Autumn has come, and with it the first season of fieldwork for the eradication of brook trout (Salvelinus fontinalis) from the alpine lakes of the Gran Paradiso National Park has come to an end. The eradication of this non-native trout is one of the initiatives undertaken under a three-pronged plan, the LIFE+ BIOAQUAE project. Based on the satisfactory results obtained so far, prospects look good for the recovery of these high elevation aquatic ecosystems.
In order to eradicate this introduced species originating from North America, an aggressive predator whose presence has greatly undermined the biodiversity of the alpine lakes, LIFE+ BIOAQUAE researchers placed tens of fishing nets in each of the 4 lakes included in the eradication program. Fishing activities went on continuously for over three months (from June through September), resulting in the removal of ca 8000 fish and a sharp drop in fish population density in the lakes.
The chart on the right shows the typical catch rate for brook trout as recorded in the Djouan Lake in Valsavarenche: the high number of fish caught during the first few days declined fast and the rate stabilised over values close to zero as the fieldwork season progressed.
The results obtained indicate that the eradication methods employed (fishing nets and electrofishing) work well for this type of intervention, which will be carried on in the coming years. The good news is that a few timid but significant signs of ecosystem recovery may already be discerned. Dozens of dragonflies are flying over the Dres Lake in Orca Valley and Daphnias are swimming in the pelagic zone; for the first time, some Dytiscidae(tiny swimming Coleoptera) have been seen in the Nero Lake in Valsavarenche, while in the Djouan Lake, in the same valley, frogs are back in great numbers and quite a few caddisflies are managing to survive.
The five-year project is still in its early stage, but the return of some of the autochthonousspecies to the alpine lakes is a positive sign that engenders enthusiasm and confirms the importance of this action. During the long alpine winter, while the fishing nets continue their slow work of capturing the fish beneath the frozen surfaces of the lakes, the researchers will conduct laboratory analyses on the samples collected. In the spring of 2014, a new eradication drive will get underway, and it is hoped will provide further evidence of the efficacy of this action.
Eradication: removal of a species from a location, in this case, removal of brook trout from the alpine lakes.
Introduced species: a species non-native to a site, which has been transported to the new location either directly or indirectly by human activity; also referred to as allochthonous species.