EAA Netherlands updated research finds that catfish population has increased and spread throughout the Rhineland region

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16 Apr

EAA Member Sportvisserij Nederland and the Rijnland Water Board conducted new joint research regarding catfish population throughout Rhineland region. This as in recent years, there have been various signs that the Westeinderplassen catfish population has been growing and spreading further over the wider area.

Several studies on the catfish species dating from 2012 and 2013 pointed out that the population in the ‘Westeinderplassen’ region was relatively sedentary. Also, the population in question deviated genetically from congeners from the Maas and Oude Ijsel rivers.

10 years after this first research on the species in the Westeinderplassen EAA Member Sportvisserij Nederland – together with Rijnland Water Board – conducted a joint research to assess the state of play of the species in the region.

To determine the current population size of this lake area near Aalsmeer, a so-called brand capture study was set up in early 20221. For the research, professional fisherman Theo Rekelhof helped – just as in 2012-2013 – with catching the necessary catfish from mid-May to the end of August. A PIT (Passive Integrated Transponder) tag was installed in each caught catfish by qualified EAA Netherlands representatives. These PIT-tags contain information, making the catfish individually recognizable. Based on the ratio between the number of tagged and untagged specimens that were caught later, an estimation was made of the size of the catfish population in the Westeinderplassen.

Results of the study

During the study period, a total of 444 unique catfish between 7 and 154 cm (length) were caught, with the heaviest specimen weighing around 25 kilograms. The distribution of catfish in the Netherlands has increased further since 2011, with a 44% increase.

The total number of catfish in the Westeinderplassen that is larger than 25 cm is estimated at more than 3,200 individuals, which is 4 times more than 10 years ago. The length-frequency distribution of the population shows that there is a clear peak between 30 and 50 cm. All this indicates a healthy and natural build-up of the stock in the Westeinderplassen. Furthermore, it appears that catfish in Rhineland region does not (yet) reach the gigantic sizes of more than two meters – which have already been caught elsewhere in the Netherlands.

This 'heatmap' clearly shows the distribution of catfish across the Rhineland area.

Register of catfish catches

Through citizen science, EAA Netherlands has collected as many catfish catches as possible to be able to map the distribution of catfish throughout the whole Rhineland region. Following several appeals to anglers, 107 catch reports were received from the specific area via www.meervalmeldpunt.nl.

The sport fishing community MijnVISmaat also yielded 64 catches in the working area of Rhineland. Thanks to all this data, it has become clear that the catfish no longer only occurs in the Westeinderplassen and adjacent Ringvaart of the Haarlemmermeerpolder.

Dissemination of the catfish population

Over the past ten years, the European catfish (Siluris glanis) has spread further across the basin waters in the Rhineland as species are frequently found in the Braassemermeer, Kagerplassen and the southern part of the Ringvaart.

The European catfish was virtually extinct in the Netherlands until about 25 years ago. Only in the Westeinderplassen and the Ringvaart of the Haarlemmermeerpolder were they occasionally found. Since the turn of the century, however, catfish have been on the rise again in the country, especially in the major rivers and connected waters.

You can help EAA Netherlands by registering your catfish catches here

You can find the full article on this research here

Meervalonderzoek hoogheemraadschap van Rijnland Populatieomvang Westeinderplassen en verspreiding over de boezem. 2022

Photo credits: Sportvisserij Nederland
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