Invasive crayfish: activity patterns of Procambarus clarkii in the rice fields of the Lower Guadalquivir (Spain).

The activity of a naturalised population, of the invasive Nearctic crayfish, Procambarus clarkii, in the Lower Guadalquivir rice fields (Andalucia, Spain), has been studied using both traditional and radio-telemetry techniques. Our results lead us to propose that P. clarkii shows two opposed patterns of activity, featuring (1) a wandering phase, without any daily periodicity, characterised by short peaks of high speed of locomotion, and (2) a longer stationary phase, during which crayfish hide in the burrows by day, emerging only at dusk to forage. Other behaviours (such as fighting or mating) also take place at night-time. During the wandering phase, breeding males move up to 17 km in 4 days and cover a wide area (up to 20 km(2) in 4 days). Breeding males fitted with radio-transmitters were tracked back to the point of release within four days. This intensive activity helps dispersion in this species. Further studies are required to understand the adaptive significance of this locomotory behaviour, which appears expensive and dangerous, and the mechanisms of home-range recognition and orientation.