Some of the longest and most essential animal migrations on Earth take place beneath the surface of rivers, a hidden world of movement critical for ecological balance and human well-being. However, a major new report from the Convention on the Conservation of Migratory Species of Wild Animals (CMS), a United Nations environmental treaty, warns that many of these vital migrations are now rapidly breaking down, signaling a largely overlooked global biodiversity crisis.
Released at the CMS 15th Meeting of the Conference of the Parties (COP15) in Brazil, the "Global Assessment of Migratory Freshwater Fishes" paints a grim picture, identifying migratory freshwater fish as among the most threatened species worldwide. These fish are not merely components of aquatic ecosystems; they are foundational to maintaining healthy rivers, supporting major inland fisheries that feed hundreds of millions, and providing essential food security and livelihoods for vulnerable communities across the globe.
The Unseen Crisis Beneath the Waves
The report represents the most comprehensive overview to date of the conservation challenges confronting migratory freshwater fish. Drawing on extensive global datasets and IUCN assessments of nearly 15,000 freshwater fish species, it underscores a profound and accelerating decline. Animals inhabiting freshwater ecosystems are experiencing a faster rate of decline than their terrestrial or marine counterparts, yet the precipitous collapse of migratory freshwater fish populations has historically received disproportionately little global attention.
Migratory freshwater fish depend on long, uninterrupted river pathways that connect crucial spawning grounds, nutrient-rich feeding areas, and sheltered floodplain nurseries. These pathways frequently traverse multiple national borders, highlighting the inherent transboundary nature of their existence and the complex conservation challenges they present. When these vital connections are severed or degraded by human activities, populations can plummet with alarming speed.
The assessment reveals that migratory freshwater fish populations have plummeted by an estimated 81% worldwide since 1970. The situation is even more dire for species already recognized by CMS; nearly all (97%) of the 58 CMS-listed migratory fish species (which include both freshwater and saltwater species) are currently facing the threat of extinction. This dramatic decline underscores a systemic failure to protect these species and the intricate river systems they inhabit.
Drivers of Decline: A Multifaceted Threat
The primary drivers behind this staggering decline are multifaceted and interconnected, reflecting the pervasive impact of human development on riverine environments. The report provides strong evidence that fish relying on connected rivers across national borders are declining quickly due to:
- Dam Construction and Hydropower Development: Thousands of dams worldwide fragment river systems, blocking migration routes and altering natural flow regimes, which are critical for spawning cues and habitat availability. An estimated one-third of the world’s large rivers are now fragmented, isolating fish populations and preventing them from completing their life cycles.
- Habitat Fragmentation and Degradation: Beyond dams, river habitats are degraded by deforestation, agriculture, urbanization, and sand and gravel extraction, leading to loss of critical spawning and feeding grounds.
- Pollution: Industrial, agricultural, and domestic pollution contaminates river waters, impacting fish health, reproductive success, and the overall aquatic food web. Chemical runoff, plastic waste, and pharmaceutical byproducts all contribute to a toxic environment for sensitive migratory species.
- Overfishing: Unregulated or poorly managed fisheries exert immense pressure on migratory fish stocks, particularly as they concentrate during migrations or at spawning sites. The economic value of these fish often drives unsustainable harvesting practices.
- Climate-Related Ecosystem Changes: Shifting water temperatures, altered precipitation patterns, and increased frequency of extreme weather events (droughts and floods) disrupt the delicate environmental cues that migratory fish rely on, affecting their behavior, survival, and reproductive cycles.
A Call for Coordinated Global Action
In response to this deepening crisis, the assessment highlights hundreds of migratory fish species that urgently require coordinated international action. In total, 325 migratory freshwater fish species have been identified as candidates for international conservation efforts, a figure that significantly expands beyond the 24 species already listed under CMS Appendices I (species requiring strict protection) and II (species needing international cooperation). This substantial number points to a largely overlooked biodiversity crisis unfolding across shared river systems globally.
Key river systems identified as priority areas for intervention 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. These iconic rivers, which are lifelines for millions of people and countless species, are also among the most threatened by human activity.
Practical Pathways to Conservation
The report also outlines practical and immediate steps that governments can take to reverse the trend. These actions emphasize managing rivers as integrated, connected systems rather than isolated national waterways:
- Remove Obsolete Barriers and Improve Fish Passage: Prioritize the decommissioning of defunct dams and implement effective fish ladders or bypasses at essential barriers to restore connectivity.
- Restore Degraded River Habitats and Floodplains: Undertake large-scale restoration projects to revive natural river channels, riparian zones, and floodplain habitats crucial for different life stages of migratory fish.
- Implement Stricter Pollution Controls: Enforce robust regulations on industrial, agricultural, and municipal discharges to significantly reduce contaminants entering freshwater systems.
- Establish and Enforce Sustainable Fishing Quotas: Develop and implement scientifically sound management plans that include catch limits, seasonal closures, and gear restrictions to prevent overfishing.
- Integrate Migratory Fish Conservation into National Development Plans: Ensure that infrastructure projects, agricultural policies, and urban development consider and mitigate their impacts on river connectivity and aquatic biodiversity.
- Invest in Transboundary River Basin Management: Foster international agreements and collaborative frameworks for shared river basins, recognizing that fish migrations transcend political borders.
- Develop and Utilize Robust Monitoring and Research Programs: Invest in scientific research to better understand migratory patterns, population dynamics, and the specific threats facing individual species, informing adaptive management strategies.
- Raise Public Awareness and Engagement: Educate local communities, policymakers, and the general public about the ecological and economic importance of migratory freshwater fish and the urgency of their conservation.
Spotlight on the Amazon: A Critical Battleground
As the host of COP15, Brazil has taken a leading role, proposing several crucial conservation measures focused on South America’s largest river systems, the Amazon and La Plata-Paraná. The Amazon Basin remains one of the last major strongholds for migratory freshwater fish, boasting unparalleled biodiversity. However, escalating development pressures, including new dam projects, mining, and deforestation, are rapidly jeopardizing this status.
A detailed case study released alongside the global assessment identifies 20 migratory fish species in the Amazon that meet the criteria for potential CMS Appendix II listing. These long-distance migratory species are not just ecologically significant; they are central to regional fisheries, constituting approximately 93% of total landings and underpinning an industry estimated to be worth US$436 million annually. The potential loss of these species carries severe economic and social ramifications for the millions of people in the region who depend on them.
Among these remarkable species is the dorado (gilded) catfish (Brachyplatystoma rousseauxii), a bottom-dwelling species with striking metallic gold/silver coloring and an impressive size, capable of reaching up to 2 meters (6.5 ft) in length. This species undertakes the longest known freshwater migration of any fish, with its life cycle involving an extraordinary journey of 11,000 kilometers from Andean headwaters to coastal nursery areas. Such epic migrations underscore the vast, interconnected nature of these river systems and the devastating impact of any disruption along their path.
To strengthen conservation efforts, Brazil, in collaboration with other regional nations, is proposing a Multi-species Action Plan for Amazonian Migratory Catfish (2026-2036). This initiative highlights the critical role of regional cooperation in protecting species that inherently cross national boundaries. Brazil has also proposed adding the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II, emphasizing the urgent need for coordinated action in the La Plata Basin, where these fish face similar threats from dams, altered water flows, and intensive fishing pressure.
Together, these initiatives represent some of the most ambitious international efforts to protect migratory freshwater fish, reinforcing the central principle of CMS: that effective conservation solutions must encompass the full geographic range of migratory species and depend fundamentally on cooperation between countries.
Broader Implications: Ecosystems, Economies, and Livelihoods
The implications of this freshwater biodiversity crisis extend far beyond the fish themselves.
- Economic Vitality and Food Security: The decline of migratory freshwater fish directly threatens the food security and livelihoods of hundreds of millions of people globally, particularly in developing nations where inland fisheries are a primary source of protein and income. The economic impact of losing these valuable fisheries, including associated processing, trade, and tourism, could be catastrophic.
- Ecological Web Disruptions: Migratory fish play crucial roles in riverine ecosystems. They act as vectors for nutrient transport between different habitats, help control insect populations, and serve as a vital food source for numerous other species, including birds, mammals, and other fish. Their disappearance can lead to cascading effects throughout the food web, disrupting the delicate balance of aquatic and riparian ecosystems. The health of rivers as dynamic, living systems is intrinsically linked to the presence and movement of these species.
Expert Voices Emphasize Urgency
The urgency of the situation was powerfully articulated by leading experts involved in the report.
Dr. Zeb Hogan, the lead author of the assessment, stressed the hidden nature of these 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." His statement underscores the need for greater public awareness and political will to address this often-unseen crisis.
Amy Fraenkel, CMS Executive Secretary, highlighted the strategic importance of the report: "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." Her remarks point to the critical nexus between scientific findings, policy formulation, and international collaboration.
Michele Thieme, Vice President and Deputy Lead of Freshwater at World Wildlife Fund-US, emphasized the transboundary nature of the challenge: "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." Her call for integrated basin-wide solutions reflects a fundamental shift in conservation philosophy, moving away from fragmented, localized efforts towards holistic, regional strategies.
Looking Ahead: A Blueprint for Recovery
The "Global Assessment of Migratory Freshwater Fishes" is more than just a warning; it is a blueprint for recovery. By comprehensively detailing the scale of the problem and outlining concrete steps for conservation, it provides a critical foundation for action. The ongoing COP15 in Brazil serves as a pivotal moment for international policymakers to translate these findings into tangible commitments and coordinated strategies. The fate of hundreds of migratory freshwater fish species, and by extension, the health of global river systems and the well-being of millions of people, hinges on the collective will to address this urgent and complex biodiversity crisis.
By the Numbers: A Snapshot of Decline
- 81%: Estimated global decline in migratory freshwater fish populations since 1970.
- 97%: Of the 58 CMS-listed migratory fish species (both freshwater and saltwater) now threatened with extinction.
- 325: Number of migratory freshwater fish species identified as candidates for international protection under CMS Appendices.
- ~15,000: Total freshwater fish species assessed by IUCN, forming the basis of the report’s extensive data.
- 11,000 km: Longest known freshwater migration, undertaken by the Dorado Catfish in the Amazon Basin.
- US$436 million: Estimated annual value of the Amazon’s migratory fish fisheries, crucial for regional economies.
- Hundreds of millions: People worldwide dependent on inland fisheries for food and livelihoods.
- One-third: Proportion of the world’s large rivers now fragmented by dams, hindering fish movement.
