No abstract

Aggregate hatchery production of Pacific salmon in the Kamchatka region of the Russian Federation is very low (< 0.5% of total harvest, with five hatcheries releasing approximately 41 M juvenile salmon annually), but contributions in certain rivers can be substantial. Enhancement programs in these rivers may strongly influence fitness and production of wild salmon. In this paper we document significant divergence in demographic traits in hatchery salmon populations in the Bolshaya River and we estimate the proportion of hatchery chum salmon in the total run in the Paratunka River to demonstrate the magnitude of enhancement in this system. We observed a reduction in the expression of life history types in hatchery populations (ranging from 1 to 9 types) compared to wild populations (17 types) of sockeye salmon in the Bolshaya River. We found similar trends in Chinook salmon in the same river system. This reduced life history diversity may make these fish less resilient to changes in habitat and climate. We estimate hatchery chum salmon currently contribute 17-45% to the natural spawning population in the Paratunka River. As hatchery fish increase in numbers at natural spawning sites, this hatchery production may affect wild salmon production. It is important to investigate the risk of introgression between hatchery and wild salmon that can lead to reduction in salmon fitness in Kamchatka rivers, as well as the potential of ecological interactions that can have consequences on status of wild salmon and overall salmon production in this region.

Data on quantitative distribution of early and late spawners of sockeye salmon in the Lake Nachikinskoye basin were collected in 2019 using quadcopter. Features of sockeye spawning in certain sectors of the lake coast and at the spawning stations are analyzed. The spawning starts earlier on the eastern coast, and then on the western coast. The late sockeye spawning is considered in details at the spawning stations on littoral shelves, on steep coastal slopes, in key limnocrenes, in algae fields at the depths up to 5 m, and in the river tributaries. Environmental conditions of the stations are compared quantitatively by several parameters, as water flows and their gradients, water temperature, dissolved oxygen content, soils composition, impact of predators and waves. Each station has its advantages and disadvantages. The lake shallows dominate among the spawning grounds, but their diversity provides stability and even growth of local sockeye salmon stocks. Spatial distribution of the sockeye spawning grounds is described. The number of spawned fish is assessed using the trapezoid approximation (TAUC) as 55 . 103 ind. for early sockeye and 132 . 103 ind. for late sockeye that shows a considerable growth of the stocks of sockeye salmon in Lake Nachikinskoye since the middle of last century.

Residence time of late-race sockeye spawners on spawning grounds located in the littoral zone of Lake Nachikinskoye in southern Kamchatka is determined directly using 11 series of tagging and tracking of tags conducted in 2018 and 2020 (700 tagged individuals). The residence time is the key parameter for calculation of the spawners number on the data of repeated observations from the beginning to the end of spawning. Methodology of the experiment is described in details and all data of measurements are presented. Impact of certain variables on the target function is discussed. The residence time is estimated as 5 days.

State of the spawning part of the sockeye salmon population in Lake Nachikinskoye is characterized. Adults of the early race enter the lake from the sea in spring and early summer, mature at a depth and spawn from July to late August in three different loci — creeks, springs and lake, forming the corresponding ecotypes. The late race representatives enter the lake in July-August, mature, and spawn until December in the same loci. The races differ in age structure, size and fecundity. Males dominate in both races, with a growing proportion of small-sized individuals. According to the materials of aero surveys, the number of fish on the spawning grounds decreased gradually until 2016. Recent data are presented for the number of sockeye salmon belonged to early and late races on certain spawning grounds in the lake basin, based on results of quadrocopter surveys in 2018–2021. The number of the early race spawners was ~100–400 × 103 ind., late race ~300–500 × 103 ind.; the fluctuations were not synchronous between the races. These great spawning stocks require reliable protection and detailed annual monitoring to predict further changes.