Assessment of the state of Pacific salmon hatchery stock and reproduction efficiency in the Bolshaya River (West Kamchatka)

State of Pacific salmon hatchery stock, reared in Malkinsky SH (warm watered) and Ozerki SH (cold watered) was evaluated as a result of carried work. On the data for 2001–2025 the long-term average juvenile releases were as next: about 0.7 mln sockeye salmon individuals and 0.9 mln Chinook salmon individuals from Malkinsky SH and about11.7 mln sockeye salmon and 2.5 mln chum salmon individuals from Ozerki SH. On the data for 2010–2024 the long-term average estimates of returns (runs) of hatchery spawners into the Bolshaya R. were as next: 52.40 mln sockeye salmon individuals, 0.98 mln chinook salmon individuals and 21.10 mln chum salmon individuals. The contribution of the fish into the total stock structure (wild and hatchery fish) by species was: 8.1% for sockeye salmon, 13.4% and 3.9% for chinook and chum salmon respectively.The run dynamics of hatchery Pacific salmon in the Bolshaya R. in 2010–2024 is quite stable. Weakly defined trends in the increase in the number of chinook and sockeye salmon runs are noted. As for chum salmon runs, a slight trend to decrease is noted.Comparative evaluation of the efficiency of Malkinsky and Ozerki hatcheries in case of sockeye salmon has demonstrated a high level of runs to the “warm watered” hatchery. On the data for 2007–2020 the average long-term coefficients of return (RC) for the species were 5.57% in Malkinsky and 0.14% in Ozerki SHs. For chinook and chum salmons the RCs were 0.11% and 0.88%, respectively.The contribution of the artificial reproduction into the Pacific salmon stock in the basin of the Bolshaya R. exceeded the 5% threshold recognized internationally as maximum acceptable for aquatic objects of natural reproduction of salmon stocks. That requires a categorical ban on the potential construction of new SHs in this basin. Moreover, the long-term values 0.1–0.9% obtained for cold watered Ozerki say in favor of unprofitability of Pacific salmon artificial cultivation for the hatcheries of such type within Kamchatka Territory.