Is de grootste beekdonderpadpopulatie van Nederland in gevaar?

Is the largest Rhine sculpin population of the Netherlands at risk? The River Geul is a fast-flowing, cold hillside chalk stream that harbours the largest Rhine sculpin (Cotthus rhenanus) population in the Netherlands. Over the past two decades, the population has recovered as a result of water quality improvements and in the absence of invasive alien gobies. Since 2017, the invasive alien round goby (Neogobius melanostomus) started to colonise the River Geul with an annual rate of 1.2 km. In 2023, its presence has been established beyond a fish migration barrier which means that the Rhine sculpin population is no longer isolated from the round goby. There is a high risk that the establishment of the round goby in the River Geul catchment area will negatively affect the Rhine sculpin population via food and shelter competition. Further research will determine the impacts as well as the capability of the round goby to establish high densities in a fast-flowing, cold hillside chalk stream such as the River Geul In 2018 berichtten we in dit tijdschrift over de eerste invasieve zwartbekgrondel die in 2017 in de Geul werd aangetroffen, circa 300 meter van de monding in de Maas. De Geul herbergt de grootste populatie beekdonderpad van Nederland en was tot die tijd vrij van zwartbekgrondels. Het risico van potentiële negatieve effecten van de zwartbekgrondel op de beekdonderpadpopulatie wordt als zeer hoog ingeschat. Daarom is de kolonisatie nauwlettend gevolgd. In dit artikel beschrijven we onze bevindingen.