Salmon lice can influence both growth, survival and behavior of sea trout, according to an extensive, international literature review.
Sea trout. Photo: Eva Thorstad / NINA.
In collaboration with leading scientists from Norway, Ireland and Great Britain, scientists from NINA (Norwegian Institute for Nature Research) have reviewed current knowledge on the effects of salmon lice on wild sea trout. The review was recently published in the high ranked international journal Aquaculture Environment Interactions, and can be downloaded in full text here.
Influences growth, survival and behavior
– We have examined the effect of salmon lice on wild sea trout based on Norwegian and international studies, and shown that elevated lice levels in farm-intensive areas have negative effects on both growth, survival and behavior, says NINA researcher Bengt Finstad, who has led the work.
Only some of the brown trout migrate to the sea. The migrant sea trout usually grow larger and have more eggs than the non-migratory trout, but reduced growth and survival due to salmon lice will reduce the benefits of marine migration for sea trout. This might lead to selection in favor of non-migratory trout in areas with high lice levels, and hence fewer migratory sea trout.
Can affect the trout fisheries negatively
Less migratory sea trout due to salmon lice might not sound dramatic, but it might result in reduced future recruitment of trout and reduced or eliminated harvestable surplus of trout for fisheries.
In some locations, a high level of salmon lice might even lead to the local loss of sea trout, and establishment of exclusively freshwater resident populations. Populations living in small rivers with unstable environmental conditions during parts of the year, which are dependent on sea migration to survive during these periods, are in danger of disappearing.
Distance to farms important
Wild sea trout in farm-free areas generally show low lice levels. Elevated levels of lice are particularly found within 30 km of the nearest farms, but in some cases also further away.
– It was the salmon farming industry that asked for this literature review, and the study was funded by the Norwegian Seafood Research Fund (FHF), says Finstad.
Contact person: Bengt Finstad (NINA)
Read more: Effects of salmon lice Lepeophteirus salmonis on wild sea trout Salmo trutta – a literature review