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Charting the rise of the wels catfish

Charting the rise of the wels catfish

Fifteen years ago, the rise of the wels catfish in the Netherlands prompted Sportvisserij Nederland (Dutch angling association) to set up an online ‘Wels catfish hotline’ in order to map the spread of this significant sport fish. Catches have recently been registered by means of this hotline, enabling even better mapping of the distribution of this mysterious fish.

The first report on the wels catfish in the Netherlands – released in 2011 and based on data from the hotline, MWTL (a programme monitoring the state of the nation’s waters) and RAVON (a conservation organisation for native reptiles, amphibians and fish) – revealed that, at the time, the spread of this catfish was concentrated around the large rivers, the Oude IJssel, the area around Haarlemmermeer and the Flevopolders. The largest concentrations of wels catfish were found in the tidal rivers near Rotterdam and in the Limburg Maas.

Continued proliferation 

The number of wels catfish caught by anglers increased, and the species began appearing more frequently in other areas, prompting Sportvisserij Nederland to update the old 2011 report. The latest survey was based on data gathered from the upgraded wels catfish hotline, MijnVISmaat (the Sportvisserij Nederland catch registration system) and Piscaria (the national fish database). The results overwhelmingly confirmed the spread of the wels catfish: in 2011 they were recorded in 160 ‘uurhokken’ (5 km grid squares used to assess biodiversity), but have since spread out to be recorded in 231 grid squares on the new distribution map.

It is interesting to note that the species is increasingly being found in smaller waters – often in the form of very large specimens – and that they are most concentrated in the area around Rotterdam. The conclusion is clear: the wels catfish is continuing to spread across the country, and there’s a good chance of records being broken again this year.

The distribution of wels catfish caught in the Netherlands, displayed in a heat map (Legend: high density and low density).

Wels catfish hotline

The new heat map shows that the occurrence of wels catfish has increased mainly around Rotterdam and the major rivers. The northern provinces are still lagging behind, however. A similar survey was carried out in 2011, when the wels catfish was just beginning to appear in the Netherlands. At the time, the spread of this fish was inventoried by means of a wels catfish hotline, with the following map being the result:

Report your catches!

The wels catfish (Siluris glanis) is on the rise in the Netherlands. Both major rivers and smaller water channels like navigation and drainage canals often have their own wels catfish populations. Sportvisserij Nederland (Dutch angling association) conducts research to monitor the spread of this species. The results are then compared to those of a similar study conducted 10 years ago to identify how the fish is spreading.

Anglers who catch one or more wels catfish in the Netherlands are therefore encouraged to report their catches (locations will not be made public). When you report a catch, you also have a chance to win one of several wels catfish-related prizes. So go to the Meervalmeldpunt (Wels catfish hotline) to report your wels catfish catch today.

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