An isolated population of the white-clawed crayfish (Austropotamobius pallipes) in the principality of Liechtenstein

摘要

An isolated stock of Austropotamobius pallipes is studied in a small water systemdraining into a tributary to the river Alpenrhein in the Principality of Liechtenstein. Thepopulation is known to originate from one single stocking activity of 109 specimens in1985. Crayfish stock is investigated by direct observation at night and by trap catchingincluding mark and recapture. Essential ecomorphological properties of the waters arerecorded in respect to their attraction for crayfish. The stock is spread over two smallnatural ground water ponds and some connected ditches. The settled area is only 850metres in total longitudinal extension and the boundaries of the stock are very sharp overonly few metres on all sides following distinct changes of morphometry, structure or waterflow which prevent the population from expanding. In addition, isolation from thedownstream fauna is given by a local source of water pollution. The distribution ofpopulation density shows a heterogeneous micro-scale pattern corresponding to thedistribution of structures and substrates in the waters. The population was estimated to atleast 2.000 individuals. No subsidiary stocks were found in the ditch system. Parasiticgrowth of Branchiobdella pentodonta is very high and affects all individuals. Fish stock isconfined to the species bullhead Cottus gobio , minnow Phoxinus phoxinus and brown troutSalmo trutta f. fario in low densities. Fish prédation has no impact on the crayfishpopulation. The waters are situated in a natural reserve, neither fish nor crayfish stocksare exploited by man. Stock situation and management are discussed.