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Asesina de Ballenas (18th century Spanish)
Grampus (out of use)
50-60 (usual lifespan)
105 (oldest known)
|Reproduction||Sexual; give live birth|
Reach maturity at 15
|Average Weight||Males: 6 tonnes (5.9 long tons; 6.6 short tons)|
Females: 3 to 4 tonnes (3.0 to 3.9 long tons; 3.3 to 4.4 short tons)
|Average Length||Males: 20 to 26 ft (6 to 8 meters)|
Females: 16 to 23 ft (5 to 7 m)
|Prey||Varies by type|
|Related Species||Azerothian Orca|
|Possible Population||50,000 wild (56 captured as of 2016)|
The orca, also known as killer whales (Orcinus orca) is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. Orcas are found in all oceans, from Arctic and Antarctic regions to tropical seas. They 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. Orcas are apex predators, as there is no animal which preys on them.
As a species they are highly social animals; some populations are composed of matrilineal family groups (pods) which are the most stable of any animal species. Their sophisticated hunting techniques and vocal behaviors, which are often specific to a particular group and passed across generations, have been described as manifestations of animal culture.
The IUCN (International Union for the Conservation of Nature) 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 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.
Taxonomy and evolutionEdit
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. The orca 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.
The three to five types of killer whales may be distinct enough to be considered different races, subspecies, or possibly even species. 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." Although large variation in the ecological distinctiveness of different killer whale groups complicate simple differentiation into types, 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 and sometimes squid, and they live in complex and cohesive family groups called pods. Female residents characteristically have rounded dorsal fin tips that terminate in a sharp corner. 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.
- Transient: The diets of these whales consist almost exclusively of marine mammals. Transients generally travel in small groups, usually of two to six animals, and have less persistent family bonds than residents. Transients vocalize in less variable and less complex dialects. Female transients are characterized by more triangular and pointed dorsal fins than those of residents. 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. Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California. 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.
- 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. 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. 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. 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.
Transients and residents live in the same areas, but avoid each other. 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. Genetic data indicate the types have not interbred for up to 10,000 years.
Other populations have not been as well studied, although specialized fish and mammal eating killer whales have been distinguished elsewhere. In addition, separate populations of "generalist" (fish- and mammal-eating) and "specialist" (mammal-eating) killer whales have been identified off northwestern Europe. As with residents and transients, the lifestyle of these whales appears to reflect their diet; fish-eating killer whales in Alaska and Norway have resident-like social structures, while mammal-eating killer whales in Argentina and the Crozet Islands behave more like transients.
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.
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.
- 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" stretching back from its forehead to just behind its dorsal fin. The white areas are stained slightly yellow. It feeds mostly on seals.
- 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.
- 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. 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. 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).
Types B and C live close to the ice pack, and diatoms in these waters may be responsible for the yellowish colouring of both types. Mitochondrial DNA sequences support the theory that these are recently diverged separate species. 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. Advanced methods that sequenced the entire mitochondrial genome revealed systematic differences in DNA between different populations.
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.
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, 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.
While not studied thoroughly enough to confirm, multiple white orcas have been spotted in the waters surrounding Russia's Kuril Islands since around 2000 AD, which are thought to have gained their white hue due to Chediak-Higashi syndrome - a genetic disorder that causes albinism, though it also comes with increased vulnerability to respiratory infections and nervous system disturbances. This disorder was discovered in one white orca named Chimo; this captive orca however died at the age of 4.
These orcas may also be leucistic as opposed to being true albinos, which is instead a patchy white pigmentation. Either way this color scheme could cause them to have reduced heat absorption in the frigid waters they call home, lessened camouflage capabilities, high sensitivity to sunlight, and even hampered visual communicative abilities with other orcas.
It is currently believed that this potential albinism in orcas may be caused by being genetically passed to the next generation via inbreeding, which is a dangerous indication. While it is not clear why inbreeding may be occurring in the Kuril Islands pod, Human activity is always a candidate for blame: If too many females have been captured for aquarium showcasing or have been removed from the stock for any other reason, this will obviously jeopardize the entire group. The existence of between 5 and 8 were confirmed in the year 2016, only one is a fully mature adult - the 22-year-old male (as of 2016) named Iceberg. This indicates that while reaching maturity for white orcas may seem impossible, they are still capable of survival. In Iceberg's case, this may be due to his being a resident generalist orca; this means that he has remained with his mother and will for life, and as a fully-socialized cetacean he likely is more likely to survive.
Only 1 in every 10,000 orcas are completely white. They are so rare that despite the Southern Ocean of the Antarctic is a bastion for orca pods, Human researchers out in those waters may never see one themselves. However, Russian waters appear to be the world's number one area to see these creatures.