Habitat restoration as a management tool for invasive American bullfrog

The control of invasive alien species is essential for securing native biodiversity. As for the American bullfrog, Lithobates catesbeianus, suspected to cause ecological damage to native amphibians around the globe, comprehensive management techniques are currently absent. We investigated two contrasting approaches to control the species in permanent, small and shallow water bodies in Flanders (northern Belgium). Small and isolated populations were actively managed through trapping with double fyke nets. The catchability of tadpoles averaged 6 % of the population with the specified sampling gear, implying feasible perspectives for a full eradication of the species when maintained over multiple years in the infested water bodies. In large and interconnected metapopulations, where active control is no option, we explored possibilities of passive management through habitat restoration. Using an experimental setup, we investigated the effect of complete drawdown with amphibian and fish removal versus predation by introduction of native northern pike, Esox Lucius, on bullfrogs. The presence of pike lead to a strong decline in tadpoles, while no effect of drawdown was present. Also, communities receiving pike harboured substantially less small and mostly planktivorous fish species (e.g. pumpkinseed, Lepomis gibbosus, and topmouth gudgeon, Pseudorasbora parva). Under these conditions of permanent, small and shallow water bodies, biomanipulation using a native predatory fish species can effectively lead to a change in food web interactions to the detriment of bullfrog. This method may thus be regarded as a candidate for effective and sustainable control of invasive bullfrog populations.