Migrating Freshwater Fish Populations Have Declined 81% Since 1970, Report Finds

Ahead of World Fish Migration Day on May 25, a new Living Planet Index report has revealed major declines in migratory freshwater fish since 1970. According to the findings, migrating freshwater fish populations have declined 81% from 1970 to 2020.

The Living Planet Index Migratory Freshwater Fishes report focused on data for migrating freshwater fish, or fish that move from one habitat to another for breeding and non-breeding in a seasonal or cyclical pattern. The report was a collaboration among the World Fish Migration Foundation, Zoological Society of London (ZSL), International Union for Conservation of Nature (IUCN), The Nature Conservancy (TNC), Wetlands International and World Wildlife Fund (WWF).

On average, the index of 1,864 monitored populations of 284 migratory freshwater fish species from around the world revealed an 81% decline since 1970, leading to an average 3.3% decline per year. In Latin America and the Caribbean, the report noted an average decline of 91%, and Europe’s migratory freshwater fish have declined by about 75%.

“The catastrophic decline in migratory fish populations is a deafening wake-up call for the world. We must act now to save these keystone species and their rivers,” Herman Wanningen, founder of the World Fish Migration Foundation, said in a press release. “Migratory fish are central to the cultures of many Indigenous Peoples, nourish millions of people across the globe, and sustain a vast web of species and ecosystems. We cannot continue to let them slip silently away.”

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Although the report found smaller declines in North America, about 35%, and Asia-Oceania, about 28%, the authors explained they had deficient data for these areas, and they did not have enough data to produce an average for migratory freshwater fish in Africa.

Many factors have contributed to the declining populations. According to the report, habitat degradation, loss and alterations, such as building dams in rivers or clearing wetlands for agriculture, made up about half of threats to the fish. Overexploitation made up nearly one-third of the threats.

But in the past 30 years, other threats are becoming more prominent, such as the warming waters and other effects of climate change and increasing pollution in freshwater areas.

Aside from being important parts of their ecosystems, freshwater fish are also an important food source globally, particularly for areas that may face food scarcity.

“In the face of declining migratory freshwater fish populations, urgent collective action is imperative,” Michele Thieme, deputy director of freshwater at WWF-US, said in a statement. “Prioritizing river protection, restoration, and connectivity is key to safeguarding these species, which provide food and livelihoods for millions of people around the world.”

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Not all species have experienced declines, though, and the report highlighted that managed habitats and fisheries helped minimize declines for some populations. Management activities including fishing restrictions, no-take zones and bycatch reductions helped reduce declining populations of freshwater fish. Some populations also experienced increasing numbers.

In addition to improved management and monitoring, the report authors suggested removing of barriers such as dams, preserving and restoring rivers, promoting public and political engagement on freshwater fish conservation and increasing international collaboration efforts to save migratory freshwater fish.

^{Migrating Clanwilliam sandfish in South Africa. Jeremy Shelton / World Wildlife Fund}