Migratory fish populations have crashed by more than 80% since 1970, new findings show.
Populations are declining in all regions of the world, but this is happening most rapidly in South America and the Caribbean, where the abundance of these species has fallen by 91% over the past 50 years.
This region has the world’s largest freshwater migrations, but dams, mining and people diverting water are destroying river ecosystems. In Europe, the population of migratory freshwater fish has fallen by 75%, according to the latest update to the Living Planet Index.
Migratory freshwater fish rely partially or exclusively on freshwater systems – some are born at sea and migrate back into freshwater, or vice versa. In some cases they can swim the width of entire continents and then return to the current in which they were born.
They form the basis for the diet and livelihood of millions of people worldwide. However, many rivers no longer flow freely due to the construction of dams and other barriers, which block species’ migrations. There is an estimated 1.2 m barriers across European rivers.
Other causes of decline include pollution from urban and industrial wastewater, and runoff from roads and farms. Climate breakdown is also changing habitats and the availability of fresh water. Unsustainable fishing is another threat.
Herman Wanningen, founder of the World Fish Migration Foundation, one of the organizations involved in the study, said: “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.
“Migratory fish are central to the cultures of many Indigenous peoples, feed millions of people around the world, and sustain a vast web of species and ecosystems. We cannot continue to let them slip away quietly.”
A quarter of freshwater fish species are threatened with extinctionaccording to the International Union for Conservation of Nature (IUCN), with migratory fish disproportionately threatened.
The report looks at population trends of 284 freshwater fish species. Researchers also noted that there could have been significant declines before 1970, but there was no data for this.
There was also insufficient data to calculate population changes in Africa, but researchers wrote that many species in that region experienced multiple stressors.
Previous research found similar “catastrophic” declines. Authors of the latest report call for better long-term monitoring, rivers to be restored and protected, and the removal of barriers to migration.
Researchers want to find renewable energy alternatives to the thousands of new hydropower dams planned around the world. Last year a record 487 barriers was removed in 15 European countries.
Michele Thieme, deputy director of freshwater for WWF-US, said: “We have the tools, ambition and commitment to reverse the collapse of freshwater fish populations… Prioritizing river protection, restoration and connectivity is key to securing these species.”
Dr David Jacoby, a zoology lecturer at Lancaster University, said while the report confirmed widespread concern about freshwater bodies, “the scale of decline, both regionally and globally, is still shocking”.
“The threats posed by barriers to migration, pollution, water abstraction and climate change are becoming cumulative,” he said, adding that the “huge” impact on migratory species and the impact on the fisheries that sustain them required increased monitoring to helping to reconnect freshwater and marine. ecosystems.
Dr Anthony Acou, from the National Research Institute for Agriculture, food and the Environment (INRAE) in France, pointed out that since many species that migrate between salt and fresh water spent most of their lives in the sea, it was also important to “pressures such as oceanic current change, decline in productivity , in the sea to take into account wind farms, climate change [and] bycatch”.
“To conserve/conserve the species, it is critical to better understand the impact of the pressure on both marine and freshwater habitats to improve our understanding and target effective management measures,” he said.
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