Indicators of movement and space use for two co-occurring invasive crayfish species

Red swamp crayfish (Procambarus clarkii) and signal crayfish (Pacifastacus leniusculus) are two invasivefreshwater species with a worldwide distribution. The objective of this work was to investigate how thetwo species move and use space in an area of recent coexistence. Simultaneously, we test the use ofnew tools and indices to describe their movement patterns. To accomplish this we performed a radio-tracking program within a river-type habitat during two different periods (September/October 2010 andJune/July 2013). We used spatial analysis tools to map crayfish radio-location data with and withoutaccounting for the curvature of the river. To assess the consistency of the direction of movement and ofthe distances traveled by crayfish, two indices were developed. To assess the habitat preferences of eachspecies we applied Ivlev’s Electivity Index and the Standardized Forage Ratio. Movement of P. clarkii andP. leniusculus differed. The average detected movement was 8.8 m day−1for P. clarkii and 17.5 m day−1forP. leniusculus. However, crayfish behavior ranged from almost complete immobility – sometimes duringseveral days – to large movements, in half a day, up to a maximum of 255 m for P. clarkii and 461 m forP. leniusculus. The proportion of upstream or downstream movements was independent of the speciesand both species displayed no preference for either direction. The indices of consistency of movementshowed a large interindividual variation. Species and period (2010 or 2013) affected the mean dailydistance traveled, maximum observed distance from location of release and percentage of observationsunder vegetation cover. The Ivlev’s Electivity Index and the Standardized Forage Ratio presented similarresults. P. clarkii showed a preference for pool areas with riparian vegetation cover while P. leniusculuspreferred riffle and pool areas with riparian vegetation cover. Our work provided new and valuable datafor modeling the active dispersal of these two problematic invaders in a context of coexistence.