The Loire, the last great wild river in Europe

The Loire is a bit like the “rebellious teenager” of French rivers. There are few developments, few dams, few dikes too. It is used to rapid and significant floods, but it is also a temple of biodiversity. A unique flora and fauna, today threatened by climate change which favors the appearance of green algae and invasive species.

Due to the sanitary situation, the exchanges will take place online, but these three days of conferences and debates should allow us to reflect on the consequences of hydroclimatic changes on the life of highly migratory amphihalines, these fish that pass from fresh water. with salt water, during their lifetime and vice versa. This is the case, for example, of the salmon which lives in the sea and goes up rivers to go to spawn.

Conversely, the eel lives between 5 and 10 years in fresh water, and when it becomes adult, it takes a silvery color and returns to the sea to lay eggs. Amphihaline species are all affected by global warming, underlines Marion Legrand, in charge of the migration program of the Loire basin within the association “Loire Grands Migrateurs”

This is the case in particular with salmon which is a cold water fish. It grows off Greenland for several years, and when it leaves its marine life to join a river or a river, it will always seek to get closer to the sources to have fresh water.

It is a species particularly sensitive to temperature changes.
This is also the case for shad, a migratory fish that is also found in the Loire basin. These are species that have specific needs in terms of temperature, and any change in the universe is important.

“In general, amphihaline fish are all threatened.”

Marion legrand

to franceinfo

And to quote the red list established in 2019 by the‘International Union for the Conservation of Nature. The IUCN estimates that 55% of amphihaline species are classified in the “threatened” category, in particular the European eel and the great shad found in the Loire. The sturgeon that does not live in the Loire basin is clearly in critical danger of extinction, according to the organization.

Marion Legrand explains that amphihaline migrants have an extraordinary ability to adapt to a new environment, especially since they are mobile and can travel several thousand kilometers in order to choose a new place to live and reproduce. These species even manage to get used to temperature changes.

We are used to saying that the Loire is rather privileged in terms of dams or obstacles for fish. On the main watercourse of the river one can do more than 500 kilometers without finding any important dam, which is not true on its tributaries, where one finds a multiplication of obstacles which thwart the life of the migrants.

Salmon are always looking for a specific area to spawn. The species needs to go up very high in the Loire basin. If it does not migrate 700 kilometers, it will have difficulty finding suitable breeding habitat. We therefore understand very well that dams are a problem for the respect of the life cycle of its amphihaline migrants.