River crayfish: trends in numbers
The river crayfish, once common, is now found in only one brook in the Netherlands.
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Trends
The European river crayfish used to be so numerous in brooks and rivers that it was caught and eaten. Prior to 1920 there were still 44 water bodies where it occurred, but around 1975 the number had declined to ten.
The species is currently found in only one brook in the Netherlands: the Rozendaalse Beek on the Veluwe. Here too it is greatly endangered. In 2001 it was found that 2 of the 3 remaining locations in the brook in which the species occurred had disappeared. It is thought that crayfish plague is responsible for the species' mortality. Elsewhere in Europe the species has become very rare; it is one of the endangered species in Europe.
The reasons for the decline are worsening water quality, and the straightening and regulating of brooks and rivers. At the end of the 19th century crayfish plague, a fungal disease, also struck. The disease arrived via exotic crayfish that have since established in freshwater habitats in the Netherlands: the Turkish crayfish, the American red swamp crayfish and the American spiny-cheek crayfish. These three species have been able to supplant the native river crayfish in a number of water bodies because they are more tolerant of water pollution and are resistant to crayfish plague.
The river crayfish is in Annex V of the Habitats Directive.
