Abstract
In the Baltic Sea Basin, the river lamprey, Lampetra fluviatilis (L.), is still important to commercial fishing; however, the species is on the decline, especially in the southern part of the catchment area. At present, the river lamprey is protected by European law that requires monitoring its stocks. This article describes a convenient trap for catching adult river lamprey in streams. The gear is a small fish-pot or hoop-net with two chambers. Operating the trap is very simple, and tests indicated its usefulness for monitoring ascending river lamprey. Thus, this trap design is recommended as a standard tool for use in the future, especially since there is a lack of commercial fishery data.