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When annual rains return to the Amazon, murky rivers swell and speed up. For dolphin catfish, the rise and fall of the tide is a millennia-old signal that it’s time to make the voyage home across continents.
Their 7,000-mile round trip freshwater migration is the longest on Earth and one of the most endangered.
It was only in recent years that scientists revealed the full extent of the adventure. Dolphinfish, a member of the “Goliath” catfish family and also known as the golden catfish, spawn in the headwaters of the Amazon River in the Andes Mountains. The larvae flow thousands of miles downstream to the river’s mouth where it joins the Atlantic Ocean. Nutrient-rich brackish waters provide the perfect environment for young dolphinfish to feed and grow, reaching lengths of up to 6 feet and weights of 200 pounds. They then spend one to two years returning to the foothills of the Andes to lay their eggs and begin the cycle again.
But the same routes that dolphinfish have followed for thousands of years are now blocked by hydroelectric dams and river divides, preventing them from reaching their breeding grounds and causing a precipitous decline in their numbers.
A new international action plan proposed by Brazil and signed yesterday at the United Nations-backed Convention on Migratory Species (CMS) aims to reverse that trend, unite six countries to maintain river links, and give dolphinfish and six other migratory goliath catfish species a chance to complete their journey home.
“Dolphinfish are extremely important to the people who live along the Amazon River,” says Dr. Zeb Hogan, a University of Nevada biology professor and CMS Freshwater Fish Council member.
“We need to bring everyone together and work together to find ways to protect these amazing animals.”
Migratory birds are difficult to protect because they move across national borders. Dolphinfish live in nine countries in South America.
What happens in one part of a river has ripple effects throughout the system. A 2019 study found that dolphinfish numbers in Bolivia, one of the catfish spawning grounds, declined by 80% in the 15 years after two dams were built downstream from Brazil.
Dolphinfish are at risk of disappearing completely from the upper reaches of this river, but there are knock-on effects downstream as well. Dolphinfish are apex predators, keeping populations of small species in check and maintaining the overall balance of river ecosystems.
Hogan said more careful planning of future hydropower projects, including assessing impacts on migratory fish from the beginning, could help reduce damage and improve site selection.
In the case of existing dams, migratory routes can be unblocked through interventions such as fish ladders (structures or tunnels that allow migratory fish to bypass or pass through the dam), or the removal of old or disused dams. “Scientists are amazed at how quickly these migratory fish return when given a chance to move through the system,” Hogan says.
Migratory fish like dolphinfish are also vital to local food security, economies and cultural heritage.
“Species such as doulada, piramutaba, and other catfish are highly valued both for their size and the quality of their prey,” Dino Delgado, head of initiatives and policy for the Wildlife Conservation Society (WCS) and Amazon Waters, told CNN in a message.
The Amazon region is home to about 47 million people and its fisheries rely heavily on migratory fish, which account for 93% of the catch and generate $436 million annually, according to CMS.
In addition to hydroelectric dams, Amazon’s fish have been under pressure from mercury pollution from mining and overfishing.
In an open letter to the CMS delegation, fishermen from the Madeira Basin, one of the most fragmented areas of the Amazon River by the two large dams in Porto Velho, stressed the need for “coordinated and urgent action” by governments, adding that “international efforts will only succeed when working hand in hand with artisanal fishers, indigenous peoples and communities living in the Amazon.”
Delgado, who has worked closely on developing the action plan, said that once the plan is approved, important work will begin, from collating local scientific and Indigenous knowledge about critical habitats to regional efforts to standardize data collection.
The cooperation between the six Amazon countries is a “milestone” in biodiversity conservation that will strengthen scientific knowledge and harmonize policies and regulations across the region, Guillermo Estupiñán, wetland and aquatic resources expert at WCS Brazil, told CNN in an email.
Dolphinfish were added to the CMS protected list in 2024, along with the laulau “Goliath” catfish, which can grow up to 12 feet long and weigh 400 pounds. This laid the foundation for the currently approved action plan, said CMS Secretary Amy Frankel.
“We have cooperative agreements of this kind under CMS for other species,” Fraenkel said, pointing to efforts with Central Asian mammals as a successful model. “But we haven’t [previously] That’s why this example is so powerful because it was done on a freshwater fish. ”
The dolphinfish’s struggle reflects a global crisis. The CMS report, presented at the organization’s conference in Brazil last week, analyzed data on 15,000 species and identified 325 migratory freshwater fish species in need of international protection.
Asia, where 205 species are listed, has been cited as a hotspot for migratory collapse, particularly in the Mekong Delta region, where the 300 kg Mekong giant catfish, one of the world’s largest freshwater fish, migrates over hundreds of kilometers.
Hogan compares this migration to zebras and wildebeest crossing the Serengeti River in Tanzania. “The same amount of biological biomass is moving under the water, but we don’t know it because we can’t see it,” he says. But the Lower Mekong countries are not party to the treaty, a gap Hogan sees as a “long-term opportunity.”
Globally, migratory freshwater fish populations have declined by 81% since 1970. Fish are often overlooked in conservation because they are seen primarily as food rather than a “biodiversity issue,” Hogan said, adding that rivers are often managed as local resources, despite the fact that 47% of the Earth’s land area is covered by transboundary water. According to the United Nations, around 70% of UN member states that share waterways between two or more countries lack comprehensive cooperative agreements to manage them, leaving aquatic life subject to inconsistent protection.
“Rivers do not recognize borders, and neither do the fish that depend on them,” Michelle Thiem, WWF-US vice president and deputy head of freshwater, said in a press statement. “Rivers need to be managed as connected systems, coordinating across borders and investing in basin-wide solutions now, before these movements are lost forever.”
In the Amazon Basin, home to at least 2,700 species of freshwater fish, more than anywhere else in the world, research has identified 20 species of migratory fish that meet CMS protection criteria.
Despite the “alarming” decline, Hogan sees “325 opportunities for collaboration” in the report’s species list, and the Amazon catfish action plan is yet another reason to be cautiously hopeful that change is on the horizon.
“This is a model that didn’t exist 10 years ago for freshwater fish. We now have a model that other countries can follow,” he added.
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