Sex-specific growth in invasive pink salmon (Oncorhynchus gorbuscha) from two regions in northern Norway

The recent invasion of pink salmon (Oncorhynchus gorbuscha) along the Norwegian coast has raised significant ecological concerns. Investigating regional differences in marine growth is an important step in evaluating the establishment of pink salmon in new environments. Pink salmon were captured in two northern Norwegian fjords during their return migration to in the summer of 2023; Varangerfjord in Finnmark and Oksfjord in Troms, representing the eastern and western extent of the core areas of the pink salmon invasion. Body size estimates (total length, weight, condition factor) were used to identify differences in sex-specific marine growth at the time of capture. Scales were analyzed to estimate marine somatic growth via the distance between circuli and the position of the last winter circuli (LWC). Estimates of cumulative circuli distance were divided into four marine growth periods that roughly correspond to 1) spring/summer, year one, 2) summer/fall, year one, 3) fall/winter, year one, and 4) spring, year two. Sex-specific and location effects were found in the body size of pink salmon, where males were heavier and had higher body condition than females and Varanger males had the highest estimates of body size. Scale readings revealed that growth rates were highest in the spring of both years (periods 1 and 4), with significantly decreased growth in the fall/winter (periods 2 and 3). Males from the established Varanger location exhibited the highest growth (17-21% total cumulative circuli distance) over all periods compared to the other groups, suggesting that these fish experience more favorable survivorship and marine growth conditions. These insights into pink salmon marine growth emphasize the importance of taking sex and location into consideration in further assessing the species' expansive potential in Norway.