Technology Biodiversity: the population of migratory fish in free fall

Biodiversity: the population of migratory fish in free fall

The National Federation of Fishing in France is calling to save migratory fish.

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The population of migratory fish – salmon, sturgeon or eel – has fallen by 93% in Europe since the 1970s. A collapse that is all the more striking as these fish are normally very good at survival.
Capable of traveling several thousand kilometers between oceans and rivers to reproduce, they are equipped with a magnetic navigation system to locate themselves and can move at speeds of up to 80 km/h. They are able to survive in both fresh and salt water. These performances are out of the ordinary and yet they are withering away. The sturgeon, the eel and the great shad are even among the species in critical danger of extinction, in the same way as the polar bears, the red pandas or the tigers.

This is no longer the main threat, explains Eric Feunteun, professor of marine ecology at the Museum of Natural History, because a lot of effort has been made over the past ten years. Today, the problem comes rather from the increase in temperatures and the pollution of rivers by pesticides, drugs, metals. There is also the question of dams, whether it is a small reservoir one meter high or a hydroelectric installation. In France, there is a dam every 5 km, so many obstacles that the fish must cross at all costs when they go up the rivers to reproduce because when they do not succeed, they become exhausted or become swallowed by predators.

There are fish passes, which allow you to circumvent these dams, but it does not work 100%. Because unfortunately not all the fish find the entrance to this second route to protect them. According to a study carried out on the Vienne, only one in three fish manages to use these passes and the problem is then the return downstream with the passage of the turbines in the other direction, which leads to 10 to 30% mortality. .

It is possible to help these migratory fish reproduce in a protected environment, then release them afterwards. This is a solution to try to perpetuate the species, but once reintroduced into the natural environment, the question of their long-term survival arises. It is therefore of course on the overall protection of rivers that action must now be taken.

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