Special features of chum salmon Oncorhynchus keta (Salmonidae) stock formation in the Southwestern Sakhalin fish hatcheries as identified using the otolith marking method

The results of a study of the formation of chum salmon Oncorhynchus keta stocks at the Kalininsky, Sokol’nikovsky, and Yasnomorsky salmon hatcheries, located in the southwestern part of Sakhalin Island, using the method of otolith marking of juveniles are presented. According to long-term data, the commercial stocks of all hatcheries are formed by both hatchery production and natural spawning; they are significantly dominated by individuals of older age groups, and the numbers of fish of the respective generations at all hatcheries are closely correlated. The stock of the Kalininsky hatchery is mostly formed due to the work of the farm itself. The Sokol’nikovsky hatchery stock is greatly influenced by the work of neighboring farms: the number of brood fish with tags of Kalininsky and Yasnomorsky hatcheries among the fishes that approached this hatchery becomes clearly pronounced in years with low catches in the region. In stocks of the Yasnomorsky hatchery, brood fish with marks of neighboring farms were also revealed. However, the formation of the Yasnomorsky hatchery stock is influenced more, compared to the stocks of other farms, by natural reproduction and primarily by spawning in the Yasnomorka River, which is the most productive chum salmon riverin the southwestern part of Sakhalin.