Crayfish

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

Damage 

Red swamp crayfish dig burrows and tunnels in waterbeds and banks. Sometimes they also dig into dikes. Their digging can cause banks to crumble or collapse. The crayfish also eat aquatic plants or cut them up. This causes silt from the bottom to enter the water, reducing the amount of sunlight reaching the water and increasing the chance for algae to develop. This makes it more difficult for other and new aquatic plants to grow. Ultimately, this is detrimental to biodiversity. 

What does HHNK do?

The rise in the number of American crayfish is a nationwide problem. Many water managers are working on this issue and various studies are being conducted to find a successful approach. However, this has not yet been found. Crayfish are increasingly being eaten by native species such as blue herons, grebes, perch, and zander, but this does not seem to be enough to reduce their numbers.

In addition to crayfish, several (invasive) exotic species occur within the HHNK management area. We have seen an increase in these species in recent years. See the page on invasive exotic species.

Catching

You cannot simply catch crayfish. Currently (2021), only professional fishermen with special authorisation are allowed to catch and sell exotic authorisation using traps or crayfish pots. Recreational fishermen are only allowed to fish for crayfish with a rod and line. Only if the fishing club has full fishing rights are they allowed to take them with them. Use a bucket that can be securely closed so that the animals are not accidentally spread. It is prohibited to release crayfish into water other than where they were caught. Crayfish lay hundreds of eggs at a time, so moving a single crayfish can create a new population. 

Report

If you have seen crayfish anywhere, you can report this via the 'SnApp de exoot' app or the Waarneming.nl website . Please include a clear photo so that we can see what species it is.

More information

Are you curious about what species you have seen? Take a look at the search card from Stichting EIS or the more comprehensive species finder from Naturalis. 

More information about crayfish can be found on the websites of the Crayfish Knowledge Platform, the EIS Foundation, STOWA (Foundation for Applied Water Management Research), or the Province of North Holland.