Identification of alien predators that should not be removed for controlling invasive crayfish threatening endangered odonates

1. When multiple invasive species coexist in the same ecosystem and their diets change as they grow, determining whether to eradicate any particular invader is difficult because of complex predator-prey interactions. 2. A stable isotope food-web analysis was conducted to explore an appropriate management strategy for three potential alien predators (snakehead Channa argus, bullfrog Rana catesbeiana, red-eared slider turtle Trachemys scripta elegans) of invasive crayfish Procambarus clarkii that had severely reduced the densities of endangered odonates in a pond in Japan. 3. The stable isotope analysis demonstrated that medium-and small-sized snakeheads primarily depended on crayfish and stone moroko Pseudorasbora parva. Both adult and juvenile bullfrogs depended on terrestrial arthropods, and juveniles exhibited a moderate dependence on crayfish. The turtle showed little dependence on crayfish. 4. These results suggest that eradication of snakeheads risks the possibility of mesopredator release, while such risk appears to be low in other alien predators. Copyright (C) 2011 John Wiley & Sons, Ltd.