous peoples of the Pacific Northwest Coast feature orcas throughout their art, history, spirituality and religion. The Haida regarded orcas as the most powerful animals in the ocean, and their mythology tells of orcas living in houses and towns under the sea. In Nuu-chah-nulth and Kwakwaka'wakw mythology, orcas may embody the souls of deceased chiefs. The Tlingit of southeastern Alaska regarded the orca as custodian of the sea and a benefactor of humans.

In the tales and beliefs of the Siberian Yupik people, orcas are said to appear as wolves in winter, and wolves as orcas in summer. The Ainu people of Hokkaido, the Kuril Islands, and southern Sakhalin often referred to orcas in their folklore and myth as Repun Kamuy (God of Sea/Offshore) to bring fortunes (whales) to the coasts, and there had been traditional funerals for stranded or deceased orcas akin to funerals for other animals such as brown bears.

"Killer" stereotype

In Western cultures, orcas were historically feared as dangerous, savage predators. Of the very few confirmed attacks on humans by wild orcas, none have been fatal. Unlike wild orcas, captive orcas have made nearly two dozen attacks on humans since the 1970s, some of which have been fatal. Competition with fishermen also led to orcas being regarded as pests. In the waters of the Pacific Northwest and Iceland, the shooting of orcas was accepted and even encouraged by governments.