A new UN report has revealed a steep decline in migratory fish populations across the globe, with numbers of these species dropping by an estimated 81% in the last half century. The report, which assessed more than 15,000 species of freshwater migratory fish, highlights the growing threat to these species from dams, pollution, and overfishing. The findings have sparked a global push to protect these fish, which are vital for the livelihoods of hundreds of millions of people.

Global Decline in Freshwater Migratory Fish

The report, published by the UN, states that freshwater migratory fish make up half of all fish species, yet they have long been overlooked in conservation efforts. The study found that over 15,000 species were evaluated, with 325 identified as needing urgent attention. Of these, 30 were prioritized for inclusion in a global agreement to protect migratory species.

Dr. Zeb Hogan, co-author of the report and professor of biology at the University of Nevada, Reno, emphasized the importance of these fish. ‘Freshwater fish support hundreds of millions of people around the world, so for humans, they’re very important,’ he said. ‘They provide enough food for 200 million people globally and have immense diversity that needs protection.’

Hogan described the range of species, from those that can weigh over 295kg and migrate over 7,000 miles to smaller, more delicate species. ‘You have fish that can get over 650 lb (295kg) that can migrate over 7,000 miles,’ he said. ‘Every shape and size of animal you can imagine, these beautiful golden dorado that make long-distance migrations in South America, tropical eels that are moving thousands of miles in Oceania.’

Threats to Migratory Fish Populations

The decline in migratory fish populations is largely attributed to overfishing and habitat loss. Michele Thieme, deputy lead for freshwater at World Wildlife Fund US, explained that the golden mahseer, an iconic fish of the Himalayas, is one of the species facing these threats. ‘The golden mahseer is called the tiger of the river, and many of the people in that region value that fish for cultural and spiritual practices that go far beyond the economic values,’ she said.

Habitat loss includes things like dams that fragment river systems and can change the natural flow regime of a river, which results in fish not being able to connect to their spawning habitats. Thieme said that disruption to migration is an issue that is particularly prevalent in Europe, where fish encounter a barrier to their routes every kilometre (0.6 miles) on average.

Dr. Janina Gray, head of science at environment charity WildFish, said that the cumulative effect on migrating fish is enormous. ‘It can have a massive impact in terms of the energy reserves fish are using to get over the [barriers],’ she said. ‘That makes them more susceptible to disease. They’re more likely to get predated. They will spawn in suboptimal grounds.’

International Cooperation for Fish Conservation

Most species will cross country borders on their mammoth migrations, requiring coordinated efforts between governments to tackle these threats and ensure the recovery of national stocks. Prof Hogan, co-author of the study, said that the Convention on the Conservation of Migratory Species (CMS) is a global UN treaty signed in 1979 that commits countries to work together to protect migrating species of all kinds.

The UN is now proposing that the 30 fish species be added to the treaty at its annual meeting in three years’ time. The Saiga antelope is an example of a species that has benefited from being listed under the convention. In 2015, the antelope suffered a mass die-off and it was feared that the Ice Age survivors would become extinct. But an international anti-poaching team was established and since then population levels have rebounded to more than a million.

Amy Fraenkel, the UN Executive Secretary for the Convention on Migratory Species (CMS), said that the focus has clearly been on some of the more well-known, more visible species, such as the big cats, on antelope, on whales, on dolphins. ‘It was now the turn of migratory freshwater fish to benefit from coordinated action,’ she said. ‘The focus of the convention on mammalian species over others like fish and insects has previously been a criticism of the agreement.’

The report also highlights the need for international cooperation in protecting migratory fish, which often cross national borders. For example, the Allis Shad, River Lamprey, Brook Lamprey, and Atlantic Salmon are some of the fish found in the UK that are now being prioritized for conservation. These species are not only ecologically significant but also have cultural and economic value for local communities.

As the report indicates, the decline in migratory fish populations is a pressing issue that requires immediate action. With over 81% of these species having disappeared in the last 50 years, the need for global cooperation and coordinated efforts is more urgent than ever. The inclusion of these 30 priority fish in the CMS treaty is a critical step towards their recovery and the preservation of their vital role in ecosystems and human livelihoods worldwide.