Use of a native predator for the control of an invasive amphibian

Context The control of invasive alien species is essential for securing native biodiversity. As for the American bullfrog, Lithobates catesbeianus (Shaw 1802), suspected to cause ecological damage around large parts of the globe, comprehensive management techniques are currently absent. Aims To fill this gap, opportunities arising from biomanipulation of permanent water bodies inhabited by fish were explored. Methods A multi-annual experiment was performed in small and shallow ponds, and effects of complete drawdown (with amphibian and fish removal) and predation (introduction of originally occurring native northern pike, Esox lucius) on non-indigenous bullfrogs were investigated. Key results The presence of pike lead to a strong decline in bullfrog tadpole numbers, whereas no effect of drawdown was observed. Also, communities receiving pike harboured substantially less small and mostly planktivorous fish species (e.g. pumpkinseed, Lepomis gibbosus, and topmouth gudgeon, Pseudorasbora parva). Conclusions The reduction in bullfrog tadpoles may be assigned to both direct and indirect effects induced by pike. First, direct pike predation on tadpoles was observed. Second, as the occurrence of macroinvertebrate-feeding pumpkinseed was low in the presence of pike, the indirect effect of predation by macroinvertebrates on tadpoles may significantly increase, leading to tadpole decline. Implications Biomanipulation of permanent water bodies inhabited by fish can thus be regarded as a candidate for effective and sustainable control of invasive bullfrog. Piscivorous fish introduction may be applied in the specific type of water body, but requires careful consideration of the indigenous status of the introduced species, angling purposes, or specific nature values.