Many freshwater fish species have declined by 76 percent in less than 50 years

Like many migratory fish, chinook salmon are threatened by overfishing, habitat degradation, and dams that block their migration from the sea to upriver spawning grounds. Photo: Cristina Mittermeier, Nat Geo Image Collection.
  • Stefan Lovgren / National Geographic
  • August 18, 2020 11:52 AM

Around the world, migratory freshwater fish numbers are dropping faster than migratory species both on land and in the ocean, a new study finds.

MIGRATORY FRESHWATER FISH are among the most threatened animals on the planet, a new report by a coalition of environmental organizations shows.

The global assessment, described as the first of its kind, found that populations of migratory freshwater fish have declined by 76 percent between 1970 and 2016—a higher rate of decline than both marine and terrestrial migratory species.

“We think migratory freshwater fish might be in even greater peril” than the dramatic drop the report indicates, says the report’s lead author, Stefanie Deinet of the Zoological Society of London (ZSL). “Adding currently missing information from tropical regions where threats of habitat loss and degradation, overexploitation, and climate change have been increasing, will surely bend the curve of loss downwards.”

Published Tuesday on the website of the World Fish Migration Foundation, a nonprofit conservation organization, the study draws upon The Living Planet Index, a database of global biodiversity managed by the ZSL and the World Wildlife Fund for Nature. It finds that Europe has seen the greatest decline in migratory freshwater fish—with populations there plummeting a staggering 93 percent in the past five decades—followed by Latin America and the Caribbean with an 84 percent decline. (It’s not just fish—read about how all freshwater animals face steep declines.)

Epic journeys

Nearly half of the world’s more than 30,000 fish species live in fresh water, and many of them—perhaps most—migrate between habitats for breeding and feeding. Some, such as salmon, move from the sea into rivers to spawn; others, such as the European eel, mature in freshwater but spawn in the ocean. There are also many species of so-called potamodromous fish that migrate strictly within freshwater habitats. They include the Dorado catfish which makes an epic journey from the Andes to the mouth of the Amazon and back, a distance of 7,200 miles.​

Fish migrations serve a wide range of functions within the ecosystem, including the transportation of essential nutrients and larvae from one place to another. Many human populations depend on predictable migrations of fish for their subsistence and livelihoods. (To be continued).

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