The electrofishing boat is used to map the fish resources in rivers where traditional methods are insufficient.
The electrofishing boat is used to map and monitor fish populations in large rivers. Photo © NINA
Normally fish are caught and counted using gillnets, or handheld electrofishing equipment. Gillnets are poorly suited for use in rivers with strong currents. In addition the use of gillnets entails high fish mortality. Meanwhile, normal electrofishing is only suitable for use in the shallow parts of rivers. As a result, our knowledge about the deeper parts of Norwegian rivers is limited. For instance, we know very little about the importance of these areas for the production of fish. With the electrofishing boat we are now able to reach these areas, which have previously been too deep and inaccessible. Hence, we can gain important knowledge about where the fish are located during different life stages, and how large different fish populations really are.
An effective and benign survey method
The electrofishing boat is equipped with electrodes, which attract the fish by creating an electric field of up to 1000 volt around the boat. The fish is given just enough electricity to be stunned for a few seconds. That is enough for us to catch it with a dip net and place it in a tank on board the boat. There we can count, measure, weigh, and examine the fish in other ways, before we release it again. This is thus a benign survey method. The registered fish mortality is below 1%, and much below other catch methods.
There is always a certain risk involved when translocating vessels between different lakes, rivers, and streams. To avoid spreading undesirable organisms NINA, in collaboration with veterinaries and other experts, has developed methods and routines for disinfecting the electrofishing boat before its’ translocation to new areas. As part of this procedure we run a disinfectant through the cooling system of the engine and the generator.
The most important users of the research services that NINA can offer with the electrofishing boat are local, regional, and national wildlife managers, hydropower companies, and landowners.