Migratory freshwater fish populations across the world have declined by nearly 81 per cent since the 1970s and roughly 97 per cent of the 58 listed migratory fish species under the Convention of Migratory Species (CMS) are threatened with extinction.
These fish species, comprising of fresh and salt-water species, are rapidly collapsing, putting ecosystems at risks and threatening fisheries and livelihoods of millions of people worldwide.
These findings were revealed in a report launched on March 24 at the Convention on the Conservation of Migratory Species’ COP15 in Brazil and is a comprehensive update to a 2011 review.
The Global Assessment of Migratory Freshwater Fishes identifies 325 species requiring coordinated international conservation action due to declines driven by dams, habitat fragmentation, pollution, overfishing, and climate change, the report said.
Of these species identified under the Convention’s Appendices I (species requiring strict protection) and II (species needing international cooperation), 205 were recorded in Asia, 55 in South America and 42 in Africa. Europe and North America documented 50 and 32 species respectively. The total amounts to over 323 as some species are found on multiple continents.
Of the candidates, 136 species are categorised as threatened (Critically Endangered, Endangered, or Vulnerable) or Near Threatened by the International Union for Conservation of Nature. At least 75 of these threatened species occur in two or more CMS Parties, making them strong candidates for immediate listing and international cooperation.
“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,” a press statement said.
The report highlighted that the crisis is hidden under the water as these recorded population declines are faster compared to populations of terrestrial and marine animals, but the wiping of migratory freshwater fish populations receive less international attention.
The analysis noted priority river basins which 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 where cooperation is vital.
It said the Amazon and La Plata Basins, home to extreme long-distance migrants and various characids, require basin-scale connectivity.
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 kilometres, from Andean headwaters to coastal nurseries, the authors noted.
The Danube Basin is crucial for potamodromous cypriniforms and remaining sturgeon populations that connect 19 countries.
The assessment said the Mekong basin is significant for inland fisheries but faces existential risks from dam expansion and many of its key migrant species like the Mekong giant catfish are already Critically Endangered.
According to the report, sturgeons and paddlefishes remain the most threatened vertebrate group. The Chinese paddlefish was officially confirmed extinct in 2022, the first CMS-listed fish lost.
The authors underlined the need to protect Anguillid Eels as their catadromous life cycles (Fishes that spend most of their lives in fresh water but breed in the sea) connect ocean spawning grounds to headwater habitats across multiple island states, requiring regional passage standards.
They further suggested moving species to Appendix I or II to increase protection or add coordinated management. The report also suggested bringing fish conservation into mainstream with themes linked to connectivity, and strengthening ties with other conventions like CITES and the Convention on Biological Diversity (CBD).
Brazil has 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, the statement said.
Lead author Zeb Hogan in a press statement said, “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.”
The new assessment identifies 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.