For most migratory species, movement is not optional. This is how they survive
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Hidden beneath the surface of large rivers around the world, some of the largest animal movements on Earth take place – migrations that rival, in terms of biomass, the famous movements of herds of zebras and wildebeests across the Serengeti desert in Africa.
For centuries, fish migrations were as predictable as the seasons. Salmon, sturgeon, giant catfish and many other species roamed the rivers in large numbers, guided by rising water levels, flood pulses and biological signs of their evolution.
These species are extraordinarily diverse, ranging from beluga sturgeon – an enormous fish that can live for more than a century and produces the world’s most prized caviar – to giant river carp, tropical eels, gold-spotted shad and goliath catfish, all of which travel to survive, in some cases hundreds or even thousands of kilometers.
Your journeys can cross continents. But the fish and their great migrations are disappearing.
For most migratory fish, movement is not optional. This is how they survive. When dams block routes, when fishing intensifies at migratory chokepoints, and when floodplains and spawning areas are isolated or degraded, most migratory fish don’t simply go elsewhere. They can’t. First, migration slows, then fluctuates. In some rivers, especially those blocked by dams, it disappears completely.
A new one for the March 2026 international meeting of the parties to the Convention on the Conservation of Migratory Species of Wild Animals provides the clearest picture yet of this decline — and what is needed to stop it.
More than 15,000 species of freshwater fish were analyzed, identifying which ones migrate and assessing their conservation status or risk of extinction. We then focused on migratory species with declining populations and identified those where countries will have to work together to help them recover and thrive. The results are worrying.
They identified 325 species of migratory freshwater fish as candidates for coordinated international conservation actions under the . Many of the largest species, the giants that make the longest and most dramatic journeys, are the ones most endangered. Among the migratory fish already listed in the Convention on Migratory Species, 97% are at risk of extinction. In Asia, populations of migratory freshwater megafish have declined by more than 95% since 1970.
The Mekong’s endangered giants
Over the last 25 years, the largest freshwater fish in the world have been studied.
One of these extraordinary animals, the Mekong giant catfish, weighs more than 295 kg. It has migrated hundreds of kilometers along the Mekong River, sustaining fishing and cultural traditions throughout the region. Today, it is critically endangered because dams are blocking its route to spawning areas and overfishing at migration chokepoints is killing the large adults on which the population depends.
In Cambodia, small migratory fish known as trey riel They are so important that they gave their name to the national currency. In South Asia, a migratory fish from the shad family, the hilsa, is so culturally important that it is sometimes given as a wedding gift, wrapped in ornate fabric and adorned with flowers.
The migrations of these fish, like the migrations of buffalo across the American plains in the past, shape ecosystems, livelihoods, and culture. In the Mekong Basin alone, fisheries produce more than 2 million metric tons of food each year, helping to feed tens of millions of people. When these fish disappear, people suffer.
Long migrations under threat
Declines are also occurring in other large river systems.
In the Amazon, some of the largest catfish on the planet migrate across much of the continent. Sea bream can reach 2 meters in length and complete a migration of more than 10,000 kilometers between Andean springs and coastal nurseries, the longest freshwater fish migration ever recorded.
At the Teotônio rapids between Bolivia and Brazil, fishermen used to hang from wooden scaffolding above the turbulent waters to throw their spears at the bream as they moved upstream — until the rapids were flooded by new dams. Changes in river flow, dams and overfishing are increasingly disrupting these journeys, and seabream populations in the upper reaches of the river in Bolivia have plummeted.
Across the Northern Hemisphere, migratory fish such as salmon, sturgeon and shad have suffered significant losses as rivers have been dammed and polluted, while many populations have been heavily overfished.
In the Columbia River basin, dam construction transformed an immense river system into a series of dams and reservoirs and prevented fish from accessing much of their historic range.
In South Asia, fish like mahseero goonch and the greet They are also in decline due to pressure from dams, overfishing, sand extraction, pollution and habitat loss, even as they continue to be fundamental to fisheries and riverine cultures in the Ganges, Brahmaputra and Indus river basins.
Why Migratory Fish Are Facing Difficulties
Migratory freshwater fish depend on long, interconnected river corridors, often crossing multiple countries. Dams, habitat fragmentation, pollution, overfishing and climate change are disrupting these connections. Once routes are cut off, populations can quickly collapse.
Esee is an increasingly international problem. More than 250 rivers and lakes around the world cross national borders, and about 47% of the Earth’s land surface is located in shared river basins. But freshwater fish are still too often managed at a local or national level, as if rivers and fish movements stop at political boundaries.
This is why international agreements are important. It is the only global treaty specifically designed to encourage countries to work together to conserve migratory animals.
For freshwater fish, cooperation can start with something as simple as sharing data between countries, and can extend to coordinated actions to reduce overfishing, protect floodplains and spawning areas, and keep rivers connected. The most fundamental solution is to manage rivers as connected ecological systems rather than isolated national waterways.
Of these, many could be considered for inclusion on the convention list. Listing does not automatically save a fish, but it does provide a mechanism to allow countries to coordinate monitoring, management and conservation across borders. This is important because freshwater fish remain underrepresented in international conservation policy despite the magnitude of their decline.
We found that the river basins where international cooperation is now most urgently needed include the Amazon and La Plata-Paraná in South America, the Danube in Europe, the Mekong in Asia, the Nile in Africa and the Ganges-Brahmaputra in South Asia.
How to Bring Back Migratory Fish
Restoring migratory fish populations means maintaining healthy, free-flowing rivers, reconnecting rivers fragmented by dams and canals, improving fisheries management, protecting floodplains and wetlands, and restoring habitats that have been drained, deforested, or isolated by development.
There are examples of success. In the US state of Washington, the removal of dams on the Elwha and White Salmon rivers has reopened habitats that were inaccessible to migratory fish about a century ago, allowing the return of Chinook salmon, coho salmon, steelhead and lamprey.
The world’s great fish migrations have not disappeared everywhere, but they are declining. This new assessment offers a clearer picture of where international cooperation is most urgently needed. It is up to humanity to protect these extraordinary aquatic animals, which support millions of people, enrich their lives and make the world a more wonderful place.
Zeb Hogan is a professor of biology at the University of Nevada.
This text was published originally by at 10:13 am on March 25, 2026 and adapted for publication by Poder360.
