One-quarter of freshwater fish are at risk of extinction, new assessment finds

One-quarter of the world's freshwater fish are at risk of extinction, according to the first comprehensive assessment of the animals by the world's leading scientific authority on the status of species.

The findings, issued Monday by the International Union for Conservation of Nature at the UN climate summit in Dubai, United Arab Emirates, are part of the organization's latest update to its Red List of Threatened Species. They came as an array of scientists, advocates and ministers attending the negotiations were urging nations to tackle the global biodiversity crisis in tandem with global warming.

Healthy ecosystems store planet-warming carbon while nurturing wild animals, plants and fungi, providing a double win for climate and biodiversity. If natural areas are destroyed, losses are inflicted on both fronts.

As climate change intensifies, it bears down on wildlife already experiencing staggering declines.

The assessment found that the biggest threat to freshwater fish was pollution, affecting 57 per cent of the imperiled species in the group. The pollution comes from fertilizers and pesticides running off farm fields, from sediment clogging up rivers and streams after land has been cleared and from human sewage and industrial waste.

Dams and water extraction came in second, menacing 45 per cent of threatened freshwater fish. Overfishing, invasive species and disease also take a toll.

"Climate change really compounds all of the other threats," said Catherine Sayer, who leads the group's freshwater biodiversity program.

The update included evaluations of 1,640 species of freshwater fish that had never been assessed before, bringing the total to 14,898. That met the threshold of 80 per cent of known species in the group, the point at which the IUCN considers a group of species to be comprehensively assessed.

Atlantic salmon, which begin and end their lives in the rivers and streams of North America and Europe, moved from being considered a species of least concern to being classified as near threatened. New evidence suggests that their global population decreased 23 per cent between 2006 and 2020, with climate change affecting them at all life stages. Dams cut them off from spawning and feeding grounds. Pollution from agriculture and logging kills their young.

Gilded catfish, a commercially important species that migrates thousands of miles from the estuaries of the Amazon and Orinoco rivers to the Andean foothills and back, and that was previously in the category of least concern, is now classified as vulnerable. Hydroelectric dams planned for the Madeira River Basin in Brazil and Bolivia are projected to cause a population decline of at least 37 per cent within the next two decades.

And a small, orange and blue iridescent species of killifish from Mozambique, assessed for the first time, was classified as endangered, threatened by expanding agriculture and graphite mining.

The assessment of freshwater fish adds to a grim trend for biodiversity worldwide. While public attention has long focused on charismatic mammals and birds, there's increasing scientific awareness of alarming declines in all kinds of groups. Amphibians appear to be the most imperiled of vertebrates, with 40 per cent threatened with extinction, and with their status deteriorating globally. For reptiles, it's 20 per cent. Invertebrates are even harder to assess and protect.

Then, there are the plants. While a global tree assessment is ongoing, current data shows that one-third of all tree species are imperiled.

Monday's Red List announcement included an update to the status of big leaf mahogany, long prized for its fine wood. Threatened by illegal logging throughout its native range, from Mexico southward to Brazil and Bolivia, it moved from the vulnerable category to the more dire endangered category.

"Trees aren't thought of as a finite resource," said Megan Barstow, who worked on the assessment through her position at Botanic Gardens Conservation International, an umbrella group that seeks to prevent plant extinctions. "People don't think of timber products as a wildlife product."

Scientists emphasize that good conservation works. In fact, two of the species in Monday's update are success stories. The scimitar-horned oryx, an antelope whose horns live up to its name, shifted from extinct in the wild to endangered, following efforts to reintroduce the species in Chad. The saiga, an antelope with a cartoonish profile that is found in Kazakhstan, Mongolia, Russia and Uzbekistan, went from critically endangered to near threatened.

The successes were because of strong collaborations among governments, nonprofit groups, scientific experts and local communities, according to David Mallon, co-chairman of IUCN's antelope specialist group.

A year ago, nations of the world agreed on a series of commitments to stanch biodiversity loss, including protecting 30 per cent of Earth's lands, freshwater and oceans by 2030. This month, UN officials are expected to issue information on what countries have done so far.

On Saturday in Dubai, the country leading the current climate negotiations, the UAE, and the country that led last year's biodiversity talks, China, called on nations to integrate and align their plans to rein in climate change and biodiversity loss.