Campaign to eliminate trout and palms from ten lakes in the Pyrenees

Five brigades coordinated by biologist Marc Ventura, of the Center for Advanced Studies in Blanes (CEAB-CSIC), this summer continued to work to eliminate trout and minnows from ten high mountain lakes, in the Aigüestortes i Estany de Sant Maurici National Park and in the Alt Pirineu Natural Park. “All the fish in the ponds are invaders because they did not arrive naturally, and most were introduced by fishermen in the mid-20th century indiscriminately, causing conservation problems; the aim is to restore the pristine state of these lake spaces and enhance the protection of endangered amphibian populations, such as the amphibian newt, grass frog, and midwife toad,” Ventura asserts.

This initiative is part of the European Life Rescue Alpyr project, which is taking over from LimnoPirineus, and which is also being implemented in the Italian Alps. In fact, in the previous program, implemented in the period 2014-2019, it was possible to completely eliminate, for the first time in the world using traditional techniques (shrimp, electric fishing and nets), minnow from Closell and Rovinets ponds. Trout have also been wiped out in those at Cap de Port, Cabana and Subenuix, and both species in the two smaller ones at Dellui, Ventura said.

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Now, efforts are concentrated on Lakes Naorte and Montanyó and two of the Tres Estanys, in the Alto Pirineu park, in those in Llastra, la Coveta, Gargoles Inferior, Cabidornats, Dellui and Manhèra, in Aigüestortes and Estany de Sant Maurici or in the surrounding area.

Ventura explains that the action focuses on three species of trout (common, char and rainbow) and three trout, which are fish that measure no more than ten or twelve centimeters but leave a sting. This carp devours insect larvae and crustaceans that feed on algae. Without crustaceans, aquatic plants thrive, the water turns green and visibility decreases.

Ventura highlights the challenge of promoting a series of strips in parks that are free of trout and fish so that Pyrenean newt can move from one lake to another without the risk of being eaten. “This newt is endemic to the Pyrenees, and in the Aigüestortes there is a unique genetic lineage that is threatened by the excessive presence of fish,” adds the researcher.

In France, they were reluctant to make a move, and now they’re starting a test run at La Cerdagna

If in Catalonia there is an awareness of the need to completely eliminate the presence of trout and minnow, in France it is difficult to convince of the urgency of implementing programs aimed at restoring the health of lakes by suppressing salmon. “In France, there is no pond without fish, while, for example, in Eguistortes, where there are more Catalonia, there is no pond in 30%,” says Ventura. And he adds, “We are now cooperating with the French to explain the situation to them. They said we were crazy, and they did not understand the matter, and now they have started working with an experimental test in La Cerdanya.”

It should be noted that hunting within the national park is prohibited, although it is permitted in the area around this protected area.

Generalitat has been involved in this project by funding an action to eradicate trout from Lake Collada and soon plans to do the same to those in Travessani, all in the National Park.

The systems used are nets, shrimp farms and electric shocks that anesthetize them and make it easier to remove them one by one. Similarly, the CEAB-CSIC team is finalizing a pilot test for the use of fishicide, a biodegradable chemical already tested in other countries that inhibits gill respiration for animals, according to Ventura.

Calculations made on land indicate that in medium-sized ponds there can be between 500 and 1,500 trout and rainbow trout and up to 5,000 coal, while the number of minnows goes up to between 100,000 and 200,000. In France, they use the latter as bait and dump the surplus into the lakes.

The works will culminate in 2026 with the goal of restoring the species composition and ecological function of high mountain lakes in the Pyrenees, as well as in the Italian Alps, with the elimination of fish.