This issue of the magazine is thematic. It is dedicated to the 80th anniversary of the KamchatNIRO scientific observation station on the Kurile Lake – the cradle of sockeye salmon (Oncorhynchus nerka)
in the Ozernaya River basin, the biggest stock of this species of Pacific salmon in Asia.

Description of summer hydrometeorological conditions is provided for the period from 1976 to 2020. Statistical evaluations of the time series of the entire hydrometeorological dataset collected at the KamchatNIRO observation station ashore of the Ozernaya River emerge from Kurile Lake have been obtained. Analysis of linear trends has been accomplished. Revealed rise of the air temperature at the Ozernaya meteostation and Kurile Lake and of the water temperature in the Ozernaya River is reckoned higher compared global trends. The correlations found between temperature characteristics were significant. The correlation coefficients between the air temperature at the Ozernaya meteostation and Kurile Lake either water temperature in the Ozernaya River demonstrate increase averaged for season and from 0.3 in June to 0.6–0.8 in August. The rest of the parameters correlated weaker, and there were few significant ones. Stable significant correlations were revealed between temperature characteristics and global temperature indices. Also linear correlations between the WP index, characterizing low-frequency variability in the atmosphere in the West Pacific, and a number of parameters averaged for the season or in different months were meaningful. Spectral analysis with confidence interval of 95% revealed only the spectral harmonics of interannual fluctuations in the amount of precipitation for the season with a period of 2.2 years as significant.

Results of a study of the taxonomic, size and vertical structure of littoral plankton in the lake, river and spring spawning grounds of the Kurile Lake are presented. Seasonal and local variability of plankton in these biotopes, where the main components were pelagic crustaceans (Cyclops scutifer, Daphnia longiremis) and chironomid larvae, mostly small-sized ones, are discussed.

Characteristics of qualitative and quantitative composition of benthos organisms on littoral and spring spawning grounds of Kurile Lake was given for the first time in 1974. Grounds of the littoral and spring spawning grounds typically consist of intermiting plots of pebble or gravel (clean or covered by biocrust) with permanent sand component, sometime silty. The silt component in the spring spawning grounds in the rivers Srednaya and Kirushutk is more impressive comparing to the lake spawning grounds. Chironomids of the group Crico­ topus aff аlgarum dominated in all sites. In the mid of July the highest biomass of the benthos among the littoral spawning grounds was near the head of the Ozernaya River, at Severnoye Blizhneye and Severnoye Dalneye spawning grounds, the lowest biomass was in the Gavryushka Bay and near the Etamynk River mouth. Spring spawning grounds were extensively different: maximum biomass of the benthos, which almost totally consisted of chironomids, was typically recorded in the Srednaya River, minimum biomass — in the Kirushutk River.

Direct observations were used to study feeding by Daphnia longiremis Sars in the Kurile Lake (South Kamchatka) in terms of structural transformation of phytoplankton in 2008. Spectrum of the daphnia’s food reflects transformations in phytoplankton species structure. Daphnia’s consumption intensity of phytoplankton, where 99.8% were diatom cells, depends on the phytoplankton biomass. It is suggested, that daphnias meet deficient in food when the values of the phytoplankton (plankton diatoms) biomass are less than 48 mgС/m3 and no compensation of plankton bacteria or detritus.

A study was made of the nutrition of different-sized sockeye salmon underyearlings during the littoral feeding period in the summer-autumn period of 1972 on lake and river habitats. Diet of 2and 3-year-old sockeye salmon individuals sampled in pelagic zone was analyzed also. It was found, that permanent and dominating component in the diet of the age groups 0+, 1+ and 2+ of juvenile sockeye salmon in the littoral and pelagic zones of Kurile Lake was plankton crustacean Cyclops scutifer: up to 1700 individuals per one stomach, making 33.3–99.6% of the stomach content. Juvenile sockeye salmon were feeding on the cyclops of various ontogenetic stages, the bigger were juvenule sockeye salmon individuals, the higher was the part of large copepodids of late stages, mature individuals. The other components of the diet included larval chironomids, which role was maximum in feeding of underyearlings with the body length 26–30 mm, pupal chironomids and imago aerial insects. Index of fullness of the underyearling stomach in the samples from the lake littoral and composition of the forage spectra indicated that condition of feeding were different in different habitats.

Original thechnique of counting Pacific salmon on fish counting facility located at the head of the Ozernaya River, at KamchatNIRO survey station, is presented for the first time.

Results of investigations of spawning run and quantitative assessment of Pacific salmon (pink salmon, chum salmon, coho salmon and chinook salmon) obtained during counting the sockeye salmon at fish enumeration facility in the headwaters of the Ozernaya River. It is revealed that abundance of various Pacific salmon species except sockeye salmon reaches significant values in some years in Kurile Lake. The presented data supplement knowledge about biology and reproductive ecology of pink salmon, chum salmon, coho salmon and chinook salmon.

Long-term (2004–2018) virological studies have shown that the Kurile Lake is a natural focus of infectious hematopoietic necrosis virus (IHNV). A hypothesis about the survival of the virus as a species is discussed. The results of the phylogenetic analysis of the midG region showed that typical IHNV genetic sequences found in sockeye salmon from Kurile Lake are unique and have single mutations. This confirms the assumption that the lake is a closed system, and fish from other reservoirs were not brought into it.