Orca types and populations

Orcas or killer whales have a cosmopolitan distribution and several distinct populations or types have been documented or suggested. Three to five types of orcas may be distinct enough to be considered different races, subspecies, or possibly even species (see species problem). 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." However, large variation in the ecological distinctiveness of different orca groups complicate simple differentiation into types. Mammal-eating orcas in different regions were long thought likely to be closely related, but genetic testing has refuted this hypothesis.
Research off the west coast of Canada and the United States in the 1970s and 1980s identified the following three types:
Separate fish-eating and mammal-eating orca communities also exist off the coast of the Russian Far East and Hokkaido, Japan. Russian orcas are commonly seen around the Kamchatka Peninsula and Commander Islands. Over 2,000 individual resident-like orcas and 130 transient-like orcas have been identified off Russia. At least 195 individual orcas have been cataloged in the eastern tropical Pacific, ranging from Baja California and the Gulf of California in the north to the northwest coast of South America in the south and west towards Hawaii. Orcas appear to regularly occur off the Galápagos Islands. Orcas sighted in Hawaiian waters may belong to a greater population in the central Pacific.
At least 15,000 whales are estimated to inhabit the North Atlantic. In the Northeast Atlantic, two orca ecotypes have been proposed. Type 1 orcas consist of seven haplotypes and include herring-eating orcas of Norway and Iceland and mackerel-eating orcas of the North Sea, as well as seal-eating orcas off Norway. Type 2 orcas consist of two haplotypes, and mainly feed on baleen whales. These two types have now been dropped from the classification, because of a lack of samples for type 2 (5 individuals) and how little it was representative of a potential ecotype.
In the Mediterranean Sea, orcas are considered "visitors", likely from the North Atlantic, and sightings become less frequent further east. However, a small year-round population exists in the Strait of Gibraltar, which numbered around 39 in 2011. From 2020, this population started ramming vessels and damaging their rudders. Distinct populations may also exist off the west coast of tropical Africa, which have generalized diets.
The northwest Atlantic population is found year-round around Labrador and Newfoundland, while some individuals seasonally travel to the waters of the eastern Canadian Arctic when the ice has melted. Sightings of these whales have been documented as far south as Cape Cod and Long Island. This population is possibly continuous with orcas sighted off Greenland. Orcas are sighted year-round in the Caribbean Sea, and an estimated 267 (as of 2020) are documented in the northern Gulf of Mexico.
Recent studies using dietary tracers such as fatty acids and organic contaminants have shown how varied the diet of North Atlantic orcas is. For example, orcas in the Eastern North Atlantic (Norway, Faroe Islands, Iceland) mainly feed on fish, specifically herring. Meanwhile, those in the Central North Atlantic (Greenland) prefer to consume seals such as ringed, harp, hooded, and bearded seals. Finally, orcas in the Western North Atlantic (Eastern Canadian Arctic and Eastern Canada) tend to prey on other whale species, such as belugas and narwhals in the Arctic and baleen whales and porpoises in Eastern Canada.
Over 50 individual whales have been cataloged in the northern Indian Ocean, including two individuals that were sighted in the Persian Gulf in 2008 and off Sri Lanka in 2015.
A small population of orcas seasonally visits the northern point of the Valdes Peninsula on the east coast of Argentina and hunt for sea lions and elephant seals on the shore, temporary stranding themselves. Similar behaviors occur among orcas off the Crozet Islands, which breach to grab elephant seals. These orcas also prey on Patagonian toothfish. 65 individuals have been documented in this area. Off South Africa, a distinctive "flat-tooth" morphotype exists and preys on sharks. A pair of male orcas, Port and Starboard, have become well known for hunting great whites and other sharks off the South African coast.
Orcas occur throughout the waters of Australia, New Zealand and Papua New Guinea. They are sighted year round in New Zealand waters, while off Australia, they are seasonally concentrated off the northwest, in the inshore waters of Ningaloo Reef, and the southwest, at the Bremer region. Genetic evidence shows that the orcas of New Zealand and northwest and southwest Australia form three distinct populations. New Zealand orcas mainly prey on sharks and rays.
Around 25,000 orcas are estimated around the Antarctic, and four types have been documented. 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.
Types B and C live close to the ice, 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 types B and C 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. A 2019 study of Type D orcas also found them to be distinct from other populations and possibly even a unique species.