Activity patterns, behavioural repertoires, and agonistic interactions of crayfish: A non-manipulative field study

Agonistic behaviour of crayfish has been studied extensively in laboratory settings where pairs or groups of individuals are allowed to interact within an experimental arena. Crayfish agonistic behaviour within its natural context, however, has received little attention to date. The present, non-manipulative field study explored activity patterns, behavioural repertoires, and agonistic encounters of rusty crayfish (Orconectes rusticus) during the summer months using continuous, 24-hour, underwater video recording at a series of representative field sites. Following the filming, crayfish within the vicinity of the camera site were captured and measured. Individual densities were high, reaching a maximum of 68 individuals/m(2) at some sites. Large crayfish predominantly inhabited deeper sections of the river and were mostly active at night, whereas small crayfish generally utilized the shallows and were active outside their bur-rows during day and dusk. Time outside their shelter was mainly used for feeding. Individuals frequently returned to the same shelter they had emerged from. Agonistic encounters were common events and generally occurred in the context of shelter acquisition or defense. Dyadic fighting progressed with escalating sequences of stereotyped aggressive acts. Furthermore, high intensities with unrestrained use of claws were seen in encounters between size-matched opponents. The results of this study allow us to root laboratory findings of crayfish aggression within a comprehensive, ethological framework and to consider ultimate consequences for individual fighting decisions and strategies.