The dispersion of the Aphanomyces astaci-carrier Pacifastacus leniusculus by humans represents the main cause of disappearance of the indigenous crayfish Austropotamobius pallipes in Navarra

The tendency of population decline of the indigenous crayfish, Austropotamobius pallipes, in Navarra was reduced by the implementation of a plan of restoration in 1996. Recently, a new drop in population numbers has been noticed. In 2004, an extensive survey was carried out to study the reasons for this decline. The results showed that indigenous crayfish had disappeared from 37 out of 73 areas where they were previously present. The main causes were found to be: presence of signal crayfish, Pacifastacus leniusculus (40%), habitat alterations (13%) and climatic drought (11%). In 35% of the cases, the reasons could no be determined. Disappearances that were associated with presence of signal crayfish were assigned to crayfish plague. These disappearances have occurred a few years after an increase in the number signal crayfish fishery areas. The new populations of P leniusculus followed a patchy distribution, and were clearly associated with human introductions. This work shows that signal crayfish currently represents the main reason for decline of indigenous crayfish and that humans play a major role in the dispersal of these carriers of the causative organism of crayfish plague, A. astaci.