Five brigades coordinated by the biologist Marc Ventura, from the Center for Advanced Studies in Blanes (CEAB-CSIC), continue this summer the mission of eliminating trout and verons from ten high mountain lakes, in the national park of Aigüestortes and Estany de Sant Maurici and in the natural park of the High Pyrenees. “All the fish in the ponds are invasive, as they have not arrived there naturally, most of them were introduced by fishermen in the middle of the 20th century indiscriminately, which created conservation problems; the aim is to restore the original state of these lake spaces and promote the recovery of threatened amphibian populations, such as the Pyrenean newt, the red frog and the midwife toad”, underlines Ventura.
The initiative is part of the European Life Resque Alpyr project, which takes over the LimnoPyreneus, and which is also carried out in the Italian Alps. In fact, in the previous program, which was developed during the period 2014-2019, it was possible to completely eradicate the veron from the Closell and Rovinets ponds, for the first time in the world using traditional techniques (traps, electrofishing and nets). The trout were also eliminated in Cap de Port, Cabana and Subenuix, and the two species in the two small ponds in Dellui, Ventura points out.
Now, efforts are concentrated on the lakes of Naorte, Montanyó and two of the Tres Estanys enclave, in the Alt Pirineu park, and those of Llastra, la Coveta, Gargoles Inferior, Cabidornats, Dellui and Manhèra, Aigüestortes and Estany de Sant Maurici or in its peripheral area.
Ventura details that the action focuses on three species of trout (common, brook and rainbow trout) and three of verón, a small fish that is barely ten or twelve centimeters long, but which has a harmful impact. This cyprinid eats the larvae of insects and crustaceans that feed on algae. Without crustaceans, marine plants proliferate, the water turns green and visibility is reduced.
Ventura highlights the challenge of creating a series of trout-free sectors and Veronsal parks, so that the Pyrenean newt can go from one lake to another without danger of being eaten. “This newt is endemic to the Pyrenees, and in Aigüestortes there is a unique genetic lineage that is threatened by the exaggerated presence of fish”, adds the researcher.
If in Catalonia there is an awareness of the need to completely neutralize the presence of trout and verons, in France it is more difficult to convince of the urgency to implement programs aimed at restoring the health of the lakes by suppressing salmonids. “In France there is not a single pond without fish, while, for example, in Aigüestortes, which is where there are more fish in Catalonia, 30% have none,” says Ventura. “We are now collaborating with the French to explain the situation to them, they said we were crazy, they didn’t understand, now they are starting to act with a pilot test in La Cerdanya”, he adds.
It should be noted that fishing is prohibited within the national park, although it is permitted in the peripheral area of ??this protected area.
The Generalitat has been involved in this project by financing an action to also eradicate the trout from the Collada lake, and soon plans to do the same for those in Travessani, all in the national park.
The capture systems used are nets, lobsters and electric shocks that put them to sleep and facilitate their removal one by one. Likewise, the CEAB-CSIC team is finalizing a pilot test to use a piscicide, a biodegradable chemical substance already tested in other countries that inhibits the gill breathing of animals, as Ventura explains.
Calculations made on the ground indicate that in a medium-sized pond there can be between 500 and 1,500 common or rainbow trout and up to 5,000 brook, and the number of lake trout can be between 100,000 and 200,000. In France, they use this last species as bait and the leftovers are thrown into the lakes.
The tasks will culminate in 2026 to fulfill the objective of restoring the species composition and ecological function of the high mountain lakes of the Pyrenees, and also of the Italian Alps, with the eradication of fish.
