Sammendrag
Salmon lice are external parasites on salmonids in the marine environment. During recent years, sea lice
abundance has been increased due to the presence of salmon farming using on-growing floating seas-cages. Amongst
salmonids, sea trout is especially vulnerable to salmon lice infestations, because during their marine residence they
typically remain in coastal waters, where open net cage Atlantic salmon farms typically are situated. In this report the
existing knowledge about the effects of salmon lice on sea trout populations in the NE Atlantic coastal waters has been
reviewed, assessing the current situation of this problematic. Salmon aquaculture increase the salmon lice abundance,
which affect negatively on sea trout populations as an increase in marine mortality, changes in migratory behaviour and
reduction of marine growth. These conclusions are based on published studies that range from those investigating the
effects of salmon lice on individual fish, both in the laboratory and the field, to analyses of their impacts on populations
in the wild. In sum, the combined knowledge from the reviewed studies provides evidence of a general and pervasive
negative effect of salmon lice on sea trout populations, especially in intensively farmed areas. The effects induced by
elevated salmon lice levels inevitably imply a reduction in numbers and body size of sea trout returning to freshwater for
spawning, affecting the local population dynamic and recreational and commercial fisheries in the most impacted areas.
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