Results of identification of autumn chum salmon Oncorhynchus keta (salmoniformes) of hatch-breeder origin in the Amur River basin based on the analysis of the microchemical composition of otoliths based on the materials of 2020

The paper presents the results of using microchemical analysis of otoliths to identify the return of autumn chum salmon, the juveniles of which are released from salmon hatcheries in the Amur basin. It was previously found that juvenile autumn chum salmon of hatchery origin were characterized by higher values of the 88 Sr/ 43 Ca ratio in the marginal zone of otoliths compared to juveniles of natural origin, which may be due to the high strontium content in the feed used to grow juveniles at hatcheries. Using the 88 Sr/ 43 Ca value to determine fish of artificial and natural origin among spawners of autumn chum salmon collected in the Amur River, at salmon hatcheries and base rivers of hatcheries, fish with a high level of the analyzed isotope ratio in the juvenile zone of otoliths were identified, which indicates their artificial origin. Among the fish from the Anyui and Udinsky hatcheries, the majority of fish (56,0 and 56,4%) are characterized by marker values above the threshold, which also indicates their artificial origin. In addition, a high proportion of such fish was found among the individuals of autumn chum salmon collected in the Amur mouth (40,2%). We obtained similar results using another method for assessing the return – the method of otolith marking of juveniles at the hatcheries (in 2015–2021) and the subsequent search for «factory» fish in a mixed sample of spawners from the lower reaches of the Amur River in 2019–2023. It should be noted that in the base rivers of the hatcheries, on the spawning grounds of autumn chum salmon located upstream from the hatcheries, the proportion of fish of hatchery origin was also identified (Anyui River – 37,9%, Gur River – 11,1%). The obtained results may indicate the effectiveness of using microchemical analysis of otoliths to identify the return of autumn chum salmon, the young of which are released from the hatchery, and also determine the need for continuing research in this direction.