Migratory fish populations have plummeted by over 80% since 1970, according to new research.

This decline is occurring worldwide, with the fastest rates seen in South America and the Caribbean, where populations have dropped by 91% in the last 50 years. This region hosts the world’s largest freshwater migrations, but activities such as dam construction, mining, and water diversion are devastating river ecosystems.

In Europe, migratory freshwater fish populations have decreased by 75%, as reported by the latest Living Planet Index update.

Migratory freshwater fish depend on freshwater systems for part or all of their life cycles. Some species are born at sea and migrate to freshwater to spawn, while others do the reverse. These fish can travel across entire continents to return to their birthplace.

They are crucial for the diets and livelihoods of millions globally. However, many rivers are now impeded by dams and other barriers, hindering these migrations. Europe alone has about 1.2 million barriers across its rivers.

Pollution from urban and industrial wastewater, road and agricultural runoff, and climate change are also contributing to habitat degradation and reduced freshwater availability. Unsustainable fishing practices further threaten these species.

The International Union for Conservation of Nature (IUCN) indicates that a quarter of freshwater fish species face extinction, with migratory fish being particularly vulnerable.

The report examined population trends of 284 freshwater fish species, noting potential significant declines before 1970 for which data is unavailable. Insufficient data also prevented population change calculations in Africa, although many species there face multiple stressors.

Previous research has similarly documented these drastic declines. The latest report emphasises the need for improved long-term monitoring, river restoration and protection, and the removal of migration barriers.

Researchers advocate for renewable energy alternatives to the numerous new hydropower dams planned globally. Notably, last year saw a record 487 barriers removed in 15 European countries.

 

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