Distribution of Atlantic salmon ( Salmo salar ) from epipelagic trawling surveys and genetic analysis in Scotland

Abstract This study investigates the spatial distribution and migratory patterns of Atlantic salmon (Salmo salar) post-smolts in the coastal waters of the east coast of Scotland and the North Sea. Using epipelagic trawling surveys conducted over 4 years (2017–2021), 1020 Atlantic salmon post-smolts were captured. The spatial distribution of salmon post-smolts was highly variable, with the highest catch rates observed in three key areas: the southern edge of the Moray Firth, the east coast of Scotland from the River Ythan to the River Tweed, and the area east of Fraserburgh, ∼100 km from shore. No post-smolts were captured in the northern part of the Moray Firth. Genetic Stock Identification (GSI) was used to assign 926 of the salmon post-smolts to their river or region of origin, with 86% of the fish assigned to the ‘East coast’ region. The distribution of genetically assigned fish suggests that salmon post-smolts from different rivers exhibit region-specific migratory patterns, with individuals from the Moray Firth region migrating primarily eastwards, followed by a northerly trajectory. The results highlight the importance of specific marine areas as migration corridors for Atlantic salmon post-smolts, with implications for the conservation and management of migratory salmon populations, especially in light of increasing marine renewable energy developments. This study provides a novel contribution to the understanding of early marine migration patterns of Atlantic salmon in the North Sea, offering essential data for future conservation strategies aimed at protecting these species during their vulnerable early marine life stages. Additionally, it underscores the utility of epipelagic trawling and genetic analysis in mapping migration pathways and understanding fish distribution in offshore environments.