De Europese meerval in Nederland: van ijstijdrelict tot klimaatopportunist

De Europese meerval (Silurus glanis) is een warmteminnende roofvis die door zijn enorme bek en maximale lengte van bijna drie meter tot de verbeelding spreekt. In de eerste nummers van het RAVON-tijdschrift verschenen drie artikelen over de soort, waarin onder andere werd ingegaan op het voorkomen in het Haarlemmermeergebied en de eerste tekenen van een opmars in andere delen van Nederland. Inmiddels is de soort geen zeldzaamheid meer en wordt deze op steeds meer plaatsen gevangen. Tijd om de balans op te maken. In dit artikel beschrijven we de ontwikkelingen op basis van ruim 150 jaar vangstgegevens en geavanceerde DNA-analyses European catfish in the Netherlands: from ice-age relict to climate opportunist Fossil bone remains indicate that in prehistoric times, European catfish (Silurus glanis) already occurred in what is now the Netherlands. Rising sea levels and the Little Ice Age caused the species to disappear, with the exception of present-day Haarlemmermeer in North Holland. This lake was drained in 1852, but catfish did survive in the Westeinderplassen and other water bodies nearby. Since the 1960s releases of farmed catfish have occurred with increasing regularity (based on source material from Hungary, among others), causing the species to appear in ever more places in the Netherlands. Finds in the great rivers have been followed by occurrences in connected streams. Catfish from elsewhere have been introduced in the Westeinderplassen as well; they have crossbred with the original relict population, which had become genetically depauperate. The purely relict animals apparently can no longer reproduce with each other due to inbreeding. The hybrids do have breeding success with each other, causing the species to increase in numbers here as well. The European catfish is adapted to live in relatively warm waters, which means that thanks to climate change it can now reproduce better in the Netherlands. The presence of staple foods such as exotic gobies and crayfish may also be a factor, and it is to be expected that this species will spread further in the future.