Viability analysis of endangered crayfish populations

The noble crayfish Astacus astacus L. is a threatened freshwater invertebrate. Many of the remaining populations are isolated and there is considerable concern that diseases and the increased frequency of flooding events may drive these remnant populations to extinction. We performed a population viability analysis for a typical isolated noble crayfish population. We quantified the extinction risk by the mean time to extinction within 1000 years for several scenarios (flooding events, restocking of adults). For a set of parameters derived from field estimates, we estimated the mean time to extinction to be 240 years. However, the median was only 80 years. Multiple sensitivity analysis by logistic regression revealed that spawning probability, juvenile and adult mortality were the important parameters for the survival of the population. The mean time to extinction decreased with increasing frequency of floodings. This is alarming, considering the magnitude of the effect and the expectation of an increasing number of floodings with global warming. Restocking, however, was found to have only a minor effect on the mean time to extinction. Overall, our simulations suggested that for the long-term and self-sustaining survival of the noble crayfish, particularly where they remain isolated, we have to improve the extent and quality of habitats. Nevertheless, additional measures are necessary, especially the removal of dispersal barriers to allow some exchange of individuals between populations. However, this also calls for a control of invasive crayfish species.