A new United Nations report from the Convention on Migratory Species (CMS) finds that populations of migratory freshwater fish have declined by 81% since 1970, one of the largest drops recorded among major vertebrate groups and a faster fall than that of terrestrial and marine animals.
Drawing on assessments of nearly 15,000 freshwater fish species, the analysis concludes that nearly all (97%) of the 58 listed migratory fish species are threatened with extinction. The study identifies 325 species of freshwater fish that need international conservation action, noting that many traverse rivers crossing multiple borders.
The report links the rapid collapse to a combination of dam construction, river fragmentation, pollution, overfishing, and climate change impacts. Dams disrupt fish migrations by blocking upstream movement, altering river flows, and fragmenting river systems.
The Dorado catfish
The report highlights several river systems as particularly important for migratory fish, including the Danube, Amazon, Mekong, Nile, Ganges, and Brahmaputra, and calls attention to the La Plata–Paraná basin for coordinated efforts.
Populations of European eel and numerous sturgeon species have been decimated by dam construction and caviar harvest. The decline in global freshwater fish megafauna, including the Beluga Sturgeon, is estimated to be as high as 94 percent. Some species have already been lost: the Chinese paddlefish has been declared extinct.
The Dorado catfish of the Amazon can reach 2 meters. It migrates more than 10,000 kilometers. Their numbers have plummeted due to altered river flows, barriers, and overfishing.
In Asia, migratory freshwater megafish populations have declined by more than 95% since 1970. The Mekong giant catfish, capable of growing to over 295 kg, is now critically endangered due to dams blocking migration routes and overfishing at bottlenecks.
Food for 200 million people
Migratory fish support hundreds of millions of people worldwide and provide food for 200 million, BBC News reported.
“This assessment shows that migratory freshwater fish are in serious trouble, and that protecting them will require countries to work together to keep rivers connected, productive, and full of life,” said Zeb Hogan, the assessment’s lead author.
“Rivers do not recognize borders -- and neither do the fish that depend on them. The crisis unfolding beneath our waterways is far more severe than most people realize, and we are running out of time,” warned Michele Thieme, Vice President and Deputy Lead of Freshwater for the the World Wildlife Fund, The Guardian reported.