Acoustic Signals and Behavior of the Invasive Freshwater Crayfish Cherax destructor (Clark, 1936)

The study of acoustic signals in aquatic animals contributes to developing new monitoring systems based on passive acoustics and improves our knowledge of their behaviors and ecology. Here, the sounds produced by the invasive species crayfish Cherax destructor and their possible role in intraspecific interactions are analyzed. Synchronized acoustic and video monitoring systems were used in a tank to record acoustic signals and associated behavioral events (tail flips, number of encounters, number of fights) and states (velocity and distance moved, angular velocity, duration of fighting and proximity). The crayfish were monitored in seven layouts combining males (M) and females (F) (F, M, FF, MM, MF, MMF, FFM). Both males and females produced two types of acoustic signals (high- and low-frequency sounds). Grouped animals produced fewer low-frequency sounds than single animals. In a grouped layout, more sounds were recorded when animals were in proximity (distance between two specimen less than 6 cm). In a single layout, sounds were not associated with a specific event or behavioral state. The number of signals emitted in the FF group and single M group were significantly higher than those in other layouts. Our study indicates that low-frequency sounds are produced non-accidentally and provide a baseline for future tests on intraspecific acoustic communication on this species. This study could help implement low-cost passive acoustic monitoring able to identify this species and the possible negative effect of its dispersion in a non-native environment.