Movement patterns and ranging behavior of the invasive spiny-cheek crayfish in a small reservoir tributary

Nineteen adult O. limosus (carapace length 26.3-35.7 mm) were radio-tagged and tracked in a small tributary to a reservoir during two time periods, from May to June and from October to November 2007. High nocturnal activity (33.3 %) and relatively high diurnal activity (18.2 %) were observed, with a positive effect of cloudy weather on nocturnal movements. Tracked crayfish showed a high ability for rapid upstream (62 m) and downstream (69 m) movements during short (3 h) time periods. The average movement distances per day were one order of magnitude lower (7.2 and 6.7 m in spring, autumn, respectively). The maximum daily movement was 139 m. A significant trend to downstream migration to the reservoir was observed in autumn. Fifteen specimens displayed homing behavior, with the use of a system of shelters. A preference for soft bottomed, deeper areas of the brook. and for slow flow areas, such as pools, with the presence of organic matter was observed. Fluctuations in crayfish density, together with downstream migration in autumn, suggested that crayfish inhabit the brook only during the growing season, over-wintering in the reservoir. This study provides information on the spatial and temporal behavior of invasive species in small tributaries suitable for indigenous crayfish and illustrates their serious threat for it.