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绪论 虎鲸类型和种群（第3页）

North Pacific

Research off the west coast of Canada and the United States in the 1970s and 1980s identified the following three types:

Resident (fish-eating) orcas: The curved dorsal fins are typical of resident females.

Resident: These are the most monly 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 plex 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 munities; 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 munity 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 munity 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.

Transient or Bigg's: The diets of these orcas consist almost exclusively of marine mammals. They live in the same areas as residents， but the two avoid each other. Transients generally travel in small groups， usually of two to six animals， and have less persistent family bonds than residents. Transients vocalize in less variable and less plex dialects. Female transients are characterized by more triangular and pointed dorsal fins than those of residents. The grey or white area around the dorsal fin， known as the “saddle patch“， often contains some black colouring in residents. However， the saddle patches of transients are solid and uniformly grey. Transients roam widely along the coast; some individuals have been sighted in both southern Alaska and California. Transients are also referred to as Bigg's orca in honour of cetologist Michael Bigg. The term has bee increasingly mon and may eventually replace the transient label. The transient ecotype is estimated to have diverged 700，000 years ago. There are at least three different “stocks“ of transients off North America， the AT1 stock which occurs from Prince William Sound to Kenai Fjords， the Gulf of Alaska/Aleutian Islands/Bering Sea (GOA/AI/BS) stock and the west coast stock which ranges from southeast Alaska to California. AT1 is considered a depleted stock; it was affected by the Exxon Valdez oil spill and declined from 22 individuals to eight between 1989 and 2004. The GOA/AI/BS stock may number around 500 whales while the west coast transients number over 320 orcas with over 200 along southeast Alaska， British Columbia and Washington and over 100 orcas off California. California transients do not appear to intermingle much with those further north and west coast transients may be divided into sub-munities.

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Offshore: A third population of orcas in the northeast Pacific was discovered in 1988， when a humpback whale researcher observed them in open water. As their name suggests， they travel far from shore and feed primarily on schooling fish. However， because they have large， scarred and nicked dorsal fins resembling those of mammal-hunting transients， it may be that they also eat mammals and sharks. They have mostly been encountered off the west coast of Vancouver Island and near Haida Gwaii. Offshores typically congregate in groups of 20–75， with occasional sightings of larger groups of up to 200. Little is known about their habits， but they are genetically distinct from residents and transients. Offshores appear to be smaller than the others， and females are characterized by dorsal fin tips that are continuously rounded.

Separate fish-eating and mammal-eating orca munities also exist off the coast of the Russian Far East and Hokkaido， Japan. Russian orcas are monly 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.

North Atlantic and adjacent

Orca tail-slapping in Vestfjorden， Norway

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.

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In the Mediterranean Sea， orcas are considered “visitors“， likely from the North Atlantic， and sightings bee less frequent further east. However， a small year-round population exists in the Strait of Gibraltar， which numbered around 39 in 2011. 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) is documented in the northern Gulf of Mexico.

North Indian Ocean

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.

Southern waters