The Combined Effects of Multiple Invasive Species on Persistence of Imperiled Pahrump Poolfish

Many ecosystems have been invaded by more than one non-native species, but research evaluating the combined effects of multiple invasive species has been limited. In the southwest USA, many aquatic systems have been invaded by multiple species such as non-native crayfish and non-native fishes. We document the rapid decline of a population of the endangered Pahrump Poolfish, Empetrichthys latos, which occurred following the sequential introduction of Red Swamp Crayfish, Procambarus clarkii, and Western Mosquitofish, Gambusia affinis. We also report the results of mesocosm experiment where we tested individual and combined effects of invasive Red Swamp Crayfish and Western Mosquitofish on experimental populations of Pahrump Poolfish. Survival rates were near 100% for adult poolfish in allopatry but were significantly lower for the other two treatments; when poolfish were sympatric with crayfish (~53%), and when poolfish were sympatric with both crayfish and mosquitofish (~55%). In allopatry, poolfish produced over 90 juveniles per mesocosm, while approximately 65 juveniles per mesocosm when poolfish were sympatric with crayfish, but this difference was not significant. However, juvenile production plummeted to near zero when poolfish were sympatric with both crayfish and mosquitofish. This study demonstrates that Pahrump Poolfish must be actively managed to detect and control invasive species, otherwise extinction will likely occur. This study also provides an example of the compounding effects of multiple invasive species.