The decline in stocks of sea trout, i.e. anadromous brown trout (Salmo trutta L.), on the west coast of
Norway has given rise to a series of conservation measures and highlighted the need for a non-destructive
capturing method. For this reason, a trap was developed for use in marine environments, with the overall
goal of capturing sea trout unharmed and obtaining accurate assessments of sea lice (Lepeophtheirus
salmonis) infection levels. The trap design captured all size classes of sea trout, and a variety of other
coastal fish species, none of which suffered net-induced mortality. The trap was used to compare the
abundance and intensity of sea lice on sea trout captured in that particular trap, as opposed to gillnets.
The abundance of adult sea lice on trout caught in the trap was significantly higher than on trout caught
in gillnets, but not significant for larval sea lice. The intensity of sea lice was only significant for the
total number of lice (adult and larvae). These results indicate that estimated infection levels for trout
captured by gillnets, which are frequently used in assessment programmes for sea lice, are likely to be
underestimated. Consequently, the use of this particular trap can be recommended for the capture of sea
trout for sea lice infection assessments. In general, the trap is an appropriate tool for studies where live,
unharmed, coastal fish are required for research or conservation purposes