The Convention on the Conservation of Migratory Species of Wild Animals (CMS), a crucial United Nations environmental treaty, has issued a stark warning about the accelerating breakdown of some of the planet’s most vital and lengthy animal migrations: those that unfold beneath the surface of the world’s rivers. A landmark report, released concurrently with the CMS’s 15th Meeting of the Conference of the Parties (COP15) in Brazil, paints a dire picture for migratory freshwater fish, identifying them as among the most threatened species globally. These aquatic travelers are not only integral to the health and functioning of riverine ecosystems but also underpin significant inland fisheries and provide essential food and livelihoods for hundreds of millions of people worldwide.
A Global Biodiversity Crisis Unfolding Beneath the Waves
The "Global Assessment of Migratory Freshwater Fishes," unveiled at COP15, underscores the urgent need for coordinated international action to protect hundreds of these remarkable species. The report presents compelling evidence that fish populations reliant on interconnected river systems that traverse national borders are experiencing rapid declines. The primary drivers identified include the pervasive impact of dam construction, leading to habitat fragmentation; widespread pollution from agricultural, industrial, and urban sources; unsustainable fishing practices; and the increasingly disruptive effects of climate change on aquatic ecosystems.
This comprehensive assessment has identified a staggering 325 migratory freshwater fish species as candidates for international conservation efforts. This figure highlights a largely overlooked biodiversity crisis that is unfolding across shared river systems, impacting species that have evolved to navigate vast aquatic networks. Beyond the 24 species already listed under the Convention’s Appendices I (requiring strict protection) and II (requiring international cooperation), these 325 species represent a significant expansion of the conservation imperative. The breakdown of these candidates by region reveals a global challenge:
- Africa: 40 species identified for potential inclusion.
- Asia: 106 species identified for potential inclusion.
- Europe: 44 species identified for potential inclusion.
- North America: 16 species identified for potential inclusion.
- South America: 119 species identified for potential inclusion.
It is important to note that the total number of species identified exceeds 325 because some species inhabit multiple continents, underscoring the transboundary nature of their migratory routes.
Key river systems have been pinpointed as critical priorities for conservation action, reflecting their immense ecological significance and the threats they face. These include South America’s mighty Amazon and La Plata-Paraná basins, Europe’s historically vital Danube River, Asia’s ecologically rich Mekong, Africa’s iconic Nile, and the Ganges-Brahmaputra system on the Indian subcontinent.
The report’s findings are based on an exhaustive analysis of extensive global datasets and IUCN (International Union for Conservation of Nature) assessments, encompassing nearly 15,000 freshwater fish species. This rigorous methodology provides the most detailed overview to date of the multifaceted conservation challenges confronting migratory freshwater fish. Crucially, the assessment also delineates practical, immediate steps that governments can and should implement. These include:
- Investing in sustainable infrastructure: Prioritizing the removal of unnecessary dams, the implementation of fish-friendly passage solutions at existing barriers, and ensuring that new infrastructure projects undergo rigorous environmental impact assessments that account for migratory needs.
- Strengthening transboundary cooperation: Establishing and reinforcing international agreements and joint management plans for shared river basins to ensure coordinated conservation strategies across national borders.
- Combating pollution: Implementing stricter regulations on industrial, agricultural, and municipal wastewater discharge, and promoting best practices to reduce non-point source pollution.
- Implementing sustainable fisheries management: Enforcing catch limits, seasonal closures, and gear restrictions to prevent overfishing, particularly of vulnerable migratory stocks.
- Restoring degraded habitats: Undertaking initiatives to reconnect floodplains, restore riparian vegetation, and improve water quality in critical spawning and nursery grounds.
- Addressing climate change impacts: Developing adaptation strategies to mitigate the effects of altered precipitation patterns, rising water temperatures, and increased frequency of extreme weather events on freshwater ecosystems.
The Neglected Freshwater Biodiversity Crisis
While declines in terrestrial and marine species often capture public attention, animals inhabiting freshwater ecosystems are experiencing even more rapid rates of reduction. However, the alarming collapse of migratory freshwater fish populations has, until now, received comparatively little global focus. These species depend intrinsically on long, unimpeded river pathways that connect essential life stages: spawning grounds, feeding areas, and the vital nursery habitats found in floodplains. These journeys often span vast distances and cross multiple national jurisdictions. When dams obstruct these routes, water flow regimes are unnaturally altered, or habitats degrade, fish populations can plummet with devastating speed.
The report’s projections are stark: migratory freshwater fish populations have declined by an estimated 81% globally since 1970. This represents a catastrophic loss of biodiversity and ecological function. Furthermore, the assessment reveals that nearly all (97%) of the 58 migratory fish species already listed by CMS (encompassing both freshwater and saltwater species) are now facing a significant threat of extinction.
The evidence unequivocally demonstrates that hundreds of migratory freshwater fish species are in a dire state of conservation. The report emphasizes a fundamental shift in perspective: effective conservation requires managing rivers as interconnected, flowing systems rather than treating them as separate national waterways. This holistic approach is paramount to preserving the integrity of these vital migratory corridors.
The Amazon Basin: A Critical Frontline for Conservation
As the host nation for COP15, Brazil has taken a leading role in advocating for enhanced conservation measures, particularly focusing on South America’s colossal river systems, the Amazon and the La Plata-Paraná. The Amazon Basin, one of the last remaining global strongholds for migratory freshwater fish, is facing mounting development pressures that threaten its unique ecological status.
A crucial case study, released in conjunction with the global assessment, highlights 20 migratory fish species within the Amazon that meet the criteria for potential inclusion under CMS Appendix II. These long-distance travelers are not merely ecologically significant; they are the backbone of regional fisheries, accounting for approximately 93% of total fish landings and supporting an industry valued at an estimated US$436 million annually.
Some of these Amazonian migrants undertake journeys of truly epic proportions. The dorado (gilded) catfish (Brachyplatystoma rousseauxii), a formidable bottom-dweller characterized by its metallic gold or silver sheen and substantial size (reaching up to 2 meters or 6.5 feet), completes the longest known freshwater migration of any fish species. Its complex life cycle involves an astonishing 11,000-kilometer (approximately 6,800 miles) odyssey from its spawning grounds in the Andean headwaters to coastal nursery areas, a testament to the interconnectedness of vast riverine landscapes.
To bolster conservation efforts, Brazil, in collaboration with other Amazonian nations, is proposing the development of a Multi-species Action Plan for Amazonian Migratory Catfish, slated for implementation between 2026 and 2036. This initiative exemplifies the type of regional cooperation necessary to address transboundary species conservation.
In parallel, Brazil has also proposed the addition of the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II. This proposal underscores the urgent need for coordinated action within the La Plata Basin, where this species is under severe threat from dam construction, altered water flow regimes, and intense fishing pressure.
Collectively, these proposed actions represent some of the most ambitious international endeavors yet undertaken to safeguard migratory freshwater fish. They firmly reinforce the central tenet of the CMS: that effective conservation solutions must encompass the entire geographic range of migratory species and are fundamentally dependent on robust cooperation between nations.
Expert Voices Call for United Global Action
The gravity of the situation has been underscored by leading figures in conservation science and policy.
Dr. Zeb Hogan, the lead author of the report, emphasized the hidden nature of these critical migrations: "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."
Amy Fraenkel, Executive Secretary of the CMS, highlighted the report’s significance in bringing a long-neglected issue to the forefront: "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."
Michele Thieme, Vice President and Deputy Lead of Freshwater at World Wildlife Fund-US, issued a powerful plea for immediate action: "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."
By the Numbers: The Global Scale of Migratory Fish Decline
The report provides a sobering statistical overview of the crisis:
- 81%: Estimated global decline in migratory freshwater fish populations since 1970.
- 97%: Percentage of CMS-listed migratory fish species (freshwater and saltwater) currently threatened with extinction.
- 325: Number of migratory freshwater fish species identified as candidates for international conservation efforts.
- 436 Million USD: Annual value of fisheries in the Amazon Basin heavily reliant on migratory fish species.
- 11,000 Kilometers: The extraordinary migratory distance undertaken by the dorado catfish (Brachyplatystoma rousseauxii), the longest known freshwater fish migration.
The release of the "Global Assessment of Migratory Freshwater Fishes" at COP15 marks a pivotal moment. It serves as a critical wake-up call, demanding that the international community recognize and urgently address the profound crisis facing these essential aquatic travelers. The interconnectedness of river systems necessitates a paradigm shift towards collaborative, basin-wide management strategies. Failure to act decisively and collectively will result in the irreversible loss of vital biodiversity, ecological services, and the livelihoods of millions who depend on healthy, thriving river ecosystems. The silent exodus of migratory freshwater fish is a stark indicator of the broader health of our planet’s freshwater resources, and their fate is inextricably linked to our own.
Documents related to the assessment and COP15 proceedings are available in English, Spanish, and French.
