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Orcas (Orcinus orca)

Also known as killer whales, these intelligent apex predators are the biggest of the dolphin family

An Orca or Killer Whale (orcinus orca)

Tom Brakefield/Alamy

Orcas, or killer whales, are aquatic mammals known as cetaceans and the largest member of the oceanic dolphin family. Males, which are bigger than females, can grow up to 8 metres long with a dorsal fin as tall as 1.8 metres.

Orcas are apex predators, meaning they are at the top of the food chain, and have been known to include fish, seals, rare beaked whales, sharks, birds and even other dolphins in their diet, with no species preying on them. Nevertheless – and despite their common name – they are not a threat to humans and a fatal attack has never been recorded in the wild.

Even for a cetacean, orcas are highly intelligent. Their behaviour is flexible enough to allow them to live in a range of marine environments in every ocean on Earth. Populations tend to carve out their own specialised niche in a single area, with a particular diet and sophisticated hunting habits. Some use bursts of bubbles to herd fish into bait balls, others deliberately strand themselves on beaches to capture the resident seals, and one pod has been seen working together to ambush dolphins.

Killer whales also have idiosyncratic vocalisations and communicate in distinct ‘dialects’, with one captive orca, Wikie, being trained to mimic human speech. In fact, their cultures are so distinct, that different populations tend not to interbreed, making them the only known non-human species in which culture shapes evolution.

Male orcas live on average between 29 and 60 years. Female orcas have a much longer lifespan, ranging on average between 50 and 80 years. It is believed their longevity stems from the fact that they are one of the few animals known to experience the menopause, extending their life well beyond childbearing age. This would seem to support the “grandmother hypothesis” in killer whales, which suggests that older females can pass on wisdom and experience without the costs of having more children.

Partly because of their wide distribution, it is unclear how many orcas exist worldwide and whether they are endangered. The International Union for Conservation of Nature (IUCN) has categorised orcas as a Data Deficient species, meaning there is not enough information to make a proper assessment of their conservation status. The number of orcas in the wild is thought to be around 50,000. Since August 2019 there are 60 orcas in captivity, of which nearly a third are in the United States.

Only one population is listed under the Endanger Species Act – the Southern Resident orca, which lives in the Salish Sea off the Pacific Northwest coast.  It consists of three inter-related pods, numbering 74 individuals in 2020. One of these, which the local Native American people call Sk’aliCh’elh-tenaut, has been in captivity for the past half century. The latest attempt to get her released could tap into a US law governing the return of objects of cultural importance to Native American peoples. If so, it would be the first time this law has been applied to a living being.