Improved Technology for the Application and Detection of Rotenone in Large and Deep Norwegian Lakes

The introduction of the salmon parasite Gyrodactylus salaris to Norwegian rivers has led to massive mortality of juvenile salmon (Salmo salar) in affected rivers. In the Vefsna watershed in Northern Norway the infection spread within the region to finally comprise 10 watersheds. Further examination led to the discovery of the salmon parasite on Arctic char (Salvelinus alpinus) in three lakes. The addition of these lakes in the eradication project made it one of the world’s most extensive rotenone treatments.

The lakes totalled 18.5 km², with depths of 65 meters, and 30 km of anadromous tributaries. GEMSS modelling of rotenone application scenarios pointed to a quick rotenone distribution on both sides of the thermocline to achieve a homogenous distribution of rotenone. It was important to avoid pockets of untreated water that could be sustained by tributaries.

Custom built equipment made it possible to achieve homogenous rotenone distribution within 2 days. A system for simple and accurate liquid chromatography with UV-detection was used for the on-site determination of rotenone from water samples, producing analysis results within a few hours after sample collection.

Parallel to the eradication programme, extensive work relating to conservation of native fish stocks were performed.