Migratory freshwater fish are collapsing worldwide, according to a new CMS report that highlights growing threats from dams, overfishing, pollution and climate change
By Coby Schlosberg
A new UN-backed assessment has warned that one of the world’s least visible wildlife crises is unfolding beneath the surface of its rivers. According to the Convention on the Conservation of Migratory Species of Wild Animals (CMS), the migration of freshwater species is collapsing at an alarming rate, threatening biodiversity, river health, food security and the livelihoods of hundreds of millions of people.
Migratory freshwater fish are among the most important yet most vulnerable species on Earth. They help maintain river health, support some of the world’s largest inland fisheries, and sustain communities across vast river basins. Yet freshwater ecosystems are declining faster than terrestrial or marine environments, making this an urgent but often overlooked global biodiversity crisis.
According to the report, migratory freshwater fish populations worldwide have declined by roughly 81 per cent since 1970, while 97 per cent of the 58 CMS-listed migratory fish species are threatened with extinction.
‘Many of the world’s great wildlife migrations take place underwater. 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 the report’s lead author, Dr Zeb Hogan.
The Global Assessment of Migratory Freshwater Fishes, launched at the CMS COP15 meeting in Brazil, identified hundreds of migratory fish species requiring cross-border action. Its findings suggest that species whose life cycles depend on connected rivers spanning national boundaries face mounting pressure from dam construction, habitat fragmentation, pollution, overfishing and climate-driven ecosystem change.
In total, 325 migratory freshwater fish species were identified as candidates for coordinated international conservation efforts. Priority river basins include South America’s Amazon and La Plata–Paraná, Europe’s Danube, Asia’s Mekong, Africa’s Nile and the Ganges–Brahmaputra system on the Indian sub-continent.
CMS scientific experts drew on extensive global datasets and International Union for Conservation of Nature (IUCN) assessments of nearly 15,000 freshwater fish species. The report provides the most comprehensive overview yet of the conservation needs of migratory freshwater fish.
Among its recommendations are immediate measures to protect migration corridors and environmental flows, implement basin-scale action plans and better coordinate seasonal fisheries management.
Many migratory fish depend on long, uninterrupted river corridors, often stretching across several countries, to reach spawning grounds, feeding areas and floodplain nurseries. But dams, altered river flows and habitat degradation are breaking these connections, driving population declines.
‘Rivers don’t recognise borders – and neither do the fish that depend on them. The crisis unfolding beneath our waterways is far more severe than most people realise, and we are running out of time. 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,’ said Michele Thieme, Vice President and Deputy Lead of Freshwater at WWF-US.
How can South America’s rivers be improved?
The Amazon Basin – the largest drainage system in the world – is increasingly under pressure from development, threatening its status as one of the planet’s most important strongholds for migratory freshwater fish.
A case study released alongside the global assessment identified 20 migratory fish species in the Amazon that meet the criteria for possible inclusion on CMS Appendix II. They were found to have an unfavourable conservation status and to require international agreements for their conservation and management.
These species are known for undertaking some of the longest freshwater migrations ever recorded. The dorado catfish (Brachyplatystoma rousseauxii), for example, can travel as far as 11,000km.
A ten-year regional action plan for catfish has been proposed to encourage cooperation between the countries that share the basin.
Brazil is also recommending the addition of the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II, underlining the need for coordinated action in the La Plata basin, where dams, altered flows and fishing pressures are contributing to a worsening biodiversity crisis.
