Almost a Quarter of All Freshwater Fish Species Are in Peril, Thanks to Humans.

Global analysis finds that development, overfishing, and pollution have made rivers dramatically different habitats than they were 200 years ago. 

The 18,000 types of fish living in rivers make up a quarter of all vertebrate species. After two centuries of industrial development, 23% of them are now threatened with extinction, according to new research published today in the journal Science. 

Individual rivers face different challenges, from overfishing in the Mekong River to increased damming along the Amazon, said Sébastien Brosse, a freshwater ecology professor at Paul Sabatier University in Toulouse, France. What this study does is quantify those challenges.

The French and Chinese scientists who contributed to the paper classified fish populations based on six scientific criteria including species and ecosystem function, which they then used to calculate a novel biodiversity index score—a “holistic measure of multiple measures of biodiversity change”— expressing humans’ impact on life in 2,456 river basins. More than 86% of rivers have been either moderately or severely affected by industrialization, with the remaining 13%, approximately, concentrated in tropical Africa and Australia. That’s far below the target many environmental organizations have set for conserving 30% of natural habitats by 2030. 

“This study provides support to the growing realization that the world is facing a freshwater biodiversity crisis, and humans are the primary cause,” said Julian Olden, an ecology professor at the University of Washington, who was not involved in the study. 

Overfishing, land use, redirected rivers, dams, soil and water pollution, and climate change have all contributed to the decline or extinction of native fish, as well as the rise of invasive species. That would be concern enough, the authors write. But the damage may impact the larger ecosystems that support much broader swaths of life and human industry. 

“Freshwater ecosystems are some of the most biodiverse places on the planet,” said Michele Thieme, lead freshwater scientist at World Wildlife Fund, who wasn’t a part of the study, “and we must protect them for the variety of services that they provide to nature and people.”

18 Februray 2021

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