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Orcinus orca (Linnaeus, 1758)

provided by EG-BAMM, Ryan Reisinger & Bob Pitman

Description

Killer whales are among the oceans’ most iconic species. Their large size, striking appearance, complex social structure and top predator status give them great charisma. They are the apex predators in marine ecosystems and, as a species, have an incredibly varied diet. Considered among the most widely distributed non-human mammals on the planet, killer whales occur throughout the world’s oceans.
Killer whales (or orcas) are toothed whales (odontocetes) and the largest members of the dolphin family (Delphinidae). They are currently recognized as a single species - Orcinus orca - but various populations show consistent differences in morphology, foraging behaviour, social organization, vocal behaviour and genetic structure. The differences are so large that in some cases these ‘ecotypes’ are proposed to be different species. Currently, 5 distinct types are recognised in the Southern Ocean:
1) Type A killer whale

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2) Large type B or pack ice killer whale
3) Small type B or Gerlache killer whale
4) Type C or Ross Sea killer whale
5) Type D or Subantarctic killer whale

Species details

Photos

  • Orcinus orca -  -
  • Orcinus orca - A killer whale spyhops at the Prince Edward Islands - Ryan Reisinger
  • Orcinus orca - An adult female killer whale, with her calf at her side, attacks a southern elephant seal at the Prince Edward Islands - Ryan Reisinger
  • Orcinus orca - Scale illustration of various types of killer whales - Uko Gorter
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Species distribution

Killer whales are the most cosmopolitan cetacean and can be found in any marine region. They are most abundant, however, at higher latitudes and on continental shelves and margins, i.e., areas of high marine productivity. In the Southern Ocean, type A killer whales have a circumpolar distribution and occur mostly in open water, seaward of the pack ice. Pack ice killer whales also occur around the entire continent, mainly among the pack ice, and Gerlache killer whales have been recorded only in the Antarctic Peninsula region. Ross Sea killer whales are known only from East Antarctica where they occur deep in the pack ice; they are absent from the Antarctic Peninsula area. Subantarctic killer whales seem to occur in open water and around subantarctic islands. They have been recorded between 40° and 60°S and probably have a circumpolar distribution. Killer whales have been recorded at most subantarctic islands. Photo-identification studies of killer whales at the Crozet Islands and the Prince Edward Islands have shown that the same individuals regularly return to these islands. Some inter-archipelago movement has been recorded. Various migrations have been proposed for Antarctic killer whales, particularly seasonal movements to lower latitudes during winter, but winter sightings in the pack ice of type B (pack ice or Gerlache) and Ross Sea killer whales show that at least some animals remain at high latitudes in the winter. Scars on type A, both type B and Ross Sea killer whales from bites of cookiecutter sharks (Isistius spp.) – which occur only in tropical and warmer subtropical waters – as well as sightings indicate movement to lower latitudes. This has been confirmed by satellite tracking of pack ice killer whales which revealed rapid movement from the Antarctic Peninsula to subtropical waters and back. Type A killer whales have not been identified around the sea ice during winter (although little winter work has been conducted). Killer whales at subantarctic islands are most abundant during the summer breeding seasons of their seal and penguin prey, and it is not clear if they ever occur in Antarctic waters.

Resident killer whales have been recorded diving to a maximum depth of 264 m (in water less than 330 m deep), and regularly dive deeper than 150 m, but spend more than 70% of their time at depths less than 20 m. Mean dive durations are typically short, around 1-2 minutes, with a maximum dive duration of 17 minutes recorded. Bigg’s killer whales have a maximum recorded dive depth of 254 m, but a single Bigg’s spent more than two-thirds of its time at depths between 20 and 60 m, and a study of 11 Biggs’ showed that they spend more than 90% of their time shallower than 40 m, and more than 50% of their time shallower than 8 m. Maximum recorded dive duration is 11 minutes. It has been suggested that Biggs’ killer whales dive to depths where they can see prey swimming above them. In Antarctica, Gerlache killer whales have been recorded diving deeper than 500m.

Group sizes vary widely, from solitary individuals to groups of several hundred animals. Type A killer whale groups appear usually to be fewer than 20 animals. Pack ice killer whale groups are often less than 10 animals, while Gerlache killer whale groups often number 50 or more. Ross Sea killer whale groups are larger still, with some groups larger than 100 but these may represent several groups coming together for feeding or socializing. Subantarctic killer whales are known only from a single stranding event in 1955 and a small number of recent at-sea sightings. Reported group sizes average 18 individuals, ranging from 9-35.
Very little is known of the social organization of killer whales around Antarctica, but this can presumably be inferred to some degree from long term studies at other locations. Killer whales are very social and show strong, long-term associations between individuals. In the eastern North Pacific fish-eating resident killer whales show lifelong association between mothers and their offspring, meaning individuals never disperse from their natal social unit. The basic social unit – the ‘matriline’ – is a stable group of 2-9 (on average, 4) animals which comprises a female and as many as three generations of her and her daughter’s offspring. One to three matrilines that likely share a common maternal ancestor form a ‘pod’ – a less stable social unit in which the matrilines may be apart for weeks or months – and pods form clans, which are defined by the similarity of their vocal behaviour. Mammal-eating transient (or Bigg’s) killer whales are socially philopatric to a lesser degree, with dispersal occurring in both sexes. This difference in social organization likely arises from the constraints on group size for mammal-eating killer whales in general. Bigg’s matrilines typically contain only an adult female and one or two of her offspring and interactions among matrilines are dynamic, such that there is no unit equivalent to the resident pod. Long-term data from the Crozet Islands demonstrate long-lasting social bonds with pods (in this case, animals which spend more than 50% of their time together) of 1-10 animals. Preliminary findings from the Prince Edwards Islands indicate a social structure similar to that of eastern North Pacific Bigg’s killer whales.
Like other odontocetes, killer whales use sound for echolocation and communication. They produce three distinct types of vocalizations: echolocation clicks, whistles, and pulsed calls. Clicks are short pulses of sound, usually produced in a series, and are used in echolocation for orientation and prey detection. Whistles and pulsed calls are thought to play a role in communication. In the eastern North Pacific, resident killer whales whistles are heard primarily in social situations when whales are close together whereas pulsed calls are heard most often when whales are spread out and foraging, or when groups meet. The most common pulsed calls of resident killer whales are ‘discrete calls’ and pods have unique vocal repertoires or ‘dialects’ of 7-17 of these calls. A portion of this vocal repertoire may be shared with other pods and the degree of similarity in calls reflects relatedness of the pods. These dialects are stable over generations and likely culturally transmitted through vocal mimicry in offspring. Bigg’s killer whales vocalize less and produce more single (or ‘cryptic’) echolocation clicks to avoid being detected by their mammalian prey. Presumably they rely on passive listening as well as vision to detect their prey. Purported Ross Sea killer whales recorded near McMurdo Sound, Ross Sea, produced at least 7 discrete calls. While geographic variation was evident, their vocalizations had a similar structure to eastern North Pacific residents’.
Aerial behaviours such as breaching, spyhopping, lobtailing and flipper slapping are common, particularly while animals are socializing.

Killer whales may occur in all marine habitats. See Species distribution, below, for details pertaining to Southern Ocean types.

Killer whales are the oceans’ apex predators. Collectively, they prey on a wide variety of taxa including cephalopods, bony and cartilaginous fishes, reptiles, birds, and mammals. Members of all marine mammal families except the river dolphins and manatees have been recorded as prey and attacks have been observed on at least 35 species of marine mammals. Numerous fish species are included in their diet (at least 22 in the eastern North Pacific alone), notably salmon (Oncorhyncus spp.), herring (Clupea harengus), cod (Gadus spp.), tuna (Thunnus spp.) and various elasmobranchs. In total, over 140 species of marine vertebrates have been reported as killer whale prey. Despite this generally eclectic diet, prey specialization is one of the most striking features of killer whale ecology, and many ecotypes seem to feed on a narrow range of prey.
In the Southern Ocean, type A killer whales are proposed to specialize on Antarctic minke whales (Balaenoptera bonaerensis) but have on occasion been seen to prey on elephant seals (Mirounga leonina). Pack ice killer whales feed almost exclusively on seals (especially Weddell seals [Leptonychotes weddelli]) but have been observed taking Antarctic minke whales on occasion. Gerlache killer whales may feed mainly on fish but they also take penguins (gentoo penguins [Pygoscelis papua] and chinstrap penguins [Pygoscelis antarctica]). Ross Sea killer whales are putative fish specialists (particularly Antarctic toothfish [Dissostichus mawsonii]). The diet of Subantarctic killer whales is unknown, but they may feed on fish as they have been observed interacting with longline fisheries. Killer whales at the subantarctic Crozet Islands (which appear most similar to Antarctic type A killer whales) seem to be generalists, taking elephant seals, fur seals, penguins, large whales and fish. Individuals at the subantarctic Prince Edward Islands (some of which are similar to type A; others appear similar to pack ice killer whales) prey on elephant seals, subantarctic fur seals (Arctocephalus tropicalis) and penguins.
In some cases, remarkable and spectacular hunting strategies are employed. At Crozet, as well as northern Patagonia, Argentina, killer whales intentionally strand themselves to catch pinnipeds, a behaviour which appears to be taught to younger animals. Pack ice killer whales use a cooperative ‘wave-washing’ technique to hunt seals on ice floes. Killer whales lift their head vertically out of the water (‘spyhop’) to visually detect seals resting on ice floes, and upon finding one may spyhop repeatedly to identify the species; they overwhelmingly prefer Weddell seals. A group of whales will then arrange themselves in a line abreast and swim rapidly underwater towards the floe with their flukes beating quickly and synchronously. They produce a wave up to 1 m high which washes seals off smaller floes – which they attack – or breaks up larger floes, which can then be wave-washed. In several areas of the subantarctic, killer whales have become adept at depredating Patagonian toothfish (Dissostichus eleginoides) from longline fisheries.

In resident killer whales, calving occurs year-round with a peak between autumn and spring. In captive killer whales gestation ranged from 15-18 months, with a mean of 517 days. A single calf is usually born; twins are infrequent. Calves take solid food from a very young age (as early as a few weeks) but nurse for at least a year. Weaning age is not known but is probably 1-2 years and calves are probably not fully weaned until near 4 years. Calving intervals in resident killer whales were 2-12 years, with a mean around 5 years and neonatal mortality (before 6 months of age) was high – from 37- 50%. Data from whales caught in the southern African subregion and Antarctica suggest calving intervals of 3.5 – 5.2 years. The age at which resident females typically gave birth to their first viable calves (calves surviving longer than 6 months) was 12-16 years, with a mean around 15 years. These females had reproductive lifespans of approximately 21-27 years (mean of 25 years) during which time they gave birth to around 5 calves. Mean total longevity was 50 years, and maximum longevity was 80-90 years, indicating a long post-reproductive lifespan of up to 30 years or more, which is very rare among non-human animals. It has been shown that post-reproductive females increase the survival of their offspring, particularly older males, thereby increasing their own inclusive fitness. Male Biggs’ became sexually mature at 15 years, had an average lifespan of 30 years and maximum age of 50-60 years.

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