Freshwater migratory fish, known for undertaking vast and often spectacular journeys through rivers, lakes, and ponds, are facing a critical threat from a combination of human activities such as dam construction, pollution, and overfishing. These factors are increasingly preventing these fish from reaching their breeding grounds, putting numerous species at risk of severe population declines. In response to this growing concern, the United Nations has recently released a landmark report prioritizing the conservation of thirty flagship freshwater migratory fish species worldwide, highlighting the urgent need to protect these vital aquatic animals.
The report, produced by an international team of scientists, evaluated more than 15,000 species of freshwater migratory fish—representing approximately half of all fish species globally. Their findings were alarming: populations of these fish have plummeted by an estimated 81% over the past fifty years. This steep decline underscores the urgent need to shift conservation efforts toward these often-overlooked species, which play an essential role in sustaining human livelihoods around the world.
Dr. Zeb Hogan, a professor of biology at the University of Nevada, Reno and a co-author of the report, emphasized the significance of freshwater migratory fish not only for biodiversity but also for human society. “Freshwater fish support hundreds of millions of people globally,” he said, stressing that these fish are critical for food security. The report estimates that migratory freshwater fish provide sufficient sustenance for around 200 million people worldwide. Beyond their nutritional value, these fish are remarkably diverse, ranging from small species to giants weighing over 650 pounds (295 kilograms), capable of migrating astonishing distances exceeding 7,000 miles.
Examples of this diversity include the golden dorado, a visually striking predator that undertakes long-distance migrations in South America, and tropical eels that traverse thousands of miles across Oceania’s waterways. These migratory journeys are not only feats of endurance but also fundamental to the survival and reproduction of these species, enabling them to reach spawning grounds essential for their life cycles.
The United Nations first examined the status of freshwater migratory fish in 2011, but at that time, assessments covered only about 3,000 species. Since then, the International Union for Conservation of Nature (IUCN) has expanded data collection to include many more species. This latest report benefits from a much broader dataset, enabling scientists to provide a more comprehensive overview of the health and threats facing migratory fish around the world.
Among the thousands of species assessed, the UN identified 325 fish that urgently need to be included in a global agreement aimed at monitoring and supporting threatened migratory animals. From this group, a shortlist of 30 priority species was created. These fish are not only at risk but also hold significant cultural value for communities worldwide. Some of these species are native to the United Kingdom, including the Allis Shad, River Lamprey, Brook Lamprey, and Atlantic Salmon.
One particularly notable species on the list is the golden mahseer, often referred to as the “tiger of the river” in the Himalayan region. Michele Thieme, deputy lead for freshwater at World Wildlife Fund US and a contributor to the report, explained that the golden mahseer holds deep cultural and spiritual significance for people in its native range, far beyond its economic importance. However, like many other species on the list, it faces two principal threats: overfishing and habitat loss.
Habitat loss is often driven by dams and other river infrastructure that fragment river systems and alter their natural flow regimes. Such changes disrupt the ability of migratory fish to reach their spawning grounds, which can lead to population declines over time. Thieme highlighted how these barriers prevent fish from completing their life cycles, causing cascading ecological consequences.
In Europe, this problem is particularly acute, with migrating fish encountering an average of one barrier every kilometer (0.6 miles) along their routes. Many of these barriers are small structures such as culverts or weirs, which may no longer serve any useful purpose and could potentially be removed to restore connectivity. Dr. Janina Gray, head of science at the environmental charity WildFish, pointed out that while individual barriers might seem insignificant, their cumulative effect is devastating for migrating fish populations.
The energy fish expend trying to navigate these obstacles can drain their reserves, leaving them vulnerable to disease, predation, and forcing them to spawn in less suitable habitats. This not only reduces their reproductive success but also compromises the overall health of their populations.
Given that most migratory fish cross