Orca

The killer whale, also known as the orca, is the ocean's top predator and the largest member of the Delphinidae family, the dolphins. It is found in every ocean in the world and is the most widely distributed of all cetaceans. Technically it is the largest dolphin species, though it is called a whale because of its large size.

The killer whale is still treated as a single species, yet there is extensive and growing evidence that it is in fact a complex of multiple forms with morphological, genetic, ecological and behavioural differences that merit subspecies, if not also species, designations. At least eight recognised forms differ in external colouring, appearance, feeding habits and ecology. Genetic studies show that orca populations have diverged primarily as a result of feeding specialization, with distinct mammal-eating and fish-eating populations. Numerous ecotypes have been identified on the basis of morphology and diet, including specialists that eat marine mammals, or fish and even sharks.

A team of NOAA Fisheries and university scientists published research in Royal Society Open Science showing that West Coast resident and Bigg's killer whales are different species. A review and new analyses indicate that species-level status is justified for eastern North Pacific Bigg's killer whales and resident killer whales. Resident and Bigg's killer whales are the first separately identified species of killer whales, breaking from the longstanding view that all killer whales belong to one worldwide species. Because the two binomials are described in the same publication with no prior names from the North Pacific, the authors proposed Orcinus ater and Orcinus rectipinnus for the resident and Bigg's species respectively.

The name Orcinus ater dates from Cope in Scammon during 1869, and in Latin ater means black or dark, which probably refers to the largely black colour of this species. Cope edited and then published Scammon's manuscript in 1869 in the Proceedings of the Academy of Natural Sciences of Philadelphia.

The killer whale, or orca, is a large dolphin whose maximum male length exceeds 10 metres, while females measure about 8.5 metres. One survey of Antarctic animals gives males a length of about 9.75 m and females 8.5 m, and notes that mature males are obvious because of their very tall dorsal fin. A separate account places the species at up to 9 metres in length, with the dorsal fins of males reaching higher than a metre.

In older males the dorsal fin is very tall, up to 1.8 metres, and straight, whereas females and young males carry a distinctly sickle-shaped fin about half that size. The skull holds the largest brain of all the dolphins. Newborn calves are from 2 to 2.4 metres long and weigh about 136 kilograms at birth.

Killer whales occupy every ocean from the Arctic to the Antarctic. In the North Pacific, three ecotypes are recognised — Resident, Transient and Offshore — which differ in appearance, diet, habitat, genetics and behaviour. Transient whales take a more varied diet that includes squid and marine mammals such as seals, sea lions, porpoises, dolphins and other whales. Offshore whales range more widely than any other community and often occur more than 9 miles from shore.

Antarctic waters hold five distinct forms — Types A, B1, B2, C and D — that differ markedly in phenotype, genetics and culture. Type A, which has a medium eyepatch parallel to the body axis and no dorsal cape, is circumpolar, occurs mainly offshore in ice-free water and preys chiefly on Antarctic minke whales. Type C, with its small forward-slanted eyepatch and dorsal cape, lives inshore, mainly in the pack ice off East Antarctica, and has been recorded feeding only on Antarctic toothfish. Type D, the subantarctic killer whale, is the rarest and least known of the forms and remains largely unstudied. Telemetry indicates that the ecotypes share a common long-distance migration, probably tied to physiological needs such as skin maintenance rather than to foraging alone.

Regional behaviour varies with local prey and terrain. Norwegian whales feed on herring and other fish, and large numbers gather each autumn in the Norwegian Tysk Fjord to prey on spawning herring. Patagonian whales beach themselves to take sea lion pups in shallow water. Orcas are common in Antarctic waters and can live deep in the pack ice even in winter, with rare sightings recorded deep inside the pack ice in midwinter.

The killer whale has the most varied diet of all cetaceans, taking fish, squid, seabirds and marine mammals including other whales; the wider prey list covers most marine mammal species, seabirds, sea turtles, many fish such as sharks and rays, and cephalopods. It is the only known predator of great white sharks, and attacks or kills have been documented on more than 35 species, including blue whales. Average intake is about 45 kilograms of food a day, with capacity for much more.

Hunting methods are coordinated team strategies likened to a pack of wolves. Killer whale foraging tactics include intentional beaching to capture pinnipeds on shore, creating waves to wash seals off ice floes, and cooperative techniques to herd fish and attack large prey such as tuna and large whales. Hunting techniques are passed down through generations, so diets depend on the region and the pod's approach to hunting. Resident pods tend to prefer fish while transient pods target marine mammals. No records exist of deliberate fatal attacks on humans.

Killer whale society is built on matrilineal relationships, and when food is hard to find the oldest female leads the group, as she is likely to be the most experienced hunter. Highly organised clans maintain their own vocal communication dialects: pods have unique calls for their family group as well as calls they share with other groups, and pods that share at least one call type are called an acoustic clan. The social divisions between groups of killer whales with different hunting strategies and songs are so pronounced that scientists believe it is unlikely the groups socialise or interbreed.

The bond between mother and offspring carries consequences that extend well beyond the rearing years. Studies of killer whale lifespans found that when their mother dies, adult males have something like an eightfold likelihood of dying in the next couple of years.

Gestation in the orca lasts about 17 months.

Among fish-eating killer whales, low availability of Chinook salmon appears to be an important stressor as well as a significant cause of late pregnancy failure, including unobserved perinatal loss. Southern Resident killer whales had a 69 percent pregnancy failure rate during the study, and an unprecedented half of those occurred at later stages of reproduction. The consistency of pregnancy-failure patterns on multiple endocrine and temporal measures across years strengthens the assertion that pregnancy failure is a major constraint on killer whale population growth triggered by insufficient prey.

Killer whales are widely distributed, but the precision of any global count is limited by uneven survey coverage. A minimum worldwide abundance estimate of about 50,000 killer whales of all types was derived for sampled areas, and the true total is likely higher because many high-latitude and South Pacific areas lack estimates ^{3Orcinus orca, Killer Whale — The IUCN Red List of Threatened Species (Reeves, Pitman & Ford 2017) · International Union for Conservation of Nature (IUCN) ↗}. A comparable figure places around 50,000 killer whales globally, with approximately 2,500 in the eastern North Pacific Ocean, home to the most well-studied populations ^{17Killer Whale: Populations · NOAA Fisheries ↗}. The global IUCN Red List status for the species is Data Deficient.

Killer whales were once the direct object of human predation on a commercial scale. They were actively hunted in Norway, Japan, the Soviet Union and the Antarctic until the 1980s, after which the practice contracted sharply. Today they are taken only in small numbers, either for food or as a population control measure in coastal fisheries in Japan, Greenland, Indonesia and the Caribbean islands.

Capture for display has not ended everywhere: live capture of killer whales for aquarium display and marine parks still occurs outside the United States. Populations also face food limitation, chemical contaminants, and disturbance from vessel traffic and sound.

One population has received formal legal recognition of its peril. The Southern Resident killer whale was listed as endangered under the Endangered Species Act on 18 November 2005, and that listing was updated on 14 April 2014 following a status review.

In the inland waters of Washington, two killer whale ecotypes occur: the Endangered Species Act-listed Southern Resident killer whale, a fish-eating population of 73 individuals in 2024, and the marine-mammal-eating Bigg's killer whales that prey on pinnipeds. Southern Resident killer whales spend several months of the summer and fall each year in Washington State's Puget Sound.

Since 1976 the Center for Whale Research in Washington State has run a long-term killer whale survey project whose demographic data support research on the species.

• 1758
  Linnaeus describes Delphinus orca
  The species is first described under the name Delphinus orca.
• 1869
  Cope in Scammon
  Origin of the name Orcinus ater.
• 1935–1979
  Soviet commercial whaling
  Soviet whalers take an average of 26 killer whales annually, primarily in the Antarctic. ^{3Orcinus orca, Killer Whale — The IUCN Red List of Threatened Species (Reeves, Pitman & Ford 2017) · International Union for Conservation of Nature (IUCN) ↗}
• 1962–1977
  Live captures
  At least 65 killer whales are live-captured in British Columbia and Puget Sound.
• 1974
  Southern Resident population
  Population stands at 71.
• 1976
  Center for Whale Research
  Survey project begins.
• 1979/80
  Soviet Antarctic season
  916 animals taken. ^{3Orcinus orca, Killer Whale — The IUCN Red List of Threatened Species (Reeves, Pitman & Ford 2017) · International Union for Conservation of Nature (IUCN) ↗}
• 1989
  Exxon Valdez oil spill
  The AT1 stock of transient killer whales in the eastern North Pacific falls from 22 to 6 whales after the spill. ^{17Killer Whale: Populations · NOAA Fisheries ↗}
• 1996
  Southern Resident peak
  Population reaches 97.
• 2001
  Southern Resident decline
  Population declines to 79.
• 2004
  AT1 designated depleted
  NOAA Fisheries designates the AT1 stock as depleted under the MMPA. ^{17Killer Whale: Populations · NOAA Fisheries ↗}
• 18 November 2005
  Southern Resident listed as endangered
  The Southern Resident killer whale is listed as endangered under the Endangered Species Act. ^{19Southern Resident Killer Whale (Orcinus orca) · NOAA Fisheries ↗}
• 2006
  Critical habitat and Gibraltar assessment
  Critical habitat is designated, and the Gibraltar subpopulation is provisionally proposed as Critically Endangered.
• 14 April 2014
  Listing updated
  The Southern Resident listing is updated following a status review. ^{19Southern Resident Killer Whale (Orcinus orca) · NOAA Fisheries ↗}
• 2019
  Gibraltar assessment
  The Gibraltar subpopulation is assessed as Critically Endangered.
• 2021
  Critical habitat revised
  Critical habitat is revised.
• 2024
  Southern Resident population
  Population stands at 73.