Campo Grande, 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, according to a major new assessment by the Convention on the Conservation of Migratory Species of Wild Animals (CMS), an environmental treaty of the United Nations.
The Global Assessment of Migratory Freshwater Fishes, being launched at the CMS 15th Meeting of the Conference of the Parties (COP15) in Brazil, finds that migratory freshwater fish — a group of species that maintain river health, underpin some of the world's largest inland fisheries, and sustain hundreds of millions of people — are among the most imperiled wildlife on the planet.
The Assessment identifies hundreds of migratory fish needing cross-border action, presenting authoritative evidence that species whose life cycles depend on connected rivers across national borders face accelerating declines driven by dam construction, habitat fragmentation, pollution, overfishing and climate-driven ecosystem changes.
The analysis identifies 325 migratory freshwater fish species as candidates for coordinated international conservation efforts, highlighting a largely overlooked biodiversity crisis unfolding across the world's shared river basins.
A regional breakdown of the 325 migratory freshwater fish species deemed candidates for international protection (beyond the 24 already listed) under the Convention's Appendices I (species requiring strict protection) and II (species needing international cooperation):
- Asia: 205
- South America: 55
- Africa: 42
- Europe: 50
- North America: 32
(The total adds to more than 325 because some species occur on multiple continents.)
Priority river basins include South America's Amazon and La Plata–Paraná, Europe's Danube, Asia's Mekong, Africa's Nile, and the Indian sub-continent's Ganges–Brahmaputra.
Prepared by CMS scientific experts using extensive global datasets and IUCN assessments of nearly 15,000 freshwater fish species, the report provides the most comprehensive overview yet of migratory freshwater fish conservation needs.
It also outlines practical tools governments can deploy immediately, including:
- protection of migration corridors and environmental flows,
- basin-scale action plans and transboundary monitoring, and
- coordinated seasonal fisheries
A global crisis largely hidden beneath the waterline
Populations of animals inhabiting freshwater ecosystems are declining faster than populations of terrestrial and marine animals, yet the collapse of migratory freshwater fish populations has received little international attention.
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.
According to the report, 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.
The new assessment deepens that picture, identifying hundreds of migratory freshwater fish with an unfavourable conservation status and underlines that protecting migratory fish requires managing rivers as connected systems rather than isolated national waterways.
Spotlight on South America's great rivers
Host of COP15, Brazil is proposing several conservation measures related to South America's two largest river systems, the Amazon and La Plata–Paraná.
The Amazon Basin remains one of the last great strongholds for migratory freshwater fish, but intensifying development pressures threaten that status.
A case study released along with the new global assessment identifies 20 migratory fish species in the Amazon meeting criteria for potential CMS Appendix II listing. These large long-distance migrants are flagships for the river's migratory fish, which account for roughly 93% of fisheries landings, underpinning regional fisheries valued at an estimated US$436 million annually.
They are also famed for undertaking some of the longest freshwater migrations ever recorded. Among them is the dorado (gilded) catfish (Brachyplatystoma rousseauxii), a bottom-dweller known for its metallic gold/silver skin and impressive size (up to 2 meters / 6.5 ft), highly prized in commercial fisheries. Renowned for the longest life cycle freshwater migration of any fish, its journey spans 11,000 kilometers, from Andean headwaters to coastal nurseries.
To strengthen conservation, Brazil and other governments are proposing a Multi-species Action Plan for Amazonian Migratory Catfish (2026–2036), developed through regional cooperation involving multiple countries.
Brazil has also proposed adding the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II, highlighting the need for coordinated action in the La Plata Basin, where they are threatened by dams, altered flows and fishing pressures.
Together, the initiatives rank among the most ambitious international efforts yet to safeguard migratory freshwater fish species and reinforce the central purpose of CMS: conservation solutions for migratory species must operate across the full range of the species, and require international cooperation to succeed.
Comments
Lead Author Dr. Zeb Hogan:
"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."
CMS Executive Secretary Amy Fraenkel:
"This new assessment highlights a major priority for the conservation of migratory species and their habitats, that has not had adequate focus to date. By aligning science, policy and international cooperation, governments can safeguard the world's remaining great freshwater fish migrations and the communities and ecosystems that depend on them."
World Wildlife Fund-US, Vice President and Deputy Lead of Freshwater, Michele Thieme
"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. 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."
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The hidden collapse of the world's great freshwater migrations
By the numbers
325: Migratory freshwater fish species identified as candidates for coordinated international conservation action under the CMS (beyond the 24 species already listed in Appendices I and II).
205: Species identified in Asia alone, making it the global hotspot for migratory freshwater fish at risk.
81%: Estimated decline in migratory freshwater fish populations worldwide since 1970, one of the steepest drops recorded for any major vertebrate group.
97%: Share of CMS-listed migratory fish already threatened with extinction.
15,000: Freshwater fish species assessed through the IUCN Red List and global datasets used to produce this assessment, the most comprehensive evidence base ever assembled for migratory freshwater fish.
250+: Transboundary rivers and lakes worldwide, meaning conservation success depends on cooperation between countries rather than national action alone.
47%: Approximate share of Earth's land surface lying within shared river basins.
93%: Proportion of Amazon fisheries landings made up of migratory freshwater species, highlighting their critical role in regional food systems and livelihoods.
US$436 million: Estimated annual value of Amazon fisheries based on migratory species
20: Amazon Basin species identified as meeting criteria for potential CMS Appendix II listing in the new case study.
10,000+ kilometres: Migration distance of the dorado (gilded) catfish — among the longest freshwater migrations ever recorded.
1 fundamental solution: Managing rivers as connected ecological systems rather than isolated national waterways.
