A groundbreaking new report from the Convention on the Conservation of Migratory Species of Wild Animals (CMS), a pivotal United Nations environmental treaty, has issued a stark warning: many of the Earth’s longest and most vital animal migrations, particularly those occurring beneath the surface of rivers, are now experiencing a rapid and alarming breakdown. This critical assessment underscores a largely overlooked biodiversity crisis unfolding in the world’s freshwater ecosystems, threatening not only the species themselves but also the health of rivers and the livelihoods of hundreds of millions of people globally.
The comprehensive "Global Assessment of Migratory Freshwater Fishes," unveiled at the CMS 15th Meeting of the Conference of the Parties (COP15) hosted in Brazil, paints a grim picture. It identifies migratory freshwater fish as among the most imperiled species worldwide. These fish are not merely components of aquatic ecosystems; they are foundational to their health, serving as keystone species that transport nutrients, regulate food webs, and maintain ecological balance. Furthermore, they underpin major inland fisheries, providing essential protein and economic stability for communities across continents. The report’s findings necessitate an urgent re-evaluation of conservation priorities and a dramatic escalation of international collaborative efforts.
An Unseen Crisis: The Scale of Decline in Freshwater Migrations
While terrestrial and marine biodiversity loss often capture headlines, the plight of freshwater species, particularly migratory fish, has largely remained in the shadows. The assessment reveals that animals inhabiting freshwater ecosystems are experiencing declines at a rate significantly faster than their terrestrial or marine counterparts. For migratory freshwater fish specifically, the statistics are dire: populations have plummeted by an estimated 81% globally since 1970. This catastrophic drop is emblematic of a wider ecological unraveling in river systems worldwide. Alarmingly, nearly all (97%) of the 58 migratory fish species currently listed under CMS (which includes both freshwater and saltwater species) are now classified as threatened with extinction.
These fish species rely intrinsically on long, uninterrupted river pathways that serve as vital conduits, linking disparate but essential habitats such such as spawning grounds, feeding areas, and floodplain nurseries. These journeys often span thousands of kilometers and traverse multiple national borders. The integrity of these pathways is paramount, and their disruption, whether through the construction of dams, alteration of natural water flows, or widespread habitat degradation, precipitates rapid and often irreversible population collapses. The report emphasizes that this crisis represents a profound and underappreciated threat to global biodiversity and the essential ecosystem services that healthy rivers provide.
Understanding the Convention on Migratory Species (CMS)
The Convention on the Conservation of Migratory Species of Wild Animals, also known as the Bonn Convention, is an environmental treaty under the aegis of the United Nations Environment Programme (UNEP). Established in 1979 and entering into force in 1983, CMS aims to conserve migratory species and their habitats globally. It provides a framework for signatory nations to cooperate in the conservation of species that migrate across international boundaries, recognizing that effective conservation for these species requires a concerted, transboundary approach. The convention operates through two appendices: Appendix I lists migratory species that are endangered and require strict protection, while Appendix II lists migratory species that have an unfavorable conservation status and would benefit significantly from international cooperative agreements. The latest assessment by CMS underscores the treaty’s evolving role and the pressing need to extend its protective scope to species that have historically received less attention.
The Global Assessment: A Call for Coordinated International Action
The "Global Assessment of Migratory Freshwater Fishes" is the most comprehensive overview to date of the conservation challenges confronting these species. It synthesizes extensive global datasets and draws upon IUCN (International Union for Conservation of Nature) assessments of nearly 15,000 freshwater fish species. This robust scientific foundation provides undeniable evidence that fish dependent on connected rivers across national borders are declining at an alarming rate.
The primary drivers of this rapid decline are multifaceted and interconnected:
- Dam Construction and Habitat Fragmentation: Dams are perhaps the most significant impediment, physically blocking migration routes, altering flow regimes, and transforming riverine habitats into static reservoirs. The proliferation of dams, particularly large hydropower projects, has severely fragmented river systems globally.
- Pollution: Industrial discharges, agricultural runoff, and untreated sewage contaminate freshwater ecosystems, impacting fish health, reproduction, and survival. Chemical pollutants can disrupt endocrine systems, reduce oxygen levels, and directly poison fish and their food sources.
- Overfishing: Unsustainable fishing practices, including illegal, unreported, and unregulated (IUU) fishing, exert immense pressure on fish populations, particularly those that aggregate during migrations, making them vulnerable to mass capture.
- Climate-Related Ecosystem Changes: Global warming is altering river temperatures, flow patterns, and water availability. Changes in precipitation regimes can lead to more extreme floods or droughts, disrupting crucial spawning cues and altering habitat suitability. The increasing frequency and intensity of heatwaves can push water temperatures beyond species’ tolerance limits.
In total, the assessment identifies a staggering 325 migratory freshwater fish species as prime candidates for international conservation efforts, in addition to the 24 already listed under CMS Appendices. This highlights a largely overlooked biodiversity crisis demanding immediate and concerted action across shared river systems. The priority river systems identified for urgent 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 river basins, home to incredible freshwater biodiversity, are also among the most threatened by human development and climate change.
A Regional Focus: The Amazon Basin and South American Initiatives
As the host of COP15, Brazil has taken a proactive stance, proposing several significant conservation measures centered on South America’s largest river systems: the Amazon and La Plata-Paraná. The Amazon Basin, renowned for its unparalleled biodiversity, remains one of the last major strongholds for migratory freshwater fish. However, this status is increasingly precarious due to escalating development pressures, including planned hydropower projects, deforestation, and expansion of agricultural frontiers.
A detailed case study accompanying the global assessment identified 20 migratory fish species within 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 fish landings and supporting an industry valued at an estimated US$436 million annually. The socio-economic implications of their decline are immense, directly impacting food security and the livelihoods of countless indigenous and local communities.
Among these remarkable species is the dorado (gilded) catfish (Brachyplatystoma rousseauxii). This bottom-dwelling species, characterized by its metallic gold/silver coloration and impressive size (reaching up to 2 meters or 6.5 ft), undertakes the longest known freshwater migration of any fish on Earth. Its complex life cycle involves an epic journey of up to 11,000 kilometers, from the Andean headwaters where it spawns, all the way to distant coastal nursery areas near the Amazon estuary, and back again. Such incredible feats of endurance underscore the critical need for an entire, connected river system to complete their life cycles.
To bolster conservation efforts for these vital species, Brazil and other regional countries are proposing a Multi-species Action Plan for Amazonian Migratory Catfish (2026-2036). This initiative, developed through extensive regional cooperation, aims to create a harmonized strategy for managing these shared resources. Brazil has also put forward a proposal to add the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II, highlighting the urgent need for coordinated action within the La Plata Basin, where these fish face similar threats from dam construction, altered water flows, and intense fishing pressure. These initiatives collectively represent some of the most ambitious international efforts to safeguard migratory freshwater fish, reinforcing the core principle of CMS: effective conservation solutions must encompass the full geographic range of migratory species and are inextricably linked to robust international cooperation.
Practical Steps for Governments and Broader Implications
The report outlines a series of practical, immediate steps that governments can take to reverse the trend of decline. These include:
- Restoring River Connectivity: Implementing dam removal projects where feasible, and installing effective fish passages (e.g., fish ladders, nature-like bypasses) at existing dams.
- Controlling Pollution: Strengthening regulations and enforcement to reduce industrial, agricultural, and urban pollution entering rivers. Investing in wastewater treatment infrastructure.
- Sustainable Fisheries Management: Implementing and enforcing quotas, closed seasons, and gear restrictions; combating IUU fishing; and empowering local communities in co-management efforts.
- Establishing Protected Areas: Designating and effectively managing protected areas that encompass critical migratory corridors and essential habitats.
- Integrating Climate Change Adaptation: Developing and implementing strategies to mitigate the impacts of climate change on freshwater ecosystems, such as restoring riparian vegetation for shade and maintaining environmental flows.
- Strengthening Transboundary Cooperation: Developing and implementing bilateral and multilateral agreements for shared river basins, ensuring coordinated management plans that recognize rivers as integrated ecological systems rather than fragmented national waterways.
The implications of this crisis extend far beyond the fish themselves. Ecologically, the loss of migratory fish can trigger trophic cascades, disrupting entire food webs and nutrient cycles. Many migratory species are vital for seed dispersal, sediment transport, and maintaining the health of floodplain ecosystems. Socially and economically, the collapse of these fisheries jeopardizes food security for millions, particularly in developing nations where river fish are a primary source of protein. It also threatens the cultural heritage and traditional practices of indigenous communities that have coexisted with and depended on these migrations for millennia. The economic impact on local economies, from direct fishing livelihoods to associated industries, is substantial.
Expert Voices and a Unified Call to Action
The urgency of the situation was underscored by leading experts. Dr. Zeb Hogan, the lead author of the report, articulated the fundamental truth: "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 highlights the interconnectedness of ecological health and human well-being.
Amy Fraenkel, CMS Executive Secretary, emphasized the historical oversight: "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 words are a call for political will to match the scientific understanding of the crisis.
Michele Thieme, Vice President and Deputy Lead of Freshwater at World Wildlife Fund-US, echoed the sentiment of urgency and the need for a paradigm shift in river management: "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 powerful statement serves as a stark reminder of the irreversible consequences of inaction.
The "Global Assessment of Migratory Freshwater Fishes" is more than just a report; it is a critical alarm bell. It serves as a scientific imperative for global leaders to recognize the hidden crisis beneath the water’s surface and to commit to the coordinated international action necessary to preserve these essential migrations, the health of our rivers, and the future of the communities that depend on them. The challenge is immense, but the opportunity to safeguard these vital species and ecosystems remains, provided action is taken swiftly and decisively.
