• by Kizito Makoye (rufiji, tanzania)
• Tuesday, March 24, 2026
• Inter Press Service

RUFIJI, Tanzania, March 24 (IPS) - By the time the auction begins at Nangurukuru fish market in Tanzania’s southern Lindi region, the crisis is already visible. Wooden canoes that once returned from the Rufiji River with heavy catches now bring only a fraction of what they used to. Traders scan for the long-whiskered catfish that once defined the market but find none.

“The big Kambale are hard to find these days,” says 68-year-old fisherman Hamisi Juma.

For generations, seasonal floods brought migratory catfish and other freshwater species along the Rufiji River, allowing them to feed, breed, and replenish their numbers. That cycle sustained fish stocks and thousands of livelihoods.

What is happening on the Rufiji reflects a wider collapse in migratory freshwater fish that are vital to food security and incomes across Africa. For river communities in Tanzania, the disappearance of these species is not only an environmental crisis but also an economic and social one.

Migratory freshwater fish, which travel long distances within rivers or between them and the sea to spawn and feed, are rapidly disappearing. Scientists say they are among the world’s most threatened vertebrates, driven into decline by river fragmentation, pollution, overfishing, and climate change. Their survival depends on rivers flowing freely, yet across Africa and elsewhere those rivers are increasingly being dammed, diverted and degraded.

“Fish is our main source of protein,” says Asha Mrope, a trader at Nangurukuru market. “When they disappear, everybody at home is affected.”

Dr Zeb Hogan, lead author of a new global assessment on migratory freshwater fishes, says the decline poses a direct threat to food security.

“Freshwater fisheries provide food and livelihoods for hundreds of millions of people around the world, especially in rural and low-income countries,” he tells Inter Press Service (IPS). “These fisheries are worth billions of dollars and provide the majority of protein to people living along rivers with major fisheries.”

In Tanzania, that dependence is visible from the Rufiji to Lake Victoria.

“Fish from Lake Victoria, which contains for example, stocks of Nile perch and other species that are shared between Tanzania, Uganda and Kenya, are a staple food and provide food for millions of people living in northern Tanzania,” Hogan says.

The report’s warning that migratory freshwater fish are among the most endangered vertebrates is therefore more than a biological alarm. In practical terms, it points to a growing food security threat for communities with few affordable alternatives.

The Shortened Migratory Route

To understand the scale of the problem, it helps to follow the fish themselves.

Many species in the Rufiji depend on seasonal floods to move through rivers, wetlands and floodplains where they feed and reproduce. When that rhythm is broken, the damage spreads quickly through the ecosystem.

“When you block a river, you technically destroy biological signals that fish have followed for thousands of years,” says Hilda Mpangala, a scientist at the University of Dar es Salaam.

Hogan says dams disrupt that cycle in several ways.

“Dams disrupt fish migrations – by blocking upstream spawning migrations, by slowing downstream dispersal of young fish, and by modifying river flows that are needed to trigger migrations or distribute young fish to flood plains,” he says.

When fish cannot reach spawning and nursery grounds, populations fall and catches shrink.

The Julius Nyerere Hydropower Dam, one of Africa’s biggest infrastructure projects, captures the dilemma. For Tanzania, it promises more electricity and economic growth. But it also sits on one of the country’s most ecologically important rivers.

For Hogan, the principle is simple: “Keeping rivers healthy and free-flowing keeps aquatic ecosystems full of fish for the benefit of people and the environment.”

Declining Kambale

Seasoned fishermen along the Rufiji remember a different river.

“We used to catch Kambale weighing 30kg. These days you can hardly get any,” says Juma.

Large freshwater fish, often the most valuable for food and income, are declining rapidly and are especially vulnerable to dams, habitat loss and overfishing.

“Big fish need space and time to multiply,” says Juma.

In many communities, the loss of fish means more than lost income. Fish are tied to memory, ceremony and identity. Their absence is felt not only in household meals but also in the stories people tell about the river and the life it once sustained.

Climate Change a Factor

Climate change is worsening the pressure. Across East Africa, shifting rainfall patterns are altering river flows and weakening the flood cycles many fish depend on to migrate and reproduce. Long droughts lower water levels, while sudden heavy rains can trigger destructive flooding.

At the same time, pollution from farming and industry, habitat degradation and overfishing is placing rivers under even greater strain. With fewer fish available, some fishers turn to smaller-mesh nets or illegal methods that trap juvenile fish before they have a chance to reproduce.

A Regional Problem

Across Africa, major river systems such as the Nile, the Congo and the Niger support millions of people and contain some of the world’s richest freshwater biodiversity. Yet many of these rivers are under growing pressure from dams, pollution, climate shocks and weak management.

A new United Nations-backed Global Assessment of Migratory Freshwater Fishes, released today under the Convention on Migratory Species, estimates that migratory freshwater fish populations have declined by 81 percent since 1970, one of the sharpest falls recorded for any group of vertebrates. The report identifies 325 species in urgent need of international conservation action, including 42 in Africa.

“These are some of the world’s great wildlife migrations,” Hogan says. “But they are happening out of sight – and they are collapsing.”

The challenge is especially acute in Africa, where many rivers and lakes cross national borders. The report identifies the Nile, Congo and Niger-Lake Chad systems among priority basins for cooperation.

“Freshwater fish, while extremely important to people and ecosystems, are often overlooked,” he says. “Their migrations, which in terms of sheer biomass can rival the great migrations of zebras and wildebeests across the Serengeti, happen unseen, underwater, and so it’s hard to appreciate their significance and their scale.”

The political challenge is just as daunting.

“The benefits of healthy stocks of migratory fish are often diffused. Millions of people living in rural areas benefit, and those people may not be the decision-makers when it comes to making policy about river development,” Hogan says. “So there is a disconnect between the importance of migratory fish to people and ecosystems and the value assigned to migratory fish by policymakers and developers.”

That matters deeply in Africa, where rivers and lakes routinely cross national borders.

“This is why it’s so important for countries to work together to improve management and protection of migratory fish and fish stocks that straddle international borders,” Hogan says. “Over 49 percent of the Earth’s surface is covered by transboundary rivers – so this is not a local or national issue; it’s a global issue that requires international cooperation.”

“Fish do not recognise borders,” Mpangala says. “But too often our policies do.”

Food security at risk

For policymakers, the decline of migratory fish exposes a difficult tension between development and ecological survival. Hydropower can help expand electricity access and fuel economic growth. But when river systems are altered without fully accounting for ecological costs, the consequences can be severe, especially for poor communities that depend directly on fisheries.

Hogan frames the balance in pragmatic terms.

“Yes, hydropower is critical for development,” he says, “so the key is to maximise the benefits from hydropower while at the same time minimising environmental costs.”

That, he argues, requires far better choices than are often made.

“This can be done by siting dams in appropriate locations and designing and operating them well. A good dam is one where the economic benefits far outweigh the environmental costs. Unfortunately there are many ‘bad’ dams being built where the economic benefits are far less than the environmental costs.”

He says some old structures should simply go.

“Old and outdated dams that no longer serve a purpose can also be removed, enabling migratory fish to access historic habitats. This approach has been very successful at restoring stocks of migratory fish.”

At the same time, “we can also set aside some rivers, in protected areas for example, as free-flowing rivers.” And as countries pursue energy security, “another solution which is increasingly being considered is other sources of renewable energy, such as solar and wind.”

In Tanzania, where population growth and urbanisation are increasing demand for both food and energy, that balancing act is becoming more urgent.

“If we lose our fisheries, we are also losing our food, jobs and our way of life,” says Mrope.

Searching for solutions

Experts say the decline can still be slowed – and in some cases reversed – if governments act quickly. Among the most urgent steps are protecting migration corridors, restoring environmental flows, improving fish passage around dams, tightening regulation of fishing practices and investing in better research and monitoring. Many migratory species remain poorly studied, especially in Africa, making effective policy harder.

For Hogan, the most realistic solutions start with the people who know the rivers best.

“Work with local communities to empower them to improve management of fisheries, and connect communities with each other and government to work together to improve management,” he says.

He also argues that countries sharing rivers must cooperate more closely, while fishers’ knowledge should be treated as part of the solution, not pushed to the margins.

“Countries need to work together to manage migratory fish: share data, set common guidelines and regulations, and agree to appropriately value migratory fish and fisheries when making development decisions,” Hogan says.

And he insists that local knowledge must move closer to the centre of policymaking.

“Fishers in local communities are among the most knowledgeable people about migratory fish and ways to protect them; local people should be empowered to share their knowledge.”

He adds that “key fish migration corridors and spawning and rearing habitats should be identified and protected.”

Some of that work, he says, has already begun.

“There are global efforts, working with local communities, to collect knowledge about migratory fish, key migration corridors, and critical habitats that need to be protected.”

A Quiet Warning

Back in Nangurukuru, the market begins to thin as the sun rises higher. The little fish that has arrived is quickly sold. Traders gather their baskets. Fishermen sit in the shade mending nets, preparing for another uncertain day on the river.

“The river is still there,” Juma says. “But it is not the same river we knew.”

IPS UN Bureau Report

© Inter Press Service (20260324121010) — All Rights Reserved. Original source: Inter Press Service

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