Validation of geographical influence of aquaculture

The numerical model that today is used to calculatethe dispersal of salmon lice, both for scientific and advisory purposes, has ben expanded to track organic waste from farm sites to evaluate the influenced area at the sea bed. Resuspension has ben included by assuming that particles it being transported along the sea bed when the velocities exceeds a critical velocity. As the particles is being transported with the currents along the seabed the predicted footprint at the seabed is estimated to be larger at the coast compared to more farm sites in more sheltered fjord arms. The model calculates the geographical distribution of organic material from fish farm based on maximum allowed biomass. The organic enrichment is greatest close to the farm site, but there exists local convergence zones. The organic enrichment close to the seabed seldom exceeds the natural background levels in the area beyond 500 m distance from the farm. The model predicts low concentrations of organic matter to be dispersed to areas of many square kilometers. These low concentrations will be hard to detect directly, but organic matter potentially contains therapeutic chemicals and terrestrial sorced fatty acids that might be detected in smaller levels.

The aim of this project is to improve the dispersion model used to calculate the influence area from aquaculture farms with respect to salmon lice. The dispersion model is suitable to track organic waste from selected farm sites, but does not include realistically resuspension, breakage and decay of organic particles or biomineralisation of organic particles. By including these parameters and differentiating between differnt bottom types (hard, mixed and soft substrates) the model will be able to generate more realistic predictions of the distribution and accumulation of organic matter (potentially containing therapeutic chemicals and terrestrial sorced fatty acids) from fish farms. As the model is generic and can be used for any fjord/area along the Norwegian coastline it will be used to simulate dispersion from multiple farms in an area. Convergence zones with strong impact of aquaculture will be mapped, both with respect to organic matter and salmon lice. By comparing the model output to observations retrieved in existing projects the importance of the convergence areas will be evaluated.