In the past few centuries, the natural habitats of the crayfish have been destroyed piece by piece by human impact. Many water bodies lack natural structures that the creatures can use as shelter. In addition, the crayfish suffer from the pollution of the waters with pesticides and heavy metals. The situation worsened dramatically when North American crayfish species were introduced to Europe from the 19th century onwards to compensate for the decline of native crayfish. The invasive crayfish not only proved to be much more competitive than the native ones and contested their habitats, but they also brought the crayfish plague to Europe.
While the alien crayfish themselves were already very resistant to this infectious disease, which also originated in America, there was a dramatic decline in native crayfish. Even today, outbreaks occur again and again, in which very many creatures die.
What is the current situation?
Today, the large waters of Switzerland are full of alien crayfish, which belong to a total of four species: eastern crayfish, signal crayfish, red American swamp crayfish and Galician crayfish. The native crayfish have been almost completely pushed back into remnant populations in headwaters that are largely isolated from each other.
In order to protect stone crayfish, white-clawed crayfish and noble crayfish, the Swiss Federation launched the "Swiss Crayfish Action Plan" in 2011, which has since been implemented by the cantons. After ten years, the objective – to conserve the stocks and, if possible, to increase them again – is more relevant than ever.