Crayfish

More and more American crayfish live in the Netherlands. In our management area there are three species: the spotted, knobbed and red American crayfish. The American crayfish is an invasive exotic species. This means that it does not occur naturally in the Netherlands but can live well here. The crayfish reproduce quickly. They also have almost no natural enemies in our waters. As a result, their numbers are increasing rapidly. 

Damage 

Red American crayfish dig burrows and tunnels in water bottoms and banks. Sometimes they also dig a section in a levee. Their digging can cause banks to crumble or sink. Crayfish also eat water plants or cut them up. Then silt from the bottom gets into the water, reducing sunlight and giving algae a better chance to develop. It is then harder for other and new aquatic plants to grow. This is ultimately to the detriment of biodiversity. 

What does HHNK do?

The emergence of American crayfish is a nationwide problem. Many water managers are dealing with it and several studies are being done to find a successful approach. However, one has not yet been found. Crayfish are increasingly being eaten by native species such as blue heron, grebe, perch and pike, but that doesn't seem to be helping enough to reduce numbers.

Besides crayfish, several (invasive) exotics occur within the management area of HHNK. In recent years we have experienced an increase of these. See the page Invasive exotics.

Catch

Crayfish can't just be caught. Currently (2021), only professional fishermen with special permission may catch the non-native species with traps or crayfish pots and sell them. Sport fishermen may only fish for crayfish with a rod. Only if the angling club has full fishing rights may they also be taken. Use a properly sealable bucket for this purpose so that the animals are not inadvertently dispersed. It is forbidden to release the crayfish in other waters than where they were caught. Crayfish lay hundreds of eggs at a time, so moving one crayfish can already create a new population. 

Report

If you have seen crayfish somewhere, you can report it via the app 'SnApp de exoot' or the websie Waarneming.nl. Please include a clear picture so we can see which species it is.

Learn more

Are you curious which species you have seen? Take a look at the search chart of Stichting EIS or the more extensive species finder of Naturalis, for example. 

More information on crayfish can be found on the websites of the Crayfish Knowledge Platform, EIS Foundation, STOWA (Stichting Toegepast Onderzoek Waterbeheer) or the Province of North Holland.