Technical and Political Challenges Facing Gyrodactylus Salaris Control in River Vefsna, Norway

The salmon parasite Gyrodactylus salaris is among the worst threats to Atlantic salmon (Salmo salar). In infected rivers, the local salmon stock will be extinct within a few years. In an attempt to restore affected river systems, Norwegian authorities treat infected rivers with rotenone to remove infected fish. The parasite cannot survive without the host and cannot survive in seawater. In 2011-2012 a rotenone project is planned in the Vefsna region. In this project ten infected rivers have to be treated within a narrow time frame to avoid reinfestation. In addition, the river Fusta drainage, including lake Fustvatnet (10.6 km²), lake Mjåvatnet (2.6 km²), and lake Ømmervatnet (5.4 km²), will need to be treated with rotenone to eradicate the parasite from this region. A lake, the volume and depth (68 m maximum depth) of Fustvatnet, has not been previously treated with rotenone, and there are concerns that rotenone completely mixed throughout the lake and kills all fish. Various scenarios of dosing were simulated by the model Generalized Environmental Modeling System for Surfacewaters (GEMSS). The simulations obtained satisfactory concentration in the lake. The treatment strategy with the best chance of success is to use the fall turnover and dropping surface water temperatures to assist with rotenone mixing in the lakes. Big lakes have not previously been treated with rotenone in Norway. For this reason the project has big challenges relating to both technical solutions, political and public acceptance and funding. The total expenses for the rotenone treatment are estimated to 20 millions USD.