Protecting the health and survival of wild salmon populations is a main objective of sea-lice regulation for salmonid farming. This study has evaluated the environmental effectiveness of sea-lice regulation setting strict thresholds for the average number of lice per farmed fish in Norway. From an environmental perspective, the success of such regulation does not depend on the average number of lice per salmon in the net pens, but on the degree to which compliance contributes to lessening the mortality risk for surrounding wild salmonid populations—and thus, ultimately, the wild salmon population survival. Since the 1970s, the proportion of wild Atlantic salmon returning to Norwegian rivers has been almost halved, while Norwegian salmon farming has undergone massive industrialization and expansion. As the proliferation of sea lice may be an important part of the explanation for the decline in wild salmon, Norway has enacted increasingly stricter regulatory thresholds for the average number of lice per farmed fish at production sites.
This study shows that practicing a stricter lice threshold reduces the average number of lice per fish within farming sites. Thus, the strict regulation has had positive effects on lice-levels at production sites . However, more frequent de-lousing measures to ensure compliance leads to farmed-salmon welfare problems and higher mortality rates in the net pens (Fig. 1). Furthermore, the analysis shows that the environmental effectiveness of the regulation has been limited or absent: successful compliance with stricter thresholds has not lessened the sea-lice infestation pressure on surrounding, wild salmonid populations. The environmental effectiveness of such regulation is thus limited. This raises the important question of whether a regulatory regime focused on minimizing the average number of sea lice per farmed fish may do more harm than good, unless accompanied by a broader set of regulatory instruments targeting other variables that affect sea-lice infestations in the wild salmon habitat.