MODELING FOR DECISION MAKING OF SITING AND MANAGEMENT IN NORWEGIAN AQUACULTURE  

The aquaculture industry in Norway is dominated by salmon farming. Approximately 800 farm locations are distributed along the Norwegian coast where the water temperatures are favorable and vary between typically 5 and 20 ^oC. Each salmon farm can contain several hundreds of thousand individuals, and the necessary feeding is massive.

A major sustainability issue in salmon aquaculture is on farmed fish acting as hosts for the natural parasite salmon louse. With more than 500 times farmed salmon compared to wild salmonid fish, salmon lice have become a potential problem for the latter. The salmon lice have a pelagic phase of many days, and can potentially be spread widely around. The salmon lice can be viewed as particulate material in the water masses, but in addition to a passive horizontal drift with the variable currents they will have a vertical behaviour depending on factors as light, turbulence, temperature and salinity.

The release of waste products from the salmon farms can be large, and will mainly be in the form of particulate material too of various sizes with different sink rates. The waste particles have no swimming capacity as the salmon louse, so the model formulation is simpler.

For both organic waste and salmon lice a particle dispersion model can be used to determine the regional distribution. Critical information will be current and hydrography as well as the source terms of particular organic material or the number of hatched lice.  The Institute of Marine Research operates a modeling systems designed for both salmon lice dispersion and organic waste, where a current model system produces input to the particle tracking model. The difference in model formulation between salmon lice and organic waste will be how we incorporate vertical particle behaviour.

The results from the model experiments are used to optimize farm locations in a geographical perspective, ie. regions ranging from local scale and upwards. Sustainable growth of aquaculture, which is an expressed goal of the Norwegian authorities, is limited by the potential negative influence on the environment and natural ecosystem. We will demonstrate how the modeling system is used for both operational assessment of regional infestation pressure from salmon lice in Norway, as well as how we can estimate the benthic influence area of organic waste in an area with several large salmon farms.