Gekleurde jonge aaltjes wijzen de weg Onderzoek naar intrek, aanbod en knelpunten langs de Noord- Hollandse IJsselmeerkust

Landward migration of European eel via the coast of Lake IJsselmeer in the Province of Noord-Holland During the spring of 2020, a study was conducted on the landward migration of European eel (Anguilla anguilla) via the coast of Lake IJsselmeer in the Province of Noord-Holland. The main objectives were to gain insight in the magnitude of the migration, the extent to which migration barriers are encountered and how well existing fish passes function. This nowledge is needed to prioritize appropriate measures for the coming years, like constructing or improving fish passes. A selection of the most important connection points in the study area was made, which includes pumping stations and water intake systems, two of which are already equipped with minor adjustments to facilitate fish migration. Depending on the properties of the connection points dfferent study methods were utilized simultaneously, which include lifting nets, glass eel collectors, glass eel detectors, fyke nets, environmental DNA and markrecapture experiments using VIE-tags. At all study sites young eels were caught. The glass eel recruitment to Lake IJsselmeer from the Wadden Sea at Den Oever was estimated to be in the range of 1.3 million (95% CI: 548.596-3.034.492). The total number of potentially landward migrating eels during 2020 at all study sites combined was estimated to be 343.000 individuals (95% CI: 179.000-937.000), the majority being young yellow eels and a smaller fraction being glass eel. Only an estimated 17% of the young eels was facilitated by water intake systems and fish passes to actually migrate landward. The e,ciency of the existing fish passes was very low. Specific recommendations were outlined to facilitate migration of eels at the study sites Het IJsselmeer en de aanliggende Noord-Hollandse polders zijn van oudsher een geliefd opgroeigebied voor aal. Bij de zoektocht oriënteert jonge aal zich op lokstromen afkomstig van spuisluizen en gemalen. In de Afsluitdijk worden steeds meer maatregelen genomen om jonge aal naar binnen te laten, zoals een vispassage bij Den Oever (2015) en sinds dat jaar wordt daar en bij Kornwerderzand ook visvriendelijk sluisbeheer toegepast. In de toekomst gaat ook de ‘Vismigratierivier’ voor betere passeerbaarheid van de Afsluitdijk zorgen. Omdat er steeds meer jonge aal het IJsselmeer in kan trekken, is het van belang om te kijken welke gebieden bereikbaar zijn