Eradication of non-native fish species from some high altitude alpine lakes

The brook trout (Salvelinus fontinalis) is a salmonid originating from North America. This species was introduced in some GPNP lakes in the 1960s when the damage to the ecosystem that could be caused by non-native species was not fully understood.

This is an allochthonous species, in fact, that is to say, a species that colonises an area other than its natural habitat through direct or indirect human action.

Today, scientific knowledge is much more advanced and the International Union for the Conservation of Nature (IUCN) views the introduction of non-indigenous species as the second greatest cause of the drastic loss of biodiversity that is affecting our planet.

If conditions are favourable, in fact, alien species will proliferate fast, altering the delicate balance of the colonised ecosystems.  The impact of the brook trout on the lakes of Gran Paradiso National Park has been studied within the framework of a multiannual research program.

Newly introduced species can harm an ecosystem in may ways: the alien species may compete for the resources available with ecologically similar species, or, in the case of predators, cause the extinction of or dramatic changes to the fauna it feeds on. This is the case of the brook trout: the lakes of the park, in fact, would be devoid of fish in their natural state and the fauna would consist primarily of invertebrates and one amphibian species. The results of the research have shown that the advent of this “super-predator” has disrupted the natural ecosystems, undermining their biodiversity through the disappearance of many species of zooplankton (including rare populations of native Daphnia pulicaria), many aquatic arthropods (Coleoptera, Trichoptera, Hydrochara) and the common brown frog (Rana temporaria). 

Thus, the LIFE+ BIOAQUAE project aims to attenuate the impact of the brook trout on the aquatic ecosystem by eradicating – i.e., removing – this species from some of the Gran Paradiso lakes.

The intervention will be performed starting in early summer 2013, when the waters are free of ice, in three small, shallow lakes, 4 to 10 m in depth – Lake Djouan, Lake Nero of Djouan and Lake Dres –, and in a bigger and deeper lake, Lake Nero of Leynir (22 m). Due to the appreciable depth of this lake, the intervention will have a markedly experimental and innovative character. The eradication process will be carried out by means of fishing nets and electrofishing. 

The fish caught in this manner will be stored in fish cages submerged in the lake, moved down the valleys for veterinary checks and, as much as feasible, distributed to public refection structures.

The eradication methods therefore will be non-invasive, ruling out the use of chemical products and using only mechanical and manual means, in order to minimise the impact on the native species and the ecosystems to be safeguarded.

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