Marine growth of introduced pink salmon (Oncorhynchus gorbuscha) caught in northern and central Norway

Abstract

The introduction of pink salmon in the White Sea area during the second half of the 20th century has resulted in the establishment of a self-sustaining population of pink salmon in rivers draining to the Barents Sea and North Atlantic Ocean. The size and abundance of pink salmon is dependent on survival during the marine phase, where they acquire more than 95% of their body weight. Investigating marine growth of pink salmon caught in Norwegian rivers is important to understand population dynamics, and their geographical expansion and variation in abundance and size over time. The aim of this study was to investigate how early marine growth affect adult size of pink salmon caught in Norwegian rivers prior to spawning. Scales from pink salmon caught in the river Skallelva in Finnmark county in 2019 and 2021, and scales from pink salmon caught in Central Norway in 2021, were used in scale analyses to compare annual, seasonal and regional growth characteristics. Scale analyses of pink salmon in this study showed that fish entering Norwegian rivers in 2021 seemed to have had better growth conditions from sea entry to the winter, compared to fish entering rivers in 2019, despite large individual variation. The growth pattern showed a short period of reduced growth during summer and early autumn that was characteristic in fish caught in both Skallelva in 2019, Skallelva in 2021 and Central Norway in 2021. This seems a typical trait of growth in pink salmon when they are believed to stay in coastal areas and has been described for pink salmon native to the Pacific Ocean. During autumn the growth increased and stabilized before a pronounced period of reduced growth during winter. The autumn and winter growth had more effect on fish size at river entry than the first period of marine growth. This study is the first to provide detailed information about scale growth in pink salmon between years and regions. The results from this work is important in understanding early growth in pink salmon and what may affect their size as adults entering Norwegian rivers to spawn.

Pink salmon - scale analysis - growth patter - winter zone - Atlantic Ocean