to protect biodiversity, a “fish pass” will be installed on the Rhône

On the occasion of International Biodiversity Day, Wednesday May 22, focus on this kind of giant staircase for fish in Villeurbanne.

On a large river like the Rhône, biodiversity is preserved by “fishways”. This is a way to help fish move upstream to their breeding grounds. One of these works is currently under construction by the Compagnie Nationale du Rhône (CNR), the concessionary company of the river, upstream from Lyon to Villeurbanne.

Here, the Rhone reaches a flow rate of up to 23 m3 per second. Under the effect of the so-called Feyssine threshold, this small waterfall of 1.50 meters poses a problem to certain fish. “Not for the most athletic fish, like barbel or trout, but for all other fish which are more vulnerable and which have low capacities… This fall is an obstacle which is insurmountable”, assures Said Herrouch. He is the project manager of this imposing “fishway”: 160 meters long and 10 meters wide. “By a system of steps, we have divided this fall into eleven small falls, all less than fifteen centimeters. And step by step, the fish will cross the 1.50 meter which separates it from the upstream in complete safety “, he assures.

The investment – amounting to 6 million euros – is co-financed by CNR and the Rhône Méditerranée Corse water agency. Public concerned: some 200,000 fish each year, estimates Compagnie nationale du Rhone, or 25 different species. “It ranges from calm water species, like carp or roach, to white water species: brown trout, brown trout, common grayling… The idea is that everyone can have different speeds. adapted to its crossing abilities: those who will jump, those who will swim in open water or those who will swim at the bottom“, specifies Said Herrouch.

This work is a tool for safeguarding biodiversity, assures Franck Pressiat, head of the environment department at the CNR: “It allows species either to migrate for their reproduction, or to seek food or environmental conditions that suit them better elsewhere by going from one place in the Rhône to another, also passing from the Rhône to tributaries. And all this allows them to have more resilience when there are environmental changes.”

“Reports at the national and international level show serious declines in biodiversity, particularly in aquatic environments”

Franck Pressiat, CNR manager

at franceinfo

“We are hopeful, adds Franck Pressiatthat in the years to come – with all these efforts on continuity, on crossing works, combined with efforts from the world of fishing and reduction of all pressures – we will manage to rebuild populations of migratory fish consequences which themselves are then beneficial for all of the river’s ecosystems.”

Several thousand fish will be monitored using a chip to assess the real impact of this pass which will be put into service at the end of 2024. Within ten years, the entire Bas-Rhône will be equipped with “fish passes”. that is to say the entire area which goes from Lyon to the Mediterranean.