Sex- and size-specific migration patterns and habitat preferences of invasive signal crayfish (Pacifastacus leniusculus Dana)

In freshwater ecosystems, the invasion of alien crayfishes is considered a major threat to native populations. In particular, signal crayfish (Pacifastacus leniusculus) are increasingly replacing native stone and noble crayfish populations in Europe. In this study, population characteristics, habitat preference, as well as sex- and size-specific migration patterns of signal crayfish were analyzed within a model study section in the river Moosach (Danube drainage), Germany. A total of 1162 crayfish at a minimum population density of 0.4 specimens per m2 and a sex ratio of 1.18 males to 1 female were found. Habitat preference was size-specific, with smaller specimens preferring shallow, gravel-dominated sites, and large animals preferring deep, saprobel-dominated sites. Migration behavior was strongly influenced by the sex and size of the crayfish, with large males showing the greatest migration distances of up to 300 m within 7 days. The correlation between the migration distance and the time period between capture and recapture was generally low but strongest for small female crayfish. The results of this study suggest that local population characteristics, particularly the density, size-distribution and sex ratios, can strongly influence the dispersal ability of invasive crayfish.