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Aquaculture Environment Interactions

    AEI prepress abstract   -  DOI:

    The impact of variable physical conditions and future increased aquaculture production on lice infestation pressure and sustainability in Norway

    Mari S. Myksvoll*, Anne D. Sandvik, Ingrid A. Johnsen, Jofrid Skarðhamar, Jon Albretsen

    *Corresponding author:

    ABSTRACT: Salmon lice infestation is a challenge for wild post-smolt salmon during their migration from the river to the sea in several regions of Norway. The traffic-light management system regulates growth in the aquaculture industry, where growth in production (6%) is only allowed if the impact of salmon lice on wild fish is considered sustainable. We have used a numerical ocean model, combined with an individual-based model for salmon lice, to evaluate the interannual variability in salmon lice concentrations in Production Zone 7, which was granted growth in 2017. The salmon lice releases were kept constant for 3 yr, while the physical conditions, e.g. wind and ocean circulation, varied. The total area of elevated lice infestations varied between 3.2 and 8.4% of the area within 5 km from the coast, due only to interannual physical variability mainly caused by variable wind patterns. Modeled post-smolts migrating out from the Namsen river (64.5°N, mid-Norway) towards the open ocean experienced mortality between 5 and 9%. Since Production Zone 7 was granted growth, we simulated increased production and corresponding increase in lice releases as the production grew. After 5 to 8 increments of 6%, the increase in salmon post-smolt mortality was of the same order as the interannual variability. Mortality in post-smolts was highly dependent on information regarding migration route and time. These 2 methods (area of elevated lice infestations and post-smolt mortality) provide complementary information and should be used in combination when the overall assessment of a production zone is made.