The success of crayfish stocking in a dredged river with and without artificial shelter increase

Abstract The success of crayfish ( Astacus astacus L.) stocking in a heavily dredged river in Finland was compared between sections with and without artificial shelter. The materials used for creating shelter were a) broken rock and, b) ceramic drain pipes and perforated bricks. Group-marked crayfish (mean carapace length 42.6 mm) were released into the sections and test trappings conducted one year later. The highest crayfish densities were found in the broken rock sections. The reasons for the observed crayfish densities are discussed. No significant differences in growth between groups were detected. Migrations in the range of 2.5 km in one year were recorded.