Comparative Analysis of Natural- and Hatchery-Origin Chum Salmon Oncorhynchus keta (Salmonidae) Spawners Identified in Mixed Stock with Otolith Marking

The body length and weight of the hatchery- and natural-origin chum salmon Oncorhynchus keta spawners (identified with the otolith marking technique) in the commercial stock in the Yasnomorka River and the Yasnomorskoe salmon stocking fish hatchery were analyzed in 2015–2019. The proportion of hatchery-origin fish comprised 65.5%, varying from 37.2 to 72.9% from year to year. In addition, 9.2% of specimens had the otolith marks provided by the adjacent salmon stocking fish hatcheries, such as the Sokolniki and Kalinin enterprises. The body weight of the natural- and hatchery-origin chum salmon spawners entered the river for spawning for each age group was not different with a few exceptions. However, the females and males spawn naturally tended to reach the sex maturity at the earlier age, on average, in all their generations for a five-year observation, when compared that to the hatchery-origin fish. Overall, the proportion of fish aged 2+ to 3+ among the hatchery- and natural-origin females comprised 25.1 and 61.5%, respectively. With respect to the hatchery- and natural-origin males, the proportions made up 32.2 and 69.0%, respectively.