Eradication of introduced brook trout and recovery of alpine lakes in the Gran Paradiso National Park (Italy)

Alien fish have been introduced into once fishless mountain lakes worldwide, seriously affecting biota. In the Gran Paradiso National Park (GPNP, Western Italian Alps), the impact of introduced brook trouts fish (Salvelinus fontinalis) on biodiversity in high altitude alpine lakes was quantified, and was so strong as to lead the GPNP to undertake an eradication campaign, financed within the EU financed LIFE+ BIOAQUAE (Biodiversity Improvement of Aquatic Alpine Ecosystems) project. The eradication started in June 2013 in Starting in June 2013, BIOAQUAE provides for the eradication of S. fontinalis from three small lakes (depth range: 3-7.4 m) and one large lake (depth: 22.1 m), experimental lake. Intensive gill netting and electrofishing have been were used as a non-invasive eradication techniques, without lethal effects for native species, potentially including unique taxa, evolved thanks to the island-like nature of alpine lakes (e.g. rare alpine haplotypes of Daphnia pulicaria). The effects of the eradication are The ecosystem resilience is being monitored, along with the eradication campaign, using a BACI design, comparing the lakes subject of the eradication project with in the treated lakes and the data from a set of control lakes (both naturally fishless lakes and orlakes still containing brook trouts) as a reference to quantify the ecosystem resilience using several indicators (hydrochemistry, water transparency, zooplankton and macroinvertebrate communities, emergent insects, and amphibians populations). At the end of its its second seasonyear, the eradication action within the LIFE+ BIOAQUAE project was successful in eradicating S. fontinalis from two small lakes, the fish population is collapsing in the other two other lakes, and there are strong evidence of ecological resilience, with macroinvertebrates being particularly sensitive to fish removal. To the best of our knowledge, this is the first time that such an eradication programme is succesfully implemented in high altitude lakes in the European Alps.