Resident Coho Salmon Oncorhynchus kisutch in the Asian Part of Range. Revisiting the Freshwater Component in the Structure of the Species

New data on the resident coho salmon Oncorhynchus kisutch from the water bodies of Kamchatka and the Bering Island (the Commander Islands) are presented: a typical resident life form is described in Kuril'skoye and Bol'shoye Lisinskoye Lakes; biological patterns of dwarf (neotenic) males of coho salmon from the basin of the Kol' River (Western Kamchatka) are presented. Composition and structure of freshwater groups of coho salmon were analyzed on the basis of our original materials and published data. New discoveries of resident coho salmon indicate its wider distribution in the Asian part of the range wider than it was previously thought. The freshwater component in coho salmon populations is heterogeneous and represented by three variants: 1) isolated lacustrine populations (typical resident form), 2) lacustrine-riverine individuals (typical resident form) of both sexes or males only, forming integrated reproductive complex with anadromous fish, 3) dwarf (neotenic) males which inhabit rivers without lakes in the basin. A hypothesis is considered that origin and distribution of resident forms of coho salmon in the Asian part of the range may be a consequence of large-scale climate changes in the North Pacific, which are occurring at the present time. The presence of polymorphic freshwater groups in coho salmon can be considered as a manifestation of a wide norm of reaction within the species, which provides complication of the structure of distinct populations, the appearance of additional elements in their composition and, consequently, an increase in their stability and adaptability to a dynamic environment.