Scientists are delighted with the return of fish to the Sélune, a small river which has its source in the English Channel and flows into the bay of Mont-Saint-Michel.
The dam destruction project hydroelectric power plants of Vézins and La Roche-qui-Boit, located on the Sélune, in the South Manche, dates back to the Grenelle de l’environnement of 2007. It really came to fruition at the end of 2022 with the destruction of the second structure. Since then, in a few months, nature has reclaimed its rights and migratory fish have returned.
Researchers noticed this very quickly after the dams were destroyed. Laura Soisson, head of the Sélune scientific program at INRAE (National Research Institute for Agriculture, Food and the Environment), observes the return of Atlantic salmon.“It was reassembled almost at the same time as the work was completed, she says. And now, we have also seen that there is reproduction. So we can say that in less than a year after the dams were removed, migratory fish have indeed returned to areas that were closed to them until now.”
Better quality water
But salmon are not the only ones who can now swim upstream. Eels and sea lampreys have also found a larger habitat. “It is important for the conservation of the species, continues Laura Soisson. We are opening up new habitat and new potential breeding areas, particularly for salmon. These are also residence areas for eels, for example, which will spend most of their lives in the river. So this allows us to expand the habitat of these species a little. That’s why it’s important.”
The disappearance of these dams also benefits other species. “There was an issue with the quality of the water in the reservoir lakes, behind the dams. There was stagnant water and the production of toxic cyanobacteria, which caused big problems at the state level. environmental health”.
Mixed reactions from residents
However, despite these positive aspects, this project to destroy the Sélune dams encountered strong opposition from residents. Residents attached to these structures and their water retention. “Imagine that we change your landscape to which you have been accustomed since your childhood, explains Jean-Marc Roussel, research director at INRAE. This actually creates a reaction that I consider legitimate. Currently, what we are observing is a real recovery in the biodiversity of the entire valley, which for us is a fairly strong element in relation to the important work that has been carried out in this basin. .
Scientists will continue to observe the evolution of the river until 2027.