Predator avoidance and vulnerability of two co-occurring crayfish species, Astacus astacus (L.) and Pacifastacus leniusculus (Dana)

Abstract

Juveniles of the native crayfish Astacus astacus and the newly introduced crayfish Pacifastacus leniusculus were reared separately in artificial ponds in the presence and absence of a predatory fish, the European perch (Perca fluviatilis), to measure the ef fects of this predator on the behaviour and survival of the two species. The two species responded strongly and similarly to the presence of perch by changing microhabitat use, thereby reducing their exposure to the predator. Crayfish that were observed outside of shelter did not tend to stay closer to shelter in the presence of perch than in perchless controls. The presence of perch increased the mortality of both species, but there was no significant difference in predation vulnerability between the two species. The prediction that A. astacus, because of a common evolutionary history with perch, should show stronger and more effective antipredator responses and therefore suffer a lower mortality rate than P. leniusculus was not supported. The juvenile growth rate is slower in A. astacus than in P. leniusculus and, consequently, A. astacus is at a preda tion-vulnerable size for longer. The total risk of mortality due to predation during the whole juvenile period may therefore be higher for A. astacus than for P. leniusculus.