The world’s rivers are witnessing a silent crisis, with some of the planet’s most significant species migrations rapidly collapsing, according to a comprehensive new assessment by the UN Convention on the Conservation of Migratory Species of Wild Animals (CMS). The report, titled The Global Assessment of Migratory Freshwater Fishes, launched at the CMS COP15 in Brazil, paints a dire picture of migratory freshwater fish populations, highlighting their critical role in maintaining river health, supporting vast inland fisheries, and sustaining hundreds of millions of people worldwide. These vital aquatic inhabitants are now classified among the most imperiled wildlife on Earth.
A Hidden Catastrophe Unveiled
The assessment meticulously identifies 325 migratory freshwater fish species that warrant coordinated international conservation efforts. This highlights a largely overlooked biodiversity crisis unfolding across the globe’s interconnected river basins. These species are experiencing accelerating declines, driven by a confluence of human-induced pressures, including extensive dam construction, habitat fragmentation, pervasive pollution, unsustainable fishing practices, and the far-reaching impacts of climate change on aquatic ecosystems.
Dr. Zeb Hogan, lead author of the assessment, underscored the gravity of the situation: "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 emphasizes the urgent need for collaborative, transboundary conservation strategies.
Data Reveals Stark Declines
The findings are particularly alarming when viewed against existing data. Migratory freshwater fish populations have experienced a staggering decline of approximately 81% since 1970. This precipitous drop far exceeds the declines observed in many terrestrial and marine species, yet has received significantly less international attention. The report further reveals that nearly all (97%) of the 58 CMS-listed migratory fish species, encompassing both freshwater and saltwater species, are now threatened with extinction. The new assessment deepens this understanding by identifying hundreds of migratory freshwater fish with an unfavorable conservation status, emphasizing that effective protection necessitates managing rivers as unified, connected systems rather than as isolated national waterways.
Coenraad Krijger, CEO of Wetlands International, articulated the urgency: "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 commitment from a prominent conservation organization signals a growing recognition of the crisis and a proactive approach to addressing it.
The Importance of Migratory Freshwater Fish
Migratory freshwater fish are integral to the health and functioning of aquatic ecosystems. They connect different parts of rivers, from spawning grounds to feeding areas and nursery habitats, often traversing vast distances that span multiple countries. Their migrations play a crucial role in nutrient cycling, seed dispersal, and maintaining the ecological balance of river systems. Furthermore, these fish form the backbone of many significant inland fisheries, providing a vital source of protein and income for hundreds of millions of people, particularly in developing nations. The collapse of these populations therefore has profound ecological, economic, and social implications.
Drivers of the Crisis: A Multifaceted Threat
The report identifies several key drivers behind the alarming decline of migratory freshwater fish:
- Dam Construction and Habitat Fragmentation: The proliferation of dams, weirs, and other artificial barriers across rivers has severely disrupted natural migratory pathways. These structures impede fish movement, isolate populations, alter water flow regimes, and can lead to significant habitat loss downstream. The cumulative impact of these barriers across major river systems is a primary contributor to population declines.
- Pollution: Agricultural runoff, industrial discharge, and untreated sewage introduce a cocktail of pollutants into rivers, degrading water quality and harming fish health. Pesticides, heavy metals, and excess nutrients can impair fish reproduction, growth, and survival, particularly for species with sensitive life stages.
- Overfishing: While many migratory fish are prized for commercial and subsistence fishing, unsustainable harvesting practices, including illegal and unregulated fishing, have depleted stocks in many regions. Combined with declining population numbers, overfishing can push species towards the brink of extinction.
- Climate Change: Shifting rainfall patterns, increased water temperatures, and more frequent extreme weather events, such as droughts and floods, are altering freshwater ecosystems. These changes can disrupt spawning cues, reduce habitat availability, and exacerbate the impacts of other stressors.
Global Efforts and Regional Spotlights
The CMS COP15, hosted in Brazil, provided a crucial platform for the launch of the assessment and for the discussion of immediate conservation actions. Brazil, a nation with some of the world’s most significant river systems, has put forward several ambitious conservation proposals.
Spotlight on South America’s Great Rivers
Brazil is focusing on two of South America’s most vital river systems: the Amazon and the La Plata-Paraná. The Amazon Basin, renowned as a last great stronghold for migratory freshwater fish, faces increasing 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). This large, bottom-dwelling catfish, recognizable by its metallic gold/silver skin and impressive size (reaching up to 2 meters or 6.5 feet), is highly valued in commercial fisheries. It undertakes a remarkable migration spanning 11,000 kilometers, from the Andean headwaters to coastal nursery grounds, representing one of the longest known freshwater fish migrations. To bolster its protection, Brazil and other regional governments are proposing a Multi-species Action Plan for Amazonian Migratory Catfish (2026-2036), developed through collaborative regional efforts.
In the La Plata Basin, Brazil has also proposed adding the spotted sorubim catfish (Pseudoplatystoma corruscans) to CMS Appendix II. This proposal underscores the urgent need for coordinated action to address threats posed by dams, altered water flows, and fishing pressures in this critical basin. These initiatives represent some of the most significant international efforts to date aimed at safeguarding migratory freshwater fish species, reinforcing the core principle of CMS: conservation solutions must encompass the entire range of migratory species and depend on international cooperation.
Tools for Immediate Action
The new assessment not only diagnoses the problem but also outlines practical tools that governments can implement immediately to bolster conservation efforts. While specific tools were not detailed in the initial release, the implication is a focus on policy, management, and practical interventions that can be scaled up across national borders. These could include measures such as:
- Establishing and enforcing protected areas: Designating critical habitats and migratory corridors as protected zones to limit destructive activities.
- Improving dam management: Implementing fish passage solutions and adjusting dam operations to minimize ecological impacts.
- Reducing pollution: Strengthening regulations and promoting sustainable practices in agriculture and industry.
- Combating illegal fishing: Enhancing monitoring, surveillance, and enforcement to prevent overexploitation.
- Restoring degraded habitats: Undertaking projects to reconnect rivers, restore floodplains, and improve water quality.
- International cooperation and data sharing: Fostering collaboration between nations to manage shared river systems and migratory species effectively.
Broader Implications and the Path Forward
The crisis facing migratory freshwater fish has far-reaching implications beyond the ecological realm. The decline of these species threatens food security for millions, impacts local economies dependent on fisheries, and diminishes the intrinsic value of biodiversity. Michele Thieme, Vice President and Deputy Lead of Freshwater at WWF-US, highlighted the interconnectedness: "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 serves as a critical wake-up call, emphasizing that the health of our planet’s freshwater ecosystems is inextricably linked to the survival of migratory fish. The coordinated efforts proposed and initiated at COP15, particularly those concerning South America’s vital river systems, offer a hopeful glimpse into what can be achieved when nations unite behind a common conservation goal. However, the scale of the challenge demands sustained political will, increased investment, and a fundamental shift in how humanity manages its freshwater resources. The future of these remarkable migrations, and the health of the rivers they inhabit, hinges on immediate and decisive action.
