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, Sp ain), has been studied using both traditional and radio-telemetry technique s. Our results lead us to propose that P. clarkii shows two opposed pattern s of activity, featuring (1) a wandering phase, without any daily periodici ty, characterised by short peaks of high speed of locomotion, and (2) a lon ger stationary phase, during which crayfish hide in the burrows by day, eme rging 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 po int of release within four days. This intensive activity helps dispersion i n this species. Further studies are required to understand the adaptive sig nificance of this locomotory behaviour, which appears expensive and dangero us, and the mechanisms of home-range recognition and orientation.