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." Although 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.
Northern waters
North Pacific
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. Resident orcas can be divided into at least three distinct communities; northern, southern and southern Alaskan. Southern Alaskan resident orcas are distributed from southeastern Alaska to the Kodiak Archipelago and number over 700 individuals. These whales consist of two interbreeding clans distinguished by acoustic calls and whose ranges overlap. The northern resident community lives in coastal and inland waters from southeastern Alaska to Vancouver Island. It consists of three clans and 16 pods and number over 300 orcas total. The southern resident community generally inhabits the inland waters of southern British Columbia and Washington, but can be found in the outer waters off Vancouver Island, Washington, Oregon and California. They consist of one clan and three pods, and number less than 80 individuals and are listed as endangered.