Dynamics of the abundance and conditions of reproduction of mass species of pacific salmons (Oncorhynchus) on the northwestern coast of Sakhalin

The efficiency of reproduction of Pacific salmons of the genus Oncorhynchus in the rivers of the northwestern coast of Sakhalin Island is characterized on the basis of long-term data (1989−2014). Differences between the rivers in the northern and southern parts of the region under study have been revealed with respect to the channel type, faunistic composition of the aquatic biota, and prevailing species of salmons. A high spawning efficiency of pink salmon O. gorbuscha , high densities of filling of spawning grounds, and a relatively poor composition of the freshwater ichthyofauna have been recorded in the rivers of the northern part with the mountain–piedmont type of channel. Varied fish population and the high spawning efficiency of chum salmon O. keta have been recorded in the rivers of the southern part with the mainly lowland channel. The salmon spawning area in the rivers of the northern and southern parts has been estimated. The data on the dynamics of the abundance of salmons on the northwestern coast of Sakhalin are given. The total value of the passage of spawners to the rivers of northwestern Sakhalin that is required for effective reproduction has been estimated, ranging from 0.672 to 1.639 million specimens for pink salmon and approximately 0.43 million specimens for chum salmon.