Hidden 'Beneath the Surface,' Freshwater Fish Migrations Collapsing Worldwide

More than 300 species of migratory freshwater fish are in dire need of "urgent coordinated cross-border collaboration" amid a crisis of rapid collapse, according to a report released Tuesday at a key United Nations conservation conference in Brazil.

"Some of the longest, most important migrations of species on Earth are happening beneath the surface of the world’s rivers and many are rapidly collapsing," the United Nations Convention on the Conservation of Migratory Species of Wild Animals' (CMS) annual "Global Assessment of Migratory Freshwater Fishes" report states.

Released at CMS' 15th Meeting of the Conference of the Parties (COP15) in Campo Grande, Brazil the report details how freshwater fish—which are vital for the health of riparian ecosystems and provide food for hundreds of millions of people around the world—"are among the most imperiled wildlife on the planet."

"Many migratory species now face declines driven by loss of connectivity, flow alteration, habitat degradation, exploitation, pollution, and interacting pressures across borders," the report notes. "Recognizing these trends and their transboundary nature, [CMS] has sought stronger coordinated action for inland fishes that move across national jurisdictions."

The report's authors—Zeb Hogan, Zach Bess, Michele Thieme, and Twan Stoffers—identified 325 species of freshwater fish as candidates for international conservation efforts. River basins the report says should be prioritized include the Amazon and La Plata–Paraná in South America, the Danube in Europe, the Mekong and Ganges-Brahmaputra in Asia, and the Nile in Africa.

According to the report:

Many migratory fish rely on long, uninterrupted river corridors connecting spawning grounds, feeding areas, and floodplain nurseries, often across multiple countries. When dams, altered flows, or habitat degradation interrupt those pathways, populations can decline rapidly...

Migratory freshwater fish populations worldwide have declined by roughly 81% since 1970 and nearly all (97%) of the 58 CMS-listed migratory fish species (including fresh and salt-water species) are threatened with extinction.

CMS recommends governments take steps to safeguard migratory fish and their habitats, including protecting migration corridors, devising basin-scale action plans and transboundary monitoring, and international coordination of seasonal fisheries.

“Many of the world’s great wildlife migrations take place underwater," Hogan, the report's lead author, said in a statement. "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.”

Thieme, who is vice president of World Wildlife Fund-US, said that “rivers don't 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," she added. "Rivers need to be managed as connected systems, with coordination across borders, and investments in basin-wide solutions now before these migrations are lost forever."

The CMS report follows last month's publication of a study by researchers in Spain who examined how ocean warming driven by human burning of fossil fuels is causing a "staggering and deeply concerning loss of marine life.”