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Dryad

Parasite scars: The impact of salmon lice injury on sea trout populations

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Oct 14, 2024 version files 28.17 KB

Abstract

Spillback effects of the parasitic salmon louse from fish farms to wild fish are a critical environmental concern for salmon-producing countries. This ectoparasite causes significant physiological damage to wild salmonids. However, strong empirical links between injuries and abundance lice has not been established in situ. This study empirically establishes a strong association between dorsal fin damage in sea trout (Salmo trutta) and infestation with mobile stages of salmon lice at a marine site. We further assessed the prevalence of such damages on returning sea trout to the spawning grounds through snorkelling observations in 16 rivers in Hardangerfjord, western Norway, from 2007-2021. The prevalence of injuries decreased with distance from the fjord outlet, from ~70% in middle and outer parts to ~10% in the inner parts. Additionally, a negative correlation was found between sea trout population size and the proportion of the population with dorsal fin damage. The results demonstrate that salmon lice inflict high levels of injury on significant portions of sea trout populations in areas with intensive fish farming, leading to poorer population status in affected populations.