Rapid amphibian community recovery following removal of non-native fish from high mountain lakes

Amphibians of high mountain lakes face many threats related to global change, including novel pathogens, development, climate change and overexploitation. However, the foremost threat is the presence of non-native fish. One of the objectives of the LIFE+ LIMNOPIRINEUS project (2014–2019) was the recovery of protected amphibian communities (including the endemic Calotriton asper) in eight naturally fishless Pyrenean high mountain lakes, by controlling or eradicating non-native trout or minnows. During the summer months of 2015 to 2019, we removed 95–100% of the fish present in these lakes, and monitored changes in their amphibian populations, as well as surveyed 56 nearby control lakes with or without fish. We found rapid natural recovery of amphibian communities as fish removal work progressed. The fish-removal lakes achieved typical richness figures for the area one year after fish removal began, and typical species abundances after three years (with the only exception of Rana temporaria). We documented a total of 16 colonisation events, all by amphibian species from the same valley. The two earliest colonisation events were observed in the year in which fish removal began, with eight events the following year. The lack of colonisation from nearby valleys in the study period highlights the crucial role of nearby residual populations not affected by human impacts. We show that whole amphibian communities from high mountain lakes recover rapidly after eliminating or reducing non-native fish, proving that this is a powerful tool to improve the conservation status of endangered amphibians.