Reintroduction of Brook Lamprey (Lampetra planeri) in a Lowland Stream and Evaluation of Its Success

Brook lamprey (Lampetra planeri) became extinct in much of its former range in the south of the Netherlands. A reintroduction project from 2014 until 2018 aimed at the reestablishment of a population in the Reusel stream. Every year just over 1000 individuals (96% larvae, 4% adults) were translocated from the nearest population. Monitoring reveals that donor population was not jeopardized. The new population reproduces, larvae densities increased to >2 individuals per square meter in (sub) optimal habitat, larvae occur in different age groups and the distribution range expanded to 5 km. In 2024 the population is at the point of self-sustaining through natural reproduction. The new population judged by size, range and demographics is currently estimated to be ‘Vulnerable’, based on IUCN criteria. Due to a high probability of impact of droughts and therefore an increased extinction risk, the best available integrated estimate of population status would be ‘Endangered’. Monitoring remains essential to keep track of the development of the brook lamprey population and in steering ‘post reintroduction management’. The water system showed to be highly sensitive to progressive impacts from climate change and intensive land use. Further restoration of the watershed is extremely important to both nature and agriculture.