ABSTRACT
Kamchatka steelhead Oncorhynchus mykiss are the last of their race where the natural diversity of population structure still exists and all stocks remain free of genetic interactions from fish-culture operations. In recent years, the number of Kamchatka steelhead populations, especially anadromous forms, has declined sharply. The present study is based on previous data (1971–72) and on results of joint Russian-American expeditions conducted during 1994 and 1995. In Asia, O. mykiss primarily occurs in small tundra rivers of the Kamchatka Peninsula and Bolshoy Shantar Island. Throughout its range, O. mykiss is represented by anadromous and resident forms. The typically anadromous form of steelhead is of the stream-maturing type, which enters the rivers with immature gonads in fall, stays there in winter, and spawns in early spring. The life strategy and structure of steelhead populations can change over time. In the Utkholok River, the correlation of the intrapopulation groups has changed in favor of coastal and river forms as a result of declines in the typically anadromous form. Understanding and protecting the natural diversity of population structure and life history forms are critical to sustaining the biological diversity inherent to O. mykiss.
