Estimation of Outmigrating Juvenile Pink Salmon Abundance in Rivers of the Sakhalin and Iturup Islands in 2024

The pink salmon is the main target species of salmon fishery in the Sakhalin–Kuril region. To forecast its stock abundance, assessment of juvenile pink salmon outmigration is especially important because it reflects the year-class survival rate from post-spawning to sea entry. This report provides the results of a quantitative estimation of outmigrating juvenile pink salmon abundance in rivers including the Dagi, Malaya Khuzi, Pugachevka, Voznesenka, Ochepukha, Taranai, and Kura on the eastern Sakhalin coast, the Rybatskaya and Olya in Iturup Island, and the Kholodny Stream (a tributary of the Poronai River). The downstream migration index was calculated as the ratio of number of spawners that entered rivers to the number of their outmigrating progeny for all reference rivers mentioned above. The number of wild juveniles that outmigrated from all rivers was calculated based on data on abundance of pink salmon spawners in rivers and the downstream migration index. For the eastern Sakhalin coast, such calculations were performed separately for each regional unit of pink salmon spawning stock. In 2024, the total number of pink salmon outmigrants was estimated as 1044.5 million fish from the eastern Sakhalin coast and 16.1 million fish from Iturup Island. In addition to these numbers, 101.8 million and 28.1 million fish of this salmon species were released from salmon hatcheries, respectively.