Killer whale

Appearance

A typical killer whale distinctively bears a black back, white chest and sides, and a white patch above and behind the eye.

Calves are born with a yellowish or orange tint, which fades to white. It has a heavy and robust body with a large dorsal fin up to 2 m tall. Behind the fin, it has a dark grey "saddle patch" across the back.

Antarctic killer whales may have pale grey to nearly white backs. Adult killer whales are very distinctive and are not usually confused with any other sea creature. When seen from a distance, juveniles can be confused with other cetacean species, such as the false killer whale or Risso's dolphin.

The killer whale's teeth are very strong and covered in enamel. Its jaws are a powerful gripping apparatus, as the upper teeth fall into the gaps between the lower teeth when the mouth is closed. The front teeth are inclined slightly forward and outward, thus allowing the killer whale to withstand powerful jerking movements from its prey while the middle and back teeth hold it firmly in place.

Killer whales are the largest extant members of the dolphin family. Males typically range from 6 to 8 metres long and weigh in excess of 6 tonnes. Females are smaller, generally ranging from 5 to 7 m and weighing about 3 to 4 tonnes.

The largest male killer whale on record was 9.8 m, weighing over 10 tonnes, while the largest female was 8.5 m, weighing 7.5 tonnes. Calves at birth weigh about 180 kg and are about 2.4 m long. The killer whale's large size and strength make it among the fastest marine mammals, able to reach speeds in excess of 30 knots.

The skeleton of the killer whale is of the typical delphinid structure, but is more robust. Its integument, unlike that of most other dolphin species, is characterised by a well-developed dermal layer with a dense network of fascicles of collagen fibers.

Killer whale pectoral fins are large and rounded, resembling paddles. Males have significantly larger pectoral fins than females. At about 1.8 m the male's dorsal fin is more than twice the size of the female's and is more of a triangular shape—a tall, elongated isosceles triangle—whereas hers is shorter and more curved.

Males and females also have different patterns of black and white skin in their genital areas. Sexual dimorphism is also apparent in the skull; adult males have longer lower jaws than females, and have larger occipital crests.

Killer whales have good eyesight above and below the water, excellent hearing, and a good sense of touch. They have exceptionally sophisticated echolocation abilities, detecting the location and characteristics of prey and other objects in their environments by emitting clicks and listening for echoes.

Naming

English-speaking scientists most often use the term "killer whale", although the term "orca" is increasingly used. Killer whale advocates point out it has a long heritage. Indeed, the genus name ''Orcinus'' means "of the kingdom of the dead", or "belonging to Orcus".

Ancient Romans originally applied ''orca'' to these animals, possibly borrowing it from the Greek, which referred to a whale species. Since the 1960s, orca has steadily grown in popularity; both names are now used. The term orca is preferred by some to avoid the negative connotations of "killer", and because, being part of the family Delphinidae, the species is more closely related to other dolphins than to whales.

They are sometimes referred to as blackfish, a name used for some whale species, as well. ''Grampus'' is a former name for the species, but is now seldom used. This meaning of grampus should not be confused with the ''Grampus'' genus, whose only member is Risso's dolphin.

Distribution

Worldwide population estimates are uncertain, but recent consensus suggests an absolute minimum of 50,000. Local estimates include roughly 25,000 in the Antarctic, 8,500 in the tropical Pacific, 2,250–2,700 off the cooler northeast Pacific and 500–1,500 off Norway. Japan's Fisheries Agency estimated 2,321 killer whales were in the seas around Japan.

Status

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 species, pollution, large-scale oil spills, and habitat disturbance caused by noise and conflicts with boats are currently the most significant worldwide threats.

Behavior

Female killer whales mature at around age 15. They then have periods of polyestrous cycling with noncycling periods of between three and 16 months.

Gestation varies from 15 to 18 months. Mothers calve, with usually a single offspring, about once every five years. In resident pods, births occur at any time of year, although winter is the most common.

Mortality is extremely high during the first six to seven months of life, when 37–50% of all calves die. Weaning begins at about 12 months and completes by the age of two.

According to observations in several regions, all male and female killer whale pod members participate in the care of the young. Killer and pilot whales are the only nonhuman species in which the females are known to go through menopause and live for decades after they have finished breeding. Killer whales are unique among cetaceans, as their heads become shorter as they age.

Females breed until age 40, meaning on average they raise five offspring. The lifespans of wild females average 50 years, with a maximum of 80–90 years.

Males sexually mature at the age of 15, but do not typically reproduce until age 21. Wild males live around 29 years on average, with a maximum of 50–60 years.

Day-to-day killer whale behavior generally consists of foraging, travelling, resting and socializing. Killer whales are frequently active at the surface, engaging in acrobatic behaviors such as breaching, spyhopping, and tail-slapping. These activities may have a variety of purposes, such as courtship, communication, dislodging parasites, or play. Spyhopping, a behaviour in which a whale holds its head above water, helps the animal view its surroundings.

Resident killer whales swim with porpoises, other dolphins, seals, and sea lions, which are common prey for transient killer whales.

Killer whales are notable for their complex societies. Only elephants and higher primates, such as humans, live in comparably complex social structures. Due to orcas' complex social bonds and society, many marine experts have concerns about how humane it is to keep these animals in captive situations.

Resident killer whales in the eastern North Pacific have a particularly complex and stable social grouping system. Unlike any other mammal species whose social structure is known, residents live with their mothers for their entire lives. These societies are based on matrilines consisting of the matriarch and her descendants which form part of the line, as do their descendants. The average size of a matriline is 5.5 animals.

Because females can reach age 90, as many as four generations travel together. These matrilineal groups are highly stable. Individuals separate for only a few hours at a time, to mate or forage. With one exception, the killer whale named Luna, no permanent separation of an individual from a resident matriline has been recorded.

Closely related matrilines form loose aggregations called pods, usually consisting of one to four matrilines. Unlike matrilines, pods may separate for weeks or months at a time. DNA testing indicates resident males nearly always mate with females from other pods.

Clans, the next level of resident social structure, are composed of pods with similar dialects, and common but older maternal heritage. Clan ranges overlap, mingling pods from different clans.

The final association layer, perhaps more arbitrarily defined than the familial groupings, is called the community, and is defined as a set of clans that regularly commingle. Clans within a community do not share vocal patterns.

Habitat

Killer whales are found in all oceans and most seas. Due to their enormous range, numbers, and density, distributional estimates are difficult to compare, but they clearly prefer higher latitudes and coastal areas over pelagic environments.

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. Resident killer whales sometimes travel as much as 160 km in a day, but may be seen in a general area for a month or more. Resident killer whale pod ranges vary from 320 to 1,300 kilometres.

Food

Killer whales hunt varied prey; however, different populations or species tend to specialize and some can have a dramatic impact on certain 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. Salmon account for 96% of northeast Pacific residents' diet. About 65% of them are large, fatty Chinook. Chum salmon are also eaten, but smaller 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 each day.

Because some killer whales prey on large whales and sharks, they are considered to be apex predators. They are sometimes called the wolves of the sea, because they hunt in groups like wolf packs.

Evolution

''Orcinus orca'' is the only recognized extant species in the genus ''Orcinus'', one of many animal species originally described by Linnaeus in 1758 in ''Systema Naturae''. Konrad Gessner wrote the first scientific description of a killer whale in his "Fish book" of 1558, based on examination of a dead stranded animal in the Bay of Greifswald that had attracted a great deal of local interest.

The killer whale is one of 35 species in the oceanic dolphin family, which first appeared about 11 million years ago. The killer whale lineage probably branched off shortly thereafter. Although it has morphological similarities with the pygmy killer whale, the false killer whale and the pilot whales, a study of cytochrome b gene sequences by Richard LeDuc indicated that its closest extant relatives are the snubfin dolphins of the genus ''Orcaella''.

Cultural

The indigenous peoples of the Pacific Northwest Coast feature killer whales throughout their history, art, spirituality and religion. The Haida regarded killer whales as the most powerful animals in the ocean, and their mythology tells of killer whales living in houses and towns under the sea. According to these myths, they took on human form when submerged, and humans who drowned went to live with them.

For the Kwakwaka'wakw, the killer whale was regarded as the ruler of the undersea world, with sea lions for slaves and dolphins for warriors. In Kwakwaka'wakw and Nuu-chah-nulth mythology, killer whales may embody the souls of deceased chiefs. The Tlingit of southeastern Alaska regarded the killer whale as custodian of the sea and a benefactor of humans.

The Maritime Archaic people of Newfoundland also had great respect for killer whales, as evidenced by stone carvings found in a 4,000-year-old burial site at the Port au Choix National Historic Site.

In the tales and beliefs of the Siberian Yupik people, killer whales are said to appear as wolves in winter, and wolves as killer whales in summer. Killer whales are believed to assist their hunters in driving walrus. Reverence is expressed in several forms: the boat represents the animal, and a wooden carving hung from the hunter's belt. Small sacrifices such as tobacco are strewn into the sea for them. Killer whales were believed to have helped the hunters even when in wolf guise, by forcing reindeer to allow themselves to be killed.