Genetic identification of juvenile chum salmon of the Okhotsk Sea basin in mixed trawl catches

The objective of this study was to conduct regional genetic identification of juvenile chum salmon (Oncorhynchus keta) within mixed aggregations in the Okhotsk Sea based on materials from the autumn trawl survey of 2021, in order to estimate stock abundance and forecast returns of the 2020 year-class.

The research methods included analysis of polymorphism at eight microsatellite loci (Ssa20.19, One101, Oke3, Oki1b, Oki23, Ogo2G, Oke11, Ots102), as well as statistical analysis and genetic identification using a reference database of allele frequencies for chum salmon populations from the Okhotsk Sea basin and the software packages Cervus, GDA, ONCOR, and GenClass2.

The results of genetic identification made it possible to determine the proportions of juvenile chum salmon originating from the main spawning regions of the Okhotsk Sea basin, with a predominance of individuals from Sakhalin Island (31 %), followed by the Amur River basin (27 %), Iturup Island (22 %), and Western Kamchatka together with the northern mainland coast of the Okhotsk Sea (19 %). Based on the identification results, the expected number of returning adult chum salmon from the 2020 year-class of Western Kamchatka origin was estimated. These estimates correspond to the already observed returns of age group 3+ and the preliminary evaluations for group 4+. This indicates a positive consistency between genetically derived estimates and the actual data at the current stage of research, while final conclusions regarding the reliability of the approach will require accumulation of multi-year observations.

The practical significance of the study lies in improving the accuracy of chum salmon stock monitoring and refining the predictive assessments of spawning returns, thereby contributing to the development of more scientifically grounded recommendations for the sustainable management of salmon resources in the Far Eastern fisheries basin.

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