The world’s migratory freshwater fish are in crisis, with their numbers plummeting by an estimated 81% over the last half century, according to a new report led by the United Nations. The report highlights the alarming decline of species like the golden mahseer and goonch catfish, which are now being prioritized for global conservation efforts. Scientists assessed over 15. 000 species of freshwater migratory fish, finding that these creatures are vital to the livelihoods of hundreds of millions of people around the world.

Threats to Migratory Fish Populations

The report reveals that overfishing, pollution, and habitat destruction are the primary causes of the sharp decline; Dams and other physical barriers have fragmented river systems, making it difficult for fish to reach their spawning grounds. According to Dr. Zeb Hogan, co-author of the report and professor of biology at the University of Nevada, Reno, these fish are not only important for food but also for cultural and spiritual practices in many communities.

“Freshwater fish support hundreds of millions of people around the world, so for humans, they’re very important,” Hogan said. “You have fish that can get over 650 lb (295kg) that can migrate over 7,000 miles. 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.”

The report also highlights the cultural significance of some of the species. The golden mahseer, for instance, is known as the “tiger of the river” in the Himalayas and holds deep spiritual value for local communities. Michele Thieme, deputy lead for freshwater at World Wildlife Fund US, explained that these fish are facing both overfishing and habitat loss, which are compounding the decline.

Barriers to Fish Migration

Dr. Janina Gray, head of science at the environment charity WildFish, emphasized that even small barriers like culverts or weirs can disrupt fish migration. “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.”

In Europe, fish encounter an average of one barrier every kilometer on their migration routes. These barriers are often outdated and could be removed to restore natural water flow. “The cumulative effect on migrating fish is enormous,” Gray said. “We need to think about the whole river system, not just individual barriers.”

Thieme added that habitat loss includes things like dams that fragment river systems and change the natural flow regime, which results in fish not being able to connect to their spawning habitats. “The golden mahseer is an iconic fish of the Himalayas. It’s 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.

Global Conservation Efforts

The report calls for the inclusion of 30 priority fish species in the Convention on the Conservation of Migratory Species (CMS), a global UN treaty signed in 1979. The treaty requires countries to work together to protect migrating species of all kinds. The UN is now proposing that these 30 fish species be added to the treaty at its annual meeting in three years’ time.

Professor Hogan said that many of these species will cross country borders on their migrations, requiring coordinated efforts between governments to tackle these threats and ensure the recovery of national stocks. “Most species will cross country borders on their mammoth migrations. This requires coordinated efforts between governments to tackle these threats and ensure the recovery of national stocks,” Hogan said.

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 the focus has been on more well-known, visible species like big cats, antelope, whales, and dolphins. “It’s 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.”

With the decline in migratory fish populations, the report is a wake-up call for governments, conservationists, and communities around the world. The urgency of the situation is clear, and the need for action is now more pressing than ever.