Abstract

The behaviour and shelter choice of adult noble crayfish (Astacus astacus) and signal crayfish (Pacifastacus leniusculus) were studied in ponds situated at the Evo Game and Fisheries Research Institute, Finland. Three ponds were constructed to reflect typical natural shore morphology, with three layers of artificial shelters for the crayfish at different depths (0 – 35 cm, 36 – 70 cm and 71 – 105 cm). Each pond was divided into two separate compartments, one compartment in each pond was stocked with a predator (pike (Esox lucius) weighing approximately 500 g). Each pond was stocked on 17 May with individually marked crayfish of both species. Seven individuals from each of three groups (males, berried females, and skipping (non-ovigerous) females) were stocked, giving a total of 42 crayfish in each compartment (2 species x 7 individuals x 3 groups). Their behaviour was monitored, and recorded every weekday morning from 25 May to 10 June, with a video camera. The results showed that both noble and signal crayfish occupied shelters at a similar rate with a slight difference in response to the presence of a predator. Noble crayfish seemed to prefer shallower water than signal crayfish, and we also observed a difference in the preferred water depth between skipping females of the two species. No difference was observed between the species among berried females or males in preferred water depth, though mortality of berried females seemed to be higher.

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