To estimate the salmon lice infection pressure in the fjords and along the coast during the smolt migration, an annual survey is conducted to assess the presence of sea lice on wild salmonids. Three methods are used, trawling for salmon postsmolts using a surface trawl in Boknafjorden, Hardangerfjorden, Sognefjorden, Nordfjord, Romsdalsfjorden and Vågsfjord. In addition, sea trout and Arctic char are captured using nets and traps in all 13 production areas, and sentinel cages stocked with farmed salmon postsmolts are deployed in Hardanger and Sognefjorden.
Trawl data still show the highest infestation of sea lice on wild migrating post-smolts of salmon in Hardanger and Sognefjorden, where sea lice-related mortality is estimated to be > 30%. Estimated sea lice-related mortality was lower but still has a significant impact in Boknafjorden, Nordfjord, and Romsdalsfjord, with sea lice-related mortality ranging between 10 and 30%. In Vågsfjord, there was little lice on the salmon, and it is estimated to have low (< 10%) mortality. However, in Vågsfjord trawling was done relatively close to the rivers flowing into the fjord, which means that the data likely underestimate the lice infestation on the fish. In each of the fjords, there were variations both in time and between regions where the fish migrated from.
Trap data indicate a similar pattern to trawl data but consistently show more lice on the fish. Roughly, there is considered to be a high sea lice-related mortality in all production areas from PO2 (Rogaland) to and including PO7 (Trøndelag). There are fewer lice on sea trout and Arctic char further north, but there is variation within the production areas in space and time. In Sørlandet, there was little sea lice on sea trout.
Cage data from Hardangerfjorden show a moderate infection pressure in the central parts during the 2-week period from the midpoint of migration, which is extended somewhat in the following 2-week period. In Sognefjorden, there was a moderate number of lice at the two innermost cage stations near the border of the national salmon fjord in both of these periods, while there was low infection pressure in the outer areas.