The first data from non-commercial monitoring of the occurrence and range of river lamprey, Lampetra fluviatilis, in selected rivers in northern Poland

Human impact on fish populations extends beyond mere exploitation. Rivers and streams, essential conduits for these fish migrations, have undergone substantial anthropogenic modifications driven by navigation, hydropower generation, and water regulation imperatives. An example of one species that has been affected from the anadromous lampreys is river lamprey, Lampetra fluviatilis (L.). Populations of anadromous lampreys have declined dramatically in European rivers, including in Poland, because of the loss of river connectivity and habitat modification that prevents adult lamprey from reaching their original spawning grounds. The present study was conducted on 11 rivers located in northern Poland in the southern Baltic Sea catchment area. River lamprey spawners were sampled with dedicated traps, and 3,026 specimens of 29 fish species were caught at all the sites investigated. The most abundant, frequent species was river lamprey (n = 1,062), which was recorded in 10 of 11 rivers. Only in one case, were river lamprey specimens recorded above a barrage with a fish pass in a tributary of the Rega River. In all other rivers, lamprey was recorded only at sampling sites below the first barrier. Since most fish passes are not designed to provide passage for weaker swimming or non-jumping species, they are not suitable for non-salmonid species like river lamprey.