绪论 虎鲸类型和种群(第6/10 页)

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.

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 mander Islands. over 2，000 individual resident-like orcas and 130 tra