AEI 7:91-113 (2015)  -  DOI: https://doi.org/10.3354/aei00142

REVIEW
Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta—a literature review

Eva B. Thorstad1,*, Christopher D. Todd2, Ingebrigt Uglem1, Pål Arne Bjørn3, Patrick G. Gargan4, Knut Wiik Vollset5, Elina Halttunen3, Steinar Kålås6, Marius Berg1, Bengt Finstad

1Norwegian Institute for Nature Research, 7485 Trondheim, Norway
2University of St Andrews, St Andrews, Fife, KY16 8LB, UK
3Institute of Marine Research, 9294 Tromsø, Norway
4Inland Fisheries Ireland, 3044 Lake Drive, Citywest Business Campus, Dublin 24, Ireland
5Uni Research Environment, 5006 Bergen, Norway
6Rådgivende Biologer AS, 5003 Bergen, Norway
*Corresponding author:

ABSTRACT: Salmon farming increases the abundance of salmon lice, which are ectoparasites of salmonids in the sea. Here we review the current knowledge on the effects of salmon lice on wild sea trout. Salmon lice feed on host mucus, skin and muscle, and infestation may induce osmoregulatory dysfunction, physiological stress, anaemia, reduced feeding and growth, increased susceptibility to secondary infections, reduced disease resistance and ultimately mortality of individual sea trout. Wild sea trout in farm-free areas generally show low lice levels. In farm-intensive areas, lice levels on wild sea trout are typically higher, and more variable than in farm-free areas. Lice on wild sea trout are found at elevated levels particularly within 30 km of the nearest farms but can also extend to further ranges. Salmon lice in intensively farmed areas have negatively impacted wild sea trout populations by reducing growth and increasing marine mortality. Quantification of these impacts remains a challenge, although population-level effects have been quantified in Atlantic salmon by comparing the survival of chemically protected fish with control groups, which are relevant also for sea trout. Mortality attributable to salmon lice can lead to an average of 12-29% fewer salmon spawners. Reduced growth and increased mortality will reduce the benefits of marine migration for sea trout, and may also result in selection against anadromy in areas with high lice levels. Salmon lice-induced effects on sea trout populations may also extend to altered genetic composition and reduced diversity, and possibly to the local loss of sea trout, and establishment of exclusively freshwater resident populations.


KEY WORDS: Salmon lice · Lepeophtheirus salmonis · Sea trout · Salmo trutta · Parasite · Aquaculture · Salmon farming


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Cite this article as: Thorstad EB, Todd CD, Uglem I, Bjørn PA and others (2015) Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta—a literature review. Aquacult Environ Interact 7:91-113. https://doi.org/10.3354/aei00142

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