The Status of the Chum Salmon (Oncorhynchus keta) Commercial Stock and Prediction of its Size off Iturup Island

Abstract

The abundance dynamics and the size and age structure of the chum salmon stock formed in Prostor and Kurilsky Bays of Iturup Island, Kuril Islands have been analyzed. The number of chum juveniles released into the waters of the bays increased from 10.7 million fish in 1996 to 197.6 million fish in 2020. The catch of adults was closely related (r = 0.66) with the release of juveniles and also increased from 800 t in 1996 to 18 968 t in 2019. The year-to-year dynamics of the chum salmon catch was almost identical between these two bays. If a strong year-class formed, it was caught in both bays; with a low survival rate of a year-class, low catches were recorded everywhere. Spawners of younger age groups (aged 2+ and, predominantly, 3+ years) markedly dominated catches in 2014–2022. Of 22 939 spawners examined in those years, 14 221 fish, or 62.0%, were aged 3+ years. Prediction of chum salmon catch weight in Prostor and Kurilsky Bays is based on two factors: the substantial predominance of age 3+ spawners in each year-class and the close correlation between the catch at age 2+ and the catch at age 3+ in the following year (r = 0.89; r_s = 0.98). The significant relationship between the catch of pink salmon and that of chum salmon spawners at age 3+ from the year-classes of juveniles released in the same year (r = 0.71; r_s = 0.75) can be considered an additional criterion.