On the threat to the European crayfish: A contribution with the study of the activity behaviour of four crayfish species (Decapoda: Astacidae)

Abstract

The population size of the native European crayfish species has greatly decreased in the last century due to the crayfish plague and replacement by imported species, the destruction of their habitats, overfishing and eutrophication. In the present paper, the activity behaviours of two European ( Astacus astacus and A. leptodactylus) and two American crayfish species ( Orconectes limosus and Pacifastacus leniusculus) of the family Astacidae are studied and compared. The four crayfish species are not exclusively active during the night. The day-activity of the American crayfish species P. leniusculus and O. limosus with 33% and 22% of their total activity was much higher than those of A. astacus (12%) and A. leptodactylus (16%). All species show a relative high activity at a water temperature of 4°C. From measurements at 25°C and 30°C can be concluded that P. leniusculus and A. leptodactylus are better adapted to high temperatures than A. astacus and O. limosus. At 20°C the covered distance by the four species was calculated from the activity time and running speed. A. leptodactylus covers a distance of about 1600 m per day. In constrast, the distance covered by P. leniusculus is only 200 m. Thirteen biological parameters, including the findings in the activity behaviour, are summarized and discussed as an attempt to describe the causes and mechanisms of species replacement.