Abstract

The crayfish Astacus astacus is widely spread in waters of the region of Oberfranken (North-Eastern Bavaria) but occurs in rather isolated populations. It prefers brooks or small rivers with soft ground. In the waters of the region A. astacus is potentially endangered. In cooperation between the District Fishery Association Oberfranken and the Fishery Department (Fishery Advisory Service) we have started a programme in 1984 to rescue and to enhance the last crayfish populations in the region by stocking juveniles (3-4 cm) in brooks and small rivers every year in September or October, in order to establish stable populations. Meanwhile this programme is carried out since 14 years. Stable populations have been built up in several brooks, small rivers and natural ponds. The water quality in the Oberfranken crayfish biotopes is grade II to grade III, the pH of the waters ranges from 6.4 to 9.2. The water temperature during the summer period is 14-22°C. An important factor which influences crayfish populations is the fish fauna in the crayfish biotopes. High densities of eel (Anguilla anguilla), catfish (Silurus glanis), perch (Perca fluviatilis) or burbot (Lota lota) are negative for crayfish populations. Also large populations of trout (Salmo trutta fario, Oncorhynchus mykiss) and chub (Leuciscus cephalus) are able to keep crayfish populations at lower densities.

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