ИСТИНА

The killer whale Orcinus orca has a world-wide distribution, but specific forms or ecotypes occur in particular regions. In the eastern North Pacific, three distinct reproductively isolated ecotypes have been described: fish-eating “residents”, mammal-eating “transients” and offshore killer whales that likely specialize on hunting sharks. Offshore killer whales typically occur far from the shore, while residents and transients share the same habitat in the coastal waters. In the western North Pacific, fish-eating and mammal-eating ecotypes have been described, resembling and related to the eastern North Pacific residents and transients, correspondingly. Here we report the differences in geographical distribution of fish-eating and mammal-eating killer whales revealed through surveys and opportunistic observations in different areas of the western North Pacific from the Okhotsk Sea to Chukotka in 2000-2017. Fish-eating killer whales prevailed in areas where relatively deep waters occurred close to the shore: eastern Kamchatka, Kuril and Commander Islands. On the contrary, in the areas with extensive coastal shallows (western and northern Okhotsk Sea, western Kamchatka, eastern Chukotka) only mammal-eating killer whales were observed. In Anadyr Gulf (central Chukotka) both ecotypes were registered, but encounters with mammal-eating killer whales were more common. Large-scale differences in ecotype distribution have not been described previously for the well-studied killer whale populations in the eastern North Pacific. There is some local habitat segregation: transient killer whales use small shallow bays more often than residents, but no major region of the eastern North Pacific has been reported to be exclusively visited by the whales of only one ecotype. We suggest several hypotheses to explain these differences, including ice distribution and cultural traditions among the local killer whale pods.