Abstract

Salmon lice (Lepeophtheirus salmonis) infestations are the most important constraint to Atlantic salmon (Salmo salar) aquaculture in Norway today. The development of resistance to the most commonly used chemotherapeutants has underlined the need for non-chemical control strategies. One such measure is the adoption of discrete management zones, in which aquaculture operations in all sites, such as stocking, fallowing, treatment and harvesting, are coordinated in distinct areas within each zone. The aim of this project is to investigate the trends of infestation pressure and of lice population growths outside, and within two management zones, one in Trøndelag, and one in Hordaland and Rogaland. The methodology included the analysis of historical data as well as modeling techniques. The results show that inside the zones with coordinated management, the infestation pressure increases throughout the production cycle when the biomass increases, as expected. However, the infestation pressure in the beginning of a production cycle is higher than expected when the biomass inside the zone is low, suggesting that infestation pressure from the neighboring areas with high biomass affects the fallowed area significantly. This effect seems to be more evident in the Trøndelag zone. As the production cycle progressed, larger numbers of sea lice are recorded within the zones than outside them, and there does not seem to be any positive effect after the coordinated practices started. The authors conclude that the zone structure might not be optimal, and in some cases even deleterious rather than beneficial. Further research is needed on the effects of zoning, including simulations of alternative zoning structures and buffer zones between them.

Acknowledgements

The author would like to thank the Norwegian Veterinary Institute and the Norwegian government for the funding and support provided.

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