The world’s most remarkable and vital underwater migrations are facing an unprecedented collapse, according to a groundbreaking new assessment by the UN Convention on the Conservation of Migratory Species of Wild Animals (CMS). Launched at the CMS COP15 in Brazil, "The Global Assessment of Migratory Freshwater Fishes" paints a stark picture of these essential species, which are not only critical indicators of river health but also underpin vital global fisheries and sustain hundreds of millions of people. The report unequivocally states that migratory freshwater fish are among the most imperiled wildlife groups on the planet, with populations plummeting at an alarming rate.
A Silent Catastrophe Unfolding in Our Rivers
The assessment identifies a staggering 325 migratory freshwater fish species that are candidates for coordinated international conservation efforts. This highlights a biodiversity crisis that has largely been overlooked, unfolding silently within the world’s shared river basins. These species are under accelerating pressure from a confluence of human-induced threats, including the pervasive construction of dams that fragment river systems, widespread habitat degradation, escalating pollution from agricultural and industrial sources, unsustainable fishing practices, and the increasingly disruptive impacts of climate change on aquatic ecosystems.
Dr. Zeb Hogan, lead author of the assessment, emphasized the critical nature of the findings: "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 interconnectedness of river systems and the urgent need for transboundary cooperation.
The report’s findings are particularly alarming when considering the overall decline of freshwater fauna. Freshwater ecosystems, despite their vital role, are experiencing biodiversity loss at a faster rate than terrestrial and marine environments. Yet, the specific crisis facing migratory freshwater fish has received disproportionately little international attention. These species often rely on extensive, uninterrupted river corridors to complete their life cycles, connecting crucial spawning grounds, feeding areas, and nursery habitats, frequently spanning multiple national borders. The interruption of these essential pathways by infrastructure like dams, altered flow regimes, or habitat destruction can lead to rapid and devastating population declines.
An Alarming Decline: The Numbers Speak Volumes
The scale of the crisis is quantified in the report by startling statistics. Migratory freshwater fish populations worldwide have experienced a dramatic decline of approximately 81% since 1970. This figure is particularly sobering when compared to other wildlife groups. Furthermore, nearly all (97%) of the 58 migratory fish species already listed under CMS, encompassing both freshwater and saltwater species, are now threatened with extinction. The new assessment significantly expands this understanding by identifying hundreds of additional migratory freshwater fish species with unfavorable conservation statuses, reinforcing the urgent need for comprehensive management strategies that treat rivers as interconnected systems rather than isolated national waterways.
Coenraad Krijger, CEO of Wetlands International, voiced his grave concern: "Migratory freshwater fish populations are in freefall: crashing around 81% since 1970. We need to accelerate efforts to safeguard their Swimways and invest in the conservation of these species, which are critical to communities and ecosystems across the globe. This is why migratory fishes are one of the priorities in Wetlands International’s new 10-year strategy." This sentiment reflects a growing recognition within conservation organizations of the pivotal role these fish play and the urgent need for dedicated action.
The Role of Dams: A Major Obstacle to Migration
A significant driver of this decline is the proliferation of dams. While dams are often constructed for hydropower, irrigation, and flood control, they act as formidable barriers to migratory fish. These structures disrupt natural river flows, alter water temperatures, trap sediment essential for downstream habitats, and physically impede the movement of fish between different parts of their life cycle. The fragmentation of rivers by dams effectively breaks the "swimways" that these species have navigated for millennia.
The report implicitly calls for a re-evaluation of dam construction and management practices, advocating for the implementation of fish-friendly infrastructure, dam removal where feasible, and improved management of existing dams to allow for unimpeded fish passage. The economic and ecological costs of ignoring these migratory pathways are becoming increasingly apparent.
Spotlight on South America: A Vital Haven Under Threat
The COP15 summit, hosted in Brazil, provided a crucial platform for discussions and proposals aimed at bolstering the conservation of migratory freshwater fish, particularly in South America’s vast and ecologically rich river systems. Brazil, home to the Amazon and La Plata-Paraná basins, is at the forefront of these efforts.
The Amazon Basin, renowned as one of the last great strongholds for migratory freshwater fish, faces intensifying development pressures that threaten its unique biodiversity. The region is home to species undertaking some of the longest freshwater migrations on record. A prime example is the dorado catfish (Brachyplatystoma rousseauxii), a large, bottom-dwelling species recognized for its striking appearance and impressive size, reaching up to two meters in length. This species undertakes an extraordinary migration of up to 11,000 kilometers, traveling from their spawning grounds in the Andean headwaters to coastal nursery areas. This remarkable journey, representing one of the longest recorded freshwater fish migrations, highlights the immense distances these species cover and their dependence on intact riverine networks.
In recognition of this critical situation, Brazil and other nations are championing a Multi-species Action Plan for Amazonian Migratory Catfish (2026-2036). This plan, developed through extensive regional cooperation involving multiple countries, aims to coordinate conservation efforts across the Amazon basin, addressing the shared challenges faced by these iconic species.
Furthermore, Brazil has proposed the inclusion of the spotted sorubim catfish (Pseudoplatystoma corruscans) in CMS Appendix II. This proposal underscores the urgent need for coordinated action within the La Plata Basin, where this species is severely threatened by dam construction, altered river flows, and intense fishing pressures.
These ambitious initiatives represent some of the most significant international efforts to date to safeguard migratory freshwater fish species. They embody the core mission of CMS: that conservation solutions for migratory species must transcend national boundaries and necessitate robust international cooperation to achieve success.
A Call for Coordinated Action and Basin-Wide Solutions
The implications of this report extend far beyond the immediate threat to fish populations. Migratory freshwater fish play a crucial role in maintaining the health and functioning of river ecosystems. They help to distribute nutrients, control populations of other aquatic organisms, and serve as an important food source for both wildlife and human communities. The collapse of these populations can trigger cascading effects throughout the ecosystem, leading to reduced biodiversity, diminished ecosystem services, and significant impacts on the livelihoods of communities that depend on healthy fisheries.
Michele Thieme, Vice President and Deputy Lead of Freshwater at WWF-US, articulated the urgency: "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."
The assessment provides governments with practical tools that can be deployed immediately to address the crisis. These likely include measures such as:
- Improving Fish Passage: Implementing and upgrading infrastructure like fish ladders and bypass channels at dams to allow fish to migrate upstream and downstream.
- Restoring Habitat Connectivity: Removing unnecessary barriers, restoring natural river flows, and protecting riparian zones to ensure unimpeded access to spawning and feeding grounds.
- Reducing Pollution: Implementing stricter regulations and enforcement to curb industrial, agricultural, and urban pollution that degrades water quality.
- Sustainable Fisheries Management: Implementing quotas, gear restrictions, and seasonal closures to prevent overfishing and ensure the long-term viability of fish populations.
- Addressing Climate Change Impacts: Developing strategies to mitigate the effects of altered precipitation patterns, increased water temperatures, and extreme weather events on freshwater ecosystems.
- Strengthening International Cooperation: Fostering collaborative agreements and action plans for shared river basins to ensure coordinated conservation efforts across national borders.
The report’s release at COP15 in Brazil, a nation grappling with the immense ecological significance and development pressures of its river systems, underscores the global relevance of the findings. The proposed actions for the Amazon and La Plata basins serve as a potential blueprint for other regions facing similar challenges.
In conclusion, "The Global Assessment of Migratory Freshwater Fishes" serves as a critical wake-up call. It highlights a hidden environmental crisis with profound implications for biodiversity, ecosystem health, and human well-being. The report’s call for urgent, coordinated, and basin-wide action is not merely a recommendation but an imperative if we are to preserve these vital underwater migrations and the health of the rivers that sustain them for future generations. The time for robust international collaboration and significant investment in freshwater ecosystem conservation is now, before these irreplaceable natural wonders are lost forever.