De opkomst van de Europese meerval

De grootste inheemse roofvis van Nederland is inmiddels geen onbekende meer. Omstreeks 1950 was deze zoetwaterreus bijna uitgestorven in Nederland en kwam waarschijnlijk alleen nog in het Haarlemmermeergebied voor. De laatste jaren komen er echter steeds vaker vangstmeldingen vanuit de sport- en beroepsvisserij. Meldingen en waarnemingen van vissen groter dan twee meter nemen toe. Daarmee ook de verhalen van mysterieuze verdwijningen van onder andere watervogels en kleine hondjes. Kortom: het gaat goed met de Europese meerval (Silurus glanis) in Nederland. Sportvisserij Nederland heeft verschillende onderzoeken uitgevoerd om als onderdeel van het visstandbeheer meer te weten te komen over de populatiegroei, het verspreidingsgebied en de leefwijze van deze toppredator in Nederland. After a century of near absence, catch reports of the European catfish (Silurus glanis) have increased tremendously due to the improved water quality and the redesign of riverbanks. Today, this fresh water giant has recovered, renewed and spawned immensely, which even results in catch reports of catfish larger than 2 meters. Another big contributor to the resurrection of the catfish is the climate change. Catfish thrive by warmer water conditions. Since 1910, the temperature of the river Maas has increased by an average of 3 °C. Also introductions and escapes from hatchery probably play a roll.The catfish are mainly concentrated in the largest rivers in the country, and the area around the Haarlemmermeer, Oude IJssel and Flevoland. Approximately 60% of all records originate from a dammed section of the river Maas between Linne and Roermond. The Royal Dutch Angling Association conducted research in the river Maas, Westeinderplassen and Oude IJssel to obtain data on the movements, behaviour and habitat use of individual catfish by using a combination of acoustic and transponder technologies. All fish remained in the studied area throughout the surveyed period. Striking was that the catfish clung to specific sections of the studied areas containing artificial (in the form of moored boats) or natural (floating reed beds) covered water areas. Catfish proved to be most active at night (after sundown till the morning) and least active during midday (11-15h). Activity of catfish was also highly dependent on watertemperature, with no signs of activity at temperatures below 7 °C and most activity at watertemperatures 10 °C or higher.