Salmon, eels and sturgeon heading towards extinction as migratory fish populations collapse

Hundreds of fish species have been recommended for urgent conservation as part of a landmark new report.

The Global Assessment of Migratory Freshwater Fishes examines the health of almost 15,000 species, ranging from catfish and sturgeon to eels and trout. It reveals a crisis beneath the surface of rivers and lakes. The populations of these animals are in freefall, with numbers of the largest species having dropped by a shocking 94% since 1970.

These declines are being driven by a multitude of factors, including dams that cut off fishes from vital habitats and overharvesting that leaves their populations too small to recover. This is then compounded by a lack of consistent regulation – fishes migrating along a river might be protected in some countries but aren’t in others.

To combat this, the report recommends that 325 species should be considered for global conservation efforts under the Convention on the Conservation of Migratory Species of Wild Animals (CMS). The lead author, Dr Zeb Hogan, says that international cooperation is crucial to ensure the survival of these species.

“Many of the world’s great wildlife migrations take place underwater,” Zeb says. “This assessment shows that migratory freshwater fish are in serious trouble, and that protecting them will require countries to work together to keep rivers connected, productive, and full of life.”

Amy Fraenkel, the CMS Executive Secretary, adds that the health of migratory freshwater fish populations has previously been overlooked and needs to change.

“This new assessment highlights a major priority for the conservation of migratory species and their habitats, that has not had adequate focus to date,” says Amy. “By aligning science, policy and international cooperation, governments can safeguard the world’s remaining great freshwater fish migrations and the communities and ecosystems that depend on them.”

What threats do migratory fishes face?

Around 19,000 species of freshwater fishes have been named so far. They’re found on every continent except Antarctica, and live in a wide variety of habitats, from brooks and streams to rivers and lakes.

Some areas of the world are particularly diverse, with the lakes of eastern Africa home to more than 1,500 different cichlids – a group of fishes that includes animals such as the tilapia. Many fishes also live in large rivers, with the Amazon, Congo and Mekong supporting thousands of species between them.

While some fish spend their lives in one part of a body of water, around 1,200 species migrate at some point in their lives. The dorado catfish has one of the longest migrations, covering 11,000 kilometres during its lifetime as it journeys from the Andes to the mouth of the Amazon and back.

Unfortunately, freshwater habitats are among the most threatened on Earth, as habitat destruction, pollution and invasive species take their toll. As a result, a quarter of all freshwater species are thought to be at risk of extinction.

Migratory species face additional pressures that make it even harder for them to survive. The construction of dams can stop species, such as the Mekong River catfish, from reaching their spawning or feeding grounds. Meanwhile water abstraction can cause lakes to dry up and rivers to be cut off from the sea.

However, despite the threats facing freshwater fishes, only 24 species of these animals are currently listed under the CMS. Many of these are sturgeons, which are highly endangered because of overharvesting for caviar, but species such as the European eel and a variety of catfish are also included.

While listing on the CMS can help to boost protections and habitat restoration for these animals, it’s not a silver bullet. The Chinese paddlefish, for example, was declared extinct in 2022 after attempts to save the species were unable to turn its fortunes around.

By listing the recommended species sooner rather than later, it’s hoped they’ll be able to avoid the same fate.

Priorities for conservation

Of the 325 species that are being considered for the list, the report recommends a core group of 30 that should be added as a priority.

These include the European river and brook lampreys, jawless fishes that were once widespread but have suffered from the impacts of blocked rivers and pollution. As a result, they’re currently considered Near Threatened. The report recommends that changes are made to weirs and other small barriers to allow these animals through so that their status doesn’t worsen.

Meanwhile, the recently rediscovered leopard barbel is Critically Endangered due to the construction of dams and water abstraction in Turkey, Syria and nearby nations. To keep this species from disappearing for good, the report urges these countries to make new agreements on the flow of water and wildlife between them.

Even well-known species, such as the Atlantic salmon, are also recommended for priority listing. Wild populations are estimated to have declined by around a quarter since 2006 as a result of factors such as pollution, disease and river barriers.

Reversing the fall in migratory fish numbers will take time and won’t always be straightforward. But it’ll be worth it. Restoring habitats that migratory fish rely on, such as mangrove forests, will benefit many other plants and animals as well.

More sustainable fish populations will also help communities that rely on these fishes for food and a source of income. Implementing new rules around where and when fish can be caught will help to ensure both people and the planet can thrive.

To focus conservation efforts, the report recommends prioritising certain rivers, such as the Amazon, the Danube and the Mekong. In these areas, habitat restoration and other changes would help the widest number of migratory fishes.

What happens next is in the hands of the CMS member states currently meeting in Brazil. Their decisions will have a lasting impact on not just migratory fish, but all of the birds, mammals, reptiles and insects that make epic journeys across the planet.