The Oyapock River, border between French Guiana and Brazil, one of the few rivers in South America whose fish biodiversity is still little modified by human activities.

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Sébastien Brosse - EDB

  • Between extinctions of certain species and introductions of others, or even overfishing, the biodiversity of the world's waterways has changed a lot over the last two centuries.

  • Scientists, coordinated by Toulousain Sébastien Brosse, have developed a new indicator of biodiversity.

  • The results, published in the journal

    Science

    , show that only 14% of the world's rivers have been little impacted by human activity.

A century ago, salmon and sturgeons spawned in the Garonne without anyone caring to see them one day disappear.

Today, victims of overfishing, of the deterioration of their environment but also of new predators introduced by man such as catfish, these two species are in danger.

And they are not the only ones for two centuries to be on the verge of extinction in the world's waterways.

“There are 170 cases of extinctions attested in the world, but we are very far from the account because for this to be attested we must not have seen the species for ten years.

There is a report from the IUCN [The International Union for the Conservation of Nature] which has just been released and corroborates our results ”, indicates Sébastien Brosse, professor at the University of Toulouse III - Paul Sabatier and member of the Evolution laboratory. and biological diversity (CNRS / Université Toulouse III - Paul Sabatier / IRD).

With his team, he has just developed a new biodiversity indicator to know the impact of human activity, where he takes into account both the number of species, their role but also their kinship links between them to observe the changes.

Their first results have just been published in the journal

Science

and they are unstoppable: if more than 50% of the 2,456 rivers of the globe, considered in the study, had their fish faunas strongly modified by human activities , only 14% remain little impacted and they shelter only 22% of the species of freshwater fish of our planet.

Preserved waterways

Ratings were thus given, from zero, where no indicator is impacted, up to twelve, where they all are.

“There is 14% of the world's surface rivers that have changed little and have a rating of three or less.

They had no local change, recorded no extinction, or introduction of species.

They are found in areas where there are few humans or economic activities, in tropical areas, such as the Amazon, Central Africa, part of Southeast Asia, the north of the 'Australia and a few rivers in the far north of the northern hemisphere,' explains Sébastien Brosse.

None reach zero level, as there is always a surrounding stream to negatively impact it.

No need to hope to be on the honor roll for our rivers and streams in Western Europe or North America.

The Garonne inherits an 11/12 when the Thames takes down the pompom with a 12/12.

And there, there is therefore no question of validated extinctions.

“In total, there are 4,000 species listed as endangered, and which will most likely disappear.

If we take the European sturgeon, there are only a few thousand individuals left in the Garonne estuary, it is very soon.

This already marked change in biodiversity is really a first warning that risks being followed by a more marked decline, ”continues the scientist.

Political decisions

And in parallel with these extinctions due to human pressure, what made the wealth of endemic fauna will be impoverished to move towards more and more homogeneous aquatic ecosystems.

If turning back seems very complicated, citizen awareness of the decline in biodiversity exists.

“But we would need strong political decision making.

We could think of more drastic measures to try to exclude invasive species, one of the causes of the decline in biodiversity.

This could also involve blowing up dams or even reducing our discharges, but also overexploitation, ”concludes Sébastien Brosse.

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