Longterm data on the liver weight, hepatosomatic (HSI) and gonadosomatic (GSI) indices of walleye pollock, Pacific cod and saffron cod are analyzed on Eastern Kamchatka in seasonal aspect and in the course of gonad maturation. Individual values of the indices extensively vary and depend on the fish body length, season and stage of gonad maturity. The dynamics of the HSI is agree to the dynamics of the GSI during the year and depending on gonad maturity. The maximum values of the HSI are typical for walleye pollock and Pacific cod individuals with the gonads of the III stage of maturity. The maximum values of the index in saffron cod are found in mature individuals with immature gonads. The minimum values are demonstrated by the fish with the gonads at the stage of final spawning or of post-spawning recovery. During the annual reproduction cycle males and females of walleye pollock and cod realize different scenarios of spending and accumulating liver fat. Whereas the maximum HSI is observed in the fish with the gonads at the III maturity stage, the minimum values in males are typical for individuals with smelting gonads, and in females – on finishing the spawn. That can be connected to possible feeding for the individual. Liver weight and liver index can increase in males just shortly after finishing spawning, in females that is found only at the stage of post-spawning recovery.

Data of trawl surveys for the period 2010–2017 revealed distribution of fry saffron cod in vicinity of river outlets, while juvenile walleye pollock was dictributed either near the shore or over the deepwater area in the southern part of shelf. In 2017 aggregations of saffron cod individuals with the body length 29.4–70.5 mm (averaged 52.9 mm) were observed in the area between 52° and 53°N at the depth range 14–195 m. The aggregation densities were maximum at the plots of the highest salinity, temperature and turbidity of the water and higher chlorophyll-a concentration. Principal catches of juvenile walleye pollock were in the area between 53° and 54°N at the depth from 20 to 195 m (averaged 68.2 mm). The aggregation densities of juvenile walleye pollock were maximal at the plots of higher salinity and oxygen concentrations. The concentration of chlorophyll-a was mediate at these plots, comparing to values in the area observed. The body length of the fry varied from 44.5 to 74.6 mm (57.8 mm averaged). Besides juvenile saffron cod and walleye pollock, adult and juvenile individuals of 11 bottom and demersal-pelagic species were found in the catches of the midwater trawl.

Analysis of the data of fish biology spring-summer researches in the Kichiga river basin in the period 2017–2019 for the first time brought results as next: characterized dynamics of chum salmon juvenile downstrean migration, including daily dynamics, revealed qualitative characteristics of the underyearlings, described diet of the juvenile migrants, demonstrated effects of the spring-summer hydrological regime on the intensity of the underyearling feeding. Also noted, that the conditions for the downstream migration of chum salmon in 2018 were maximum favouravle, and most likely that could enhance later juvenile survival.

The article presents results of examining possible competition between mass species of flounders for food resources in the eastern part of the Sea of Okhotsk. Comparative analysis of flounder feeding is provided in view of nonrandom forming food spectra as an effect of certain factor, which is interspecific competition in particular. Analysis of population growth rate dynamics was to find out mutual effects of the populations of different species on each other. General methods of the research included “neutral models” and Lotka – Volterra equations. Results indicate, that structure of flounder feeding had stabilized early under the influence of factors, including the interspecific competition. In most cases, the interspecific competition estimated per an individual is higher than intraspecific competition. Simulation has demonstrated, that flounder populations of the eastern part of the Sea of Okhotsk striving in their dynamics to the state of sustainable balance. Revealed competition between the flounder species for the resources is of assymmetric character.

Forecasting of pink salmon runs in Kamchatka uses modern powerful method of machine learning Random Forest (random forest of decision trees). Monthly data of climate indices are used as predictors. Forecasting applies iterative way of selection of the most important factors. Decision about the best model is based on the least error on test data. The algorithm of the method is written in R language.