Humans have severely affected fish biodiversity in half of all rivers 

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The Mississippi River near Brainerd, Minnesota

The Mississippi river near Brainerd, Minnesota

Daniel Thornberg/Alamy

Fish biodiversity in freshwater systems, such as lakes and rivers, has been declining since the beginning of the industrial revolution – so much so that researchers now estimate human activity has severely affected the fish biodiversity in more than half of the world’s rivers.

Our planet’s rivers and lakes provide a habitat for nearly 18,000 fish species, despite covering less than 1 per cent of Earth’s surface. Sébastien Brosse at Paul Sabatier University in Toulouse, France, and his colleagues have been collecting data from 2456 river basins across the world for more than a decade.

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These basins host over 14,000 fish species, which is more than 80 per cent of the global freshwater fish pool.

Brosse and his team created an index to measure the changes in fish biodiversity in these rivers and how they have been affected by human activity. Previous measures of biodiversity typically only assessed the number of different species in a particular ecosystem. This new index also measures the function of each freshwater species and their evolutionary relationships.

Using these measures, each river basin was given a score between 0 and 12 – the higher the score, the higher the change in biodiversity as a result of human activity.

The team found that 53 per cent of the river basins had a score higher than 6, meaning their fish biodiversity had been severely affected by human activities, especially after the industrial revolution. Unsurprisingly, these were located mostly in high-income countries, such as western Europe and North America, where humans have heavily manipulated rivers.

Just 14 per cent of river basins in the study have been little affected by human activity, but these only provide a habitat for one-fifth of the world’s freshwater fish species.

“The less-impacted rivers are mainly located in Africa and Australia,” says Brosse. This is probably due to a slower rate of industrialisation in Africa and low population density around rivers in Australia, he says.

“Rivers which have the most economic development around them, like the Mississippi river, are the most strongly impacted,” says Brosse. Along with overfishing and climate change, dams are especially harmful for freshwater biodiversity as they reduce the flow of nutrients and block migrating fish.

Sustaining fish biodiversity is important for many communities who consume a lot of fish, says Richard York at the University of Oregon. “For example, in Cambodia, more than 60 per cent of the protein in diets is supported by freshwater fish,” says Brosse.

Journal reference: Science, DOI: 10.1126/science.abd3369

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