The Biology and Abundance of Sockeye Salmon Spawners in the Nachikinskoye Lake Basin (Southwestern Kamchatka)

State of the spawning part of the sockeye salmon population in the Nachikinskoye Lake were analyzed. Adults of the early run enter the lake from the sea in spring and early summer, mature in deep areas and spawn from July to the late August in three different types of localities: creeks, springs and lake, respectively forming three ecotypes. Late running fish enter the lake in July-August, mature, and spawn until December in the same localities. Fish from these two runs differ in their age structure, size and fecundity. Males dominate in numbers in both runs, with an increasing proportion of small individuals. Data from aerial surveys suggested that the number of fish on the spawning grounds decreased gradually until 2016. Drone surveys conducted in 2018-2021 provided data on sockeye salmon numbers from the early and late runs on different spawning grounds. The number of spawners from the early run ranged from 100 000-400 000 individuals, and from the late run from 300 000-500 000 individuals. Fluctuations in fish abundance were not synchronous in these two runs. The revealed abundant sockeye spawning stocks require strong protection and detailed annual monitoring to predict further changes in abundance.