Orca Whale

Killer Whale - Oscines Orca

Orca Whale (Killer Whale) – Oscines Orca

“Orca” redirects here. For other uses, see Orca (disambiguation).

The killer whale (Orcinus orca), also referred to as the orca whale or orca, and less commonly as the blackfish or grampus, is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. Killer whales are found in all oceans, from Arctic and Antarctic regions to tropical seas. 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 like pinnipeds, and even large whales. They have been known to attack baleen whale calves. Killer whales are regarded as apex predators, lacking natural predators.

Killer whales are highly social; some populations are composed of matrilineal family groups which are the most stable of any animal species.[11] Their sophisticated hunting techniques and vocal behaviors, which are often specific to a particular group and passed across generations, have been anthropomorphically described as manifestations of culture.[12]

The IUCN currently 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 fisheries. In late 2005, the “southern resident” population of killer whales 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,[13] but there have been cases of captive orcas killing or injuring their handlers at marine theme parks.[14] Killer whales feature strongly in the mythologies of indigenous cultures, with their reputation ranging from being the souls of humans to merciless killers. 

Orcinus citoniensis fossil, an extinct species of the same genus, Museo Capellini in Bologna

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.[15] 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.[16]

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.[13]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.[17]

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”,[18] or “belonging to Orcus“.[19] 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”,[20] and because, being part of the family Delphinidae, the species is more closely related to other dolphins than to whales.[21]

According to some authors, the name killer whale would be a mistranslation of the 18th century Spanish name asesina de ballenas which means literally whale killer.[22] Basque whalers would have given it such name after observing pods of orcas hunting their own prey.

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 genus Grampus, whose only member is Risso’s dolphin.[23]

Types

The three to five types of killer whales may be distinct enough to be considered different races,[24] subspecies, or possibly even species.[25] 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.”[2] Although large variation in the ecological distinctiveness of different killer whale groups complicate simple differentiation into types,[26] 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[27] and sometimes squid, and they live in complex and cohesive family groups called pods.[28]Female residents characteristically have rounded dorsal fin tips that terminate in a sharp corner.[29] They visit the same areas consistently. British Columbia and Washington resident populations are amongst the most intensively studied marine mammals. Researchers have identified and named over 300 killer whales over the past 30 years.[30]
  • Transient: The diets of these whales consist almost exclusively of marine mammals.[27][29] Transients generally travel in small groups, usually of two to six animals, and have less persistent family bonds than residents.[31] Transients vocalize in less variable and less complex dialects.[32] Female transients are characterized by more triangular and pointed dorsal fins than those of residents.[29] 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.[29] Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California.[33] Transients are also referred to as Bigg’s killer whale in honor of Michael Bigg. The term has become increasingly common and may eventually replace the transient label.[34]
  • 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.[35]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.[36][37] 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.[38] Currently, 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.[29]

Transients and residents live in the same areas, but avoid each other.[39][40][41] 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.[42] Genetic data indicate the types have not interbred in the wild for up to 10,000 years.[43]

Other populations have not been as well studied, although specialized fish and mammal eating killer whales have been distinguished elsewhere.[44] In addition, separate populations of “generalist” (fish and mammal eating) and “specialist” (mammal eating) killer whales have been identified off northwestern Europe.[45][46] As with residents and transients, the lifestyle of these whales appears to reflect their diet; fish-eating killer whales in Alaska[47] and Norway[48] have resident-like social structures, while mammal-eating killer whales in Argentina and the Crozet Islands behave more like transients.[49]

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.[25]

  • 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.[25]
  • 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”[50] stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. It feeds mostly on seals.[25]
  • 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.[25]
  • 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.[51] 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.[52] 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).[53][54]

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.[25][55] Mitochondrial DNA sequences support the theory that these are recently diverged separate species.[56] 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.[57]

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.[58]

The identified seven ecotypes in 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. The research supported a proposal to reclassify the Antarctic seal- and fish-eating populations and the North Pacific transients, should be recognized as 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 enable/require that each new species be subject to separate conservation assessments.[59]

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