Abstract

The effects of water level regulation and the presence of a predator on the mortality of juvenile noble crayfish, Astacus astacus, were investigated in two different experiments in ponds at Evo research station (Finland). The juvenile noble crayfish were provided with hides in the ponds and perch (Perca fluviatilis) (10 – 20 cm TL) were used as predators. Hides in the form of small gravel piles, perforated bricks or flat rocks were provided either along the shoreline or extending to depths of 50 cm at maximum water height. Two different water level regulation patterns were tested: water level lowering during the day or at night with a steady water level being used as a control. Perch preyed on juvenile noble crayfish under all circumstances tested. The observed differences among treatments were small and mostly pointed to trends rather than representing significant differences. The main observations were, that survival was higher when the hides extended from the shoreline into deeper water, whereas, lowering of the water level at night increased juvenile noble crayfish mortality.

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