Veranderingen in de prikkenpopulatie in de Niers

Changes in the lamprey populations in the river Niers A population of both brook lamprey (Lampetra planeri) and river lamprey (Lampetra fluviatilis) occurs in the river Niers in the Netherlands. Based on a study in 2013 and 2021, the density and distribution of larvae shows a strong decline. The length frequency distribution implies that an annual reproduction is still taking place. At one site the spawning of lampreys is monitored since 2007. Since 2015 no spawning lampreys have been observed here. Data of another monitoring programme indicate fluctuations in the population size. Whereas in a small tributary, a brook lamprey population is increasing in response to improved habitat quality. Several factors seem to influence the lamprey population in the river Niers, both negative and positive. Optimistische woorden klonken er in 2014 nog over de prikken in de Niers. Onderzoeksresultaten wezen op een ‘florerende populatie’ en een ‘zonnige toekomst’. Acht jaar later is het onderzoek van destijds overgedaan en komen we tot andere conclusies. De dichtheid en verspreiding zijn flink afgenomen. Wat is er aan de hand met de prikken in het Nierssysteem?