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Catch of walleye pollock by Russia is the highest in the northern Okhotsk Sea where on average 0.94 million metric tons were caught annually in the period between 1962 and 2017, or around 24 % of the total yield of Russian fishery. The total stock and spawning stock of pollock grow there since 2002, though the catch per unit effort (CPUE) has significantly decreased in the beginning of 2018 despite expected high levels of both total and spawning stocks. The sea surface temperature, ice cover and storms frequency were examined as possible reasons of low fishing efficiency in 2018. For this purpose, the generalized linear models (GLM) and generalized additive models (GAM) of catch dynamics are compared. GAM with addition of temperature and storms factors has the lowest Schwarz’s Bayesian criterion and the highest explained deviance (61.6 %). Efficiency of fishing gears has nonlinear relationship with the towing time. CPUE has hypersensitivity to the stock biomass presented as the power dependence (γ = 0.94, r = 0.923). Standardized CPUE is recommended for using in the final GAM for the pollock stock assessment in the northern Okhotsk Sea, hypersensitivity of CPUE should be estimated and corrected if necessary.

A possible model approach to stock assessment of marine commercial invertebrates is discussed based on modeling of year-to-year dynamics for three functional groups (recruits, prerecruits, and commercial males). The model parameters are determined by joint solution of the tasks of optimal filtration and identification. As an example, this approach is used for assessment of the stock of king crab on the shelf of West Kamchatka. For this case, the data on actual catch are used obtained from reports of customs in Japan, Korea, USA, and China about the volume of crab products imported from Russia. The modeling confirms the conclusion from direct observations about rapid growth of the red king crab stock at West Kamchatka in recent years. Following to these results, the value of total allowable catch (TAC) can be substantially increased for this species. The officially recommended TAC of red king crab at West Kamchatka for 2016 is below of the 95 % confidence interval of the really possible catch. This value does not account the species stock recovery and hamper rational utilization of the valued natural resource.

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On example of walleye pollock at East Kamchatka, one of possible approaches is considered to assess the state of stocks for marine commercial species with usage of the data on age structure in catches. Algorithms for suboptimal filtering and interpolation (extended Kalman smoother and unscented Kalman smoother) are presented for a cohort model of an exploited stock, in presence of uncertainty about true value of the vector of the system parameters.