Killer whale

Killer whale[1]
Temporal range: Miocene to recent [2]
Two killer whales jump above the sea surface, showing their black, white and grey colouration. The closer whale is upright and viewed from the side, while the other whale is arching backward to display its underside.
Transient killer whales near Unimak Island, eastern Aleutian Islands, Alaska
Diagram showing a killer whale and scuba diver from the side: The whale is about four times longer than a human, who is roughly as long as the whale's dorsal fin.
Size compared to an average human
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Class:Mammalia
Order:Artiodactyla
Infraorder:Cetacea
Family:Delphinidae
Genus:Orcinus
Fitzinger, 1860[4]
Species:O. orca
Binomial name
Orcinus orca
(Linnaeus, 1758)[5]
A world map shows killer whales are found throughout every ocean, except parts of the Arctic. They are also absent from the Black and Baltic Seas.
Orcinus orca range (in blue)
Synonyms

Orca gladiator

The killer whale or orca (Orcinus orca) is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. Killer whales 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 dolphins. They have been known to attack baleen whale calves, and even adult whales. Killer whales are apex predators, as there is no animal that preys on them. Killer whales are considered a cosmopolitan species, and can be found in each of the world's oceans in a variety of marine environments, from Arctic and Antarctic regions to tropical seas—killer whales are only absent from the Baltic and Black seas, and some areas of the Arctic Ocean.

Killer whales are highly social; some populations are composed of 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 killer whale 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 Killer Whales, the population that inhabits British Columbia and Washington state waters, were placed on the U.S. Endangered Species list.

Wild killer whales are not considered a threat to humans,[6] but there have been cases of captive orcas killing or injuring their handlers at marine theme parks. Killer whales feature strongly in the mythologies of indigenous cultures, with their reputation ranging from being the souls of humans to merciless killers.

Taxonomy and evolution

Orcinus citoniensis fossil, an extinct species of the same genus, Museo Capellini in Bologna
Modern orca skeleton, Naturalis Leiden.

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.[7] Konrad Gessner wrote the first scientific description of a killer whale in his Piscium & aquatilium animantium natura of 1558, part of the larger Historia animalium, based on examination of a dead stranded animal in the Bay of Greifswald that had attracted a great deal of local interest.[8]

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.[6] 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.[9]

Common names

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",[10] or "belonging to Orcus".[11] Ancient Romans originally applied orca (plural orcae) to these animals, possibly borrowing it from the Greek ὄρυξ, which referred (among other things) to a whale species. Since the 1960s, "orca" has steadily grown in popularity; both names are now used. The term "orca" is euphemistically preferred by some to avoid the negative connotations of "killer",[12] and because, being part of the family Delphinidae, the species is more closely related to other dolphins than to whales.[13]

According to some authors, the name killer whale is a mistranslation of the 18th century Spanish name asesina-ballenas which means literally whale killer.[14] Basque whalers would have given it such name after observing pods of orcas hunting baleen whales.

They are sometimes referred to as "blackfish", a name also used for other whale species. "Grampus" is a former name for the species, but is now seldom used. This meaning of "grampus" should not be confused with the genus Grampus, whose only member is Risso's dolphin.[15]

Types

The three to five types of killer whales may be distinct enough to be considered different races,[16] subspecies, or possibly even species[17] (see Species problem). The IUCN reported in 2008, "The taxonomy of this genus is clearly in need of review, and it is likely that O. orca will be split into a number of different species or at least subspecies over the next few years."[3] Although large variation in the ecological distinctiveness of different killer whale groups complicate simple differentiation into types,[18] research off the west coast of Canada and the United States in the 1970s and 1980s identified the following three types:

  • Resident: These are the most commonly sighted of the three populations in the coastal waters of the northeast Pacific. Residents' diets consist primarily of fish[19] and sometimes squid, and they live in complex and cohesive family groups called pods.[20] Female residents characteristically have rounded dorsal fin tips that terminate in a sharp corner.[21] They visit the same areas consistently. British Columbia and Washington resident populations are amongst the most intensively studied marine mammals anywhere in the world. Researchers have identified and named over 300 killer whales over the past 30 years.[22]
  • Transient: The diets of these whales consist almost exclusively of marine mammals.[19][21] Transients generally travel in small groups, usually of two to six animals, and have less persistent family bonds than residents.[23] Transients vocalize in less variable and less complex dialects.[24] Female transients are characterized by more triangular and pointed dorsal fins than those of residents.[21] The gray or white area around the dorsal fin, known as the "saddle patch", often contains some black colouring in residents. However, the saddle patches of transients are solid and uniformly gray.[21] Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California.[25] Transients are also referred to as Bigg's killer whale in honor of cetologist Michael Bigg. The term has become increasingly common and may eventually replace the transient label.[26]
  • Offshore: A third population of killer whales in the northeast Pacific was discovered in 1988, when a humpback whale researcher observed them in open water. As their name suggests, they travel far from shore and feed primarily on schooling fish.[27] However, because they have large, scarred and nicked dorsal fins resembling those of mammal-hunting transients, it may be that they also eat mammals and sharks.[28][29] They have mostly been encountered off the west coast of Vancouver Island and near Haida Gwaii. Offshores typically congregate in groups of 20–75, with occasional sightings of larger groups of up to 200.[30] Little is known about their habits, but they are genetically distinct from residents and transients. Offshores appear to be smaller than the others, and females are characterized by dorsal fin tips that are continuously rounded.[21]
Killer whale mother and calf extending their bodies above the water surface, from pectoral fins forward, with ice pack in background
Type C killer whales in the Ross Sea in the Southern Ocean: The eye patch slants forward.

Transients and residents live in the same areas, but avoid each other.[31][32][33] The name "transient" originated from the belief that these killer whales were outcasts from larger resident pods. Researchers later discovered transients are not born into resident pods. The evolutionary split between the two groups is believed to have begun two million years ago.[citation needed]

Other populations have not been as well studied, although specialized fish and mammal eating killer whales have been distinguished elsewhere.[34] In addition, separate populations of "generalist" (fish- and mammal-eating) and "specialist" (mammal-eating) killer whales have been identified off northwestern Europe.[35][36] As with residents and transients, the lifestyle of these whales appears to reflect their diet; fish-eating killer whales in Alaska[37] and Norway[38] have resident-like social structures, while mammal-eating killer whales in Argentina and the Crozet Islands behave more like transients.[39]

Three types have been documented in the Antarctic. Two dwarf species, named Orcinus nanus and Orcinus glacialis, were described during the 1980s by Soviet researchers, but most cetacean researchers are skeptical about their status, and linking these directly to the types described below is difficult.[17]

Some examples of variations in killer whales
  • Type A looks like a "typical" killer whale, a large, black and white form with a medium-sized white eye patch, living in open water and feeding mostly on minke whales.[17]
  • Type B is smaller than type A. It has a large white eye patch. Most of the dark parts of its body are medium gray instead of black, although it has a dark gray patch called a "dorsal cape"[40] stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. It feeds mostly on seals.[17]
  • Type C is the smallest type and lives in larger groups than the others. Its eye patch is distinctively slanted forwards, rather than parallel to the body axis. Like type B, it is primarily white and medium gray, with a dark gray dorsal cape and yellow-tinged patches. Its only observed prey is the Antarctic cod.[17]
  • Type D was identified based on photographs of a 1955 mass stranding in New Zealand and six at-sea sightings since 2004. The first video record of this type in life happened between the Kerguelen and Crozet Islands in 2014.[41] It is immediately recognizable by its extremely small white eye patch, narrower and shorter than usual dorsal fin, bulbous head (similar to a pilot whale), and smaller teeth.[42] Its geographic range appears to be circumglobal in subantarctic waters between latitudes 40°S and 60°S. And although nothing is known about the type D diet, it is suspected to include fish because groups have been photographed around longline vessels, where they reportedly prey on Patagonian toothfish (Dissostichus eleginoides).[43][44]

Types B and C live close to the ice pack, and diatoms in these waters may be responsible for the yellowish coloring of both types.[17][45] Mitochondrial DNA sequences support the theory that these are recently diverged separate species.[46] More recently, complete mitochondrial sequencing indicates the two Antarctic groups that eat seals and fish should be recognized as distinct species, as should the North Pacific transients, leaving the others as subspecies pending additional data.[47] Advanced methods that sequenced the entire mitochondrial genome revealed systematic differences in DNA between different populations.[48]

Mammal-eating killer whales were long thought likely to be closely related to other mammal-eating killer whales from different regions, but genetic testing refuted this hypothesis.[49]

The identified seven ecotypes inhabit isolated ecological niches. Of three orca ecotypes in the Antarctic, one preys on minke whales, the second on seals and penguins and the third on fish. Another ecotype lives in the eastern North Atlantic, while the three Northeast Pacific ecotypes are labeled the transient, resident and offshore populations, as discussed above. The research supported a proposal to reclassify the Antarctic seal- and fish-eating populations and the North Pacific transients as a distinct species, leaving the remaining ecotypes as subspecies. The first split in the orca population, between the North Pacific transients and the rest, occurred an estimated 700,000 years ago. Such a designation would mean that each new species becomes subject to separate conservation assessments.[48]

Other Languages
Afrikaans: Moordvis
العربية: حوت قاتل
asturianu: Orcinus orca
Avañe'ẽ: Pirachuguasu
azərbaycanca: Qatil balina
تۆرکجه: قاتیل ناققا
Bân-lâm-gú: Hó͘-keng
беларуская: Касатка
беларуская (тарашкевіца)‎: Касатка
български: Косатка
brezhoneg: Skoazog
català: Orca
Cebuano: Orcinus orca
čeština: Kosatka dravá
Cymraeg: Lleiddiad
davvisámegiella: Fahkon
Deutsch: Schwertwal
eesti: Mõõkvaal
Ελληνικά: Όρκα
español: Orcinus orca
Esperanto: Granda orcino
euskara: Orka
فارسی: نهنگ قاتل
føroyskt: Bóghvítuhvalur
français: Orque
Gaeilge: Cráin dhubh
galego: Candorca
客家語/Hak-kâ-ngî: Fú-kîn
한국어: 범고래
Հայերեն: Խոյադելֆին
hrvatski: Orka
Ido: Orko
Bahasa Indonesia: Paus pembunuh
interlingua: Orcinus orca
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᐋᕐᓗᒃ
Iñupiak: Aaġlu
íslenska: Háhyrningur
italiano: Orcinus orca
עברית: קטלן
kalaallisut: Aarluk
Latina: Orca
latviešu: Zobenvalis
lietuvių: Orka
Limburgs: Orka
македонски: Кит-убиец
Bahasa Melayu: Paus pembunuh
Nederlands: Orka
日本語: シャチ
norsk nynorsk: Spekkhoggar
Novial: Orcinus orca
occitan: Òrca
oʻzbekcha/ўзбекча: Kosatka
پنجابی: اورکا
português: Orca
română: Orcinus orca
sicilianu: Orca
Simple English: Killer whale
slovenčina: Kosatka dravá
slovenščina: Orka
српски / srpski: Кит убица
srpskohrvatski / српскохрватски: Orka
svenska: Späckhuggare
Tagalog: Orka
татарча/tatarça: Косатка
తెలుగు: ఓర్కా
Türkçe: Katil balina
українська: Косатка
Tiếng Việt: Cá voi sát thủ
Winaray: Orcinus orca
吴语: 杀人鲸
粵語: 殺人鯨
中文: 虎鯨