Amazon's Longest Migration Under Threat

The dorado catfish undertakes the longest freshwater migration on Earth, a 7,000-mile round trip within the Amazon River system.

This migration is currently facing severe endangerment. Recent scientific findings detail the dorado's life cycle: it spawns in the Andean headwaters of the Amazon River, its larvae drift downstream to the Atlantic estuary where they mature, and then the adult fish return to the Andes to reproduce. However, this ancient migratory route is compromised by hydropower dams and river fragmentation, which obstruct the fish's access to breeding grounds and contribute to significant population decreases.

In response, Brazil proposed an international action plan at the UN-backed Convention for the Conservation of Migratory Species (CMS), which was signed recently. This plan aims to connect the river system and protect the dorado, along with six other species of migratory Goliath catfish, involving six South American countries in the effort.

The Vital Role of Migratory Catfish

Dr. Zeb Hogan, a biology professor at the University of Nevada and freshwater fish councilor for CMS, stated the dorado is vital for Amazon River communities and emphasized the need for collaborative protection efforts.

Protecting migratory species presents challenges due to their international movements; the dorado, for instance, inhabits areas across nine South American countries. Actions in one river section impact the entire system; studies in 2019 indicated an 80% reduction in dorado numbers in Bolivia over 15 years, following the construction of two dams downstream in Brazil.

The dorado functions as an apex predator, regulating populations of smaller species and maintaining the river ecosystem's balance. Hogan suggests that improved planning for future hydropower projects, including early assessments of their impact on migratory fish, could mitigate harm. For existing dams, interventions such as fish ladders or the removal of old structures could restore migration routes, potentially leading to rapid fish recovery.

Economic and Cultural Lifelines

Migratory fish are crucial for local food security, economies, and cultural heritage. Dino Delgado, engagement and policy lead for Wildlife Conservation Society (WCS) and Amazon Waters, noted the high value of species like dourada and piramutaba for their size and food quality.

The Amazon region, home to approximately 47 million people, has fisheries heavily dependent on migratory species, which constitute 93% of the catch and generate $436 million annually.

Around 400 Indigenous groups in the Amazon rely on fishing for sustenance. Fishers from the Madeira basin, an area significantly affected by dams, have called for coordinated and urgent governmental action, stressing that international efforts must involve artisanal fishers, Indigenous peoples, and local communities.

Beyond hydropower, Amazonian fish populations also face threats from mercury contamination due to mining and from overfishing.

A New Action Plan for the Amazon

Delgado stated that with the action plan approved, initial work will focus on compiling local scientific and Indigenous knowledge about critical habitats and standardizing data collection regionally.

Guillermo Estupiñán, wetlands and aquatic resources specialist at WCS Brazil, described the collaboration among six Amazonian nations as a 'milestone' for biodiversity conservation, expected to enhance scientific knowledge and align policies and regulations across the region.

The dorado and laulau 'Goliath' catfish were added to the CMS protection list in 2024, which facilitated the development of the recently approved action plan. Amy Fraenkel, CMS Executive Secretary, highlighted this as a novel and powerful model for freshwater fish protection, building on successful cooperative agreements for other species.

A Global Crisis, A Local Model

The challenges faced by the dorado reflect a broader global crisis. A recent CMS report, analyzing 15,000 species, identified 325 migratory freshwater fish requiring international protection. Asia, with 205 listed species, was noted as a region with collapsing migrations, particularly in the Mekong Delta, home to the Mekong giant catfish. Hogan compared the scale of these underwater migrations to the Serengeti's land migrations. He also noted that none of the Lower Mekong nations are party to the treaty, representing a future opportunity.

Globally, migratory freshwater fish populations have decreased by 81% since 1970.

Fish are often primarily considered a food source rather than a biodiversity concern. Additionally, rivers, despite covering 47% of Earth's land as transboundary water, are frequently managed as local resources. The UN reports that approximately 70% of member states sharing waterways lack comprehensive cooperative management agreements, leaving aquatic life vulnerable.

Michele Thieme, vice president and deputy lead of freshwater for WWF-US, stated that rivers require integrated management, cross-border coordination, and investments in basin-wide solutions to prevent further loss of migrations.

The Amazon Basin, home to over 2,700 freshwater fish species, has 20 migratory fish meeting CMS protection criteria. Despite significant declines, Hogan views the 325 identified species as opportunities for collaboration, expressing cautious optimism that the Amazon's catfish action plan provides a replicable model for other nations to follow.