The silent, powerful journeys of countless aquatic species, fundamental to the health of our planet’s freshwater ecosystems, are rapidly disintegrating. A groundbreaking report released by the Convention on the Conservation of Migratory Species of Wild Animals (CMS), a United Nations environmental treaty, paints a stark picture: many of the longest and most vital animal migrations on Earth, occurring beneath the surface of rivers, are now on the brink of collapse. The implications extend far beyond the aquatic realm, threatening food security, livelihoods, and the delicate balance of riverine environments that sustain millions of people worldwide.
A Biodiversity Crisis Beneath the Surface
The "Global Assessment of Migratory Freshwater Fishes," unveiled at the CMS 15th Meeting of the Conference of the Parties (COP15) in Brazil, has identified migratory freshwater fish as among the most imperiled species globally. These remarkable creatures, whose life cycles are intricately linked to the unimpeded flow of rivers, play a critical role in maintaining the ecological integrity of these vital waterways. They are essential for supporting robust inland fisheries, providing a crucial source of protein and income for hundreds of millions of people, particularly in developing nations.
The assessment, a culmination of extensive global data analysis and IUCN evaluations of nearly 15,000 freshwater fish species, reveals a deeply concerning trend: migratory freshwater fish populations have plummeted by an estimated 81% worldwide since 1970. This catastrophic decline underscores a largely overlooked biodiversity crisis. While attention has often been focused on terrestrial and marine species, the silent disappearance of migratory fish from our rivers represents an equally urgent environmental emergency.
Hundreds of Species Face Extinction Risk
The report highlights that hundreds of migratory fish species require coordinated international action for their survival. It provides compelling evidence that fish species dependent on connected river systems that transcend national borders are experiencing rapid population declines. The primary drivers of this crisis are multifaceted, stemming from human activities that fragment habitats, degrade water quality, and alter natural ecological processes.
Chief among these threats is the proliferation of dam construction. Dams, while often built for hydroelectric power, irrigation, or flood control, create insurmountable barriers for fish attempting to reach their ancestral spawning grounds or crucial feeding areas. This fragmentation of river systems severs vital life-line connections, isolating populations and preventing successful reproduction. Habitat fragmentation, driven by land-use changes, urbanization, and deforestation along riverbanks, further exacerbates the problem by reducing available resting, feeding, and breeding sites.
Pollution, from agricultural runoff carrying pesticides and fertilizers to industrial effluents and plastic waste, contaminates freshwater environments, directly harming fish and degrading their habitats. Overfishing, often exacerbated by unsustainable practices and weak regulatory frameworks, depletes fish stocks faster than they can replenish. Compounding these issues are climate-related ecosystem changes, including altered precipitation patterns leading to extreme floods and droughts, rising water temperatures, and shifts in water chemistry, all of which disrupt the delicate balance of freshwater ecosystems upon which these migratory species depend.
In total, the assessment has identified 325 migratory freshwater fish species as candidates for international conservation efforts, a significant expansion beyond the 24 species already listed under the Convention. These species are now considered to be at high risk without concerted global intervention. The report categorizes these candidates for listing under the Convention’s Appendices I (species requiring the strictest protection) and II (species needing international cooperation to ensure their conservation). This comprehensive list points to a pervasive biodiversity crisis unfolding across shared river systems worldwide.
Key River Systems at Critical Juncture
The report specifically identifies several critical river systems that are priorities for urgent conservation action. These include South America’s vast Amazon and La Plata-Paraná basins, Europe’s mighty Danube, Asia’s economically vital Mekong, Africa’s iconic Nile, and the Ganges-Brahmaputra system in the Indian subcontinent. These river systems, some of the most biologically diverse and economically important on the planet, are facing unprecedented pressure from human development and environmental degradation.
The Amazon Basin, a global stronghold for migratory freshwater fish, is under increasing threat from deforestation, mining, and agricultural expansion. Despite its immense size and ecological significance, development pressures are jeopardizing its status as a refuge for these species. A case study presented alongside the global assessment focused on the Amazon, identifying 20 migratory fish species that meet the criteria for potential listing under CMS Appendix II. These species are central to regional fisheries, contributing approximately 93% of total fish landings and supporting an industry valued at an estimated US$436 million annually.
One of the most striking examples highlighted is the dorado (gilded) catfish (Brachyplatystoma rousseauxii). This bottom-dwelling species, recognizable by its metallic gold/silver coloration and substantial size (reaching up to 2 meters or 6.5 feet), undertakes the longest known freshwater migration of any fish. Its life cycle involves an extraordinary 11,000-kilometer journey from the Andean headwaters to coastal nursery areas, a testament to the incredible resilience and adaptability of these creatures, and the vast, interconnected river systems they depend upon.
Recommendations for Coordinated Global Action
The report not only details the severity of the crisis but also outlines practical, actionable steps that governments can implement immediately to halt and reverse these declines. These recommendations emphasize the need for a paradigm shift in how river systems are managed, moving from a fragmented, nationalistic approach to one that recognizes rivers as interconnected ecosystems that transcend political boundaries.
Key proposed actions include:
- Restoring and protecting river connectivity: This involves implementing measures to ensure fish passage, such as building fish ladders or removing obsolete dams, and maintaining natural flow regimes.
- Reducing pollution: Stricter regulations on industrial and agricultural discharge, coupled with improved wastewater treatment, are crucial to improving water quality.
- Combating overfishing: Implementing sustainable fishing quotas, enforcing regulations against destructive fishing practices, and promoting responsible aquaculture are essential.
- Addressing climate change impacts: Developing climate adaptation strategies for freshwater ecosystems and mitigating greenhouse gas emissions are critical for long-term survival.
- Enhancing international cooperation: Establishing and strengthening transboundary river basin management agreements and collaborative conservation initiatives are paramount for species that migrate across national borders.
A Largely Overlooked Freshwater Biodiversity Crisis
The decline of animals in freshwater ecosystems is occurring at a rate faster than in terrestrial or oceanic environments. However, the collapse of migratory freshwater fish populations has received disproportionately little global attention. These fish rely on vast, uninterrupted river pathways that connect their spawning grounds, feeding areas, and floodplain nurseries, often spanning multiple countries. When these vital connections are disrupted by the construction of dams, altered water flows, or habitat degradation, populations can collapse with alarming speed.
The scale of the problem is staggering. The report estimates that nearly all (97%) of the 58 CMS-listed migratory fish species (encompassing both freshwater and saltwater species) are now threatened with extinction. The findings underscore that hundreds of migratory freshwater fish species are in a precarious conservation status, demanding immediate and decisive action. Protecting these species requires a fundamental shift in management practices, treating rivers as integrated systems rather than a series of separate national waterways.
Amazon Basin and La Plata Initiatives: A Glimpse of Hope
As the host nation for COP15, Brazil has taken a proactive stance by proposing several conservation measures focused on the critically important South American river systems: the Amazon and the La Plata-Paraná. These initiatives aim to address the specific threats facing migratory fish in these regions and serve as a model for international cooperation.
In recognition of the urgent needs in the Amazon, Brazil and other regional partners are developing a Multi-species Action Plan for Amazonian Migratory Catfish, slated for implementation between 2026 and 2036. This plan, a product of regional collaboration, seeks to safeguard these iconic species and their vital habitats.
Furthermore, Brazil has put forth a proposal to add the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II. This proposal highlights the pressing need for coordinated action within the La Plata Basin, where these fish are facing significant threats from dams, altered water flows, and intense fishing pressure. The inclusion of this species would facilitate enhanced international cooperation and resource allocation for its conservation.
These proposed actions represent some of the most ambitious international efforts to date aimed at protecting migratory freshwater fish. They embody the core principle of the CMS: conservation solutions must encompass the entire geographic range of migratory species and depend on robust collaboration between nations.
Expert Voices: A Call for Unified Action
The urgency of the situation has been echoed by leading experts in the field. Dr. Zeb Hogan, the lead author of the report, emphasized the critical need for international cooperation: "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, CMS Executive Secretary, highlighted the report’s significance in bringing a critical 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, underscored the transboundary nature of the crisis: "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 Stark Numbers of Global Migratory Fish Decline
The report presents a sobering quantitative overview of the crisis:
- 81% decline: Migratory freshwater fish populations have declined by approximately 81% worldwide since 1970.
- 97% threatened: Nearly all (97%) of the 58 CMS-listed migratory fish species (freshwater and saltwater) are now threatened with extinction.
- 325 species candidates: An additional 325 migratory freshwater fish species have been identified as candidates for international conservation listing.
These statistics serve as a stark reminder of the profound impact human activities have had on freshwater ecosystems and the urgent need for global, coordinated efforts to preserve these invaluable natural resources and the species that depend on them. The future of these ancient migrations, and the health of the rivers they traverse, now rests on the collective will of the international community to act decisively.
