Image description: Salmon jumping upstream. Image by Danny Moore from Pixabay.
Migratory freshwater fish populations vital to river health and sustaining the livelihoods of millions of people are in freefall and risk collapse, a major UN assessment has warned.
Freshwater fish face multiple threats and are “among the most imperiled vertebrates”, according to the most comprehensive assessment to date, published at the opening of the COP15 summit on migratory species in Brazil.
Epic river migrations of fish rapidly collapsing
For centuries fish migrations have been regarded predictable as the seasons. Salmon, sturgeon, giant catfish and many other species moved through rivers in vast numbers, guided by rising water, flood pulses and evolved biological cues.
Reliant on unimpeded passage to move between spawning and feeding grounds, which can span across borders, increasing disruptions to the epic voyages of hundreds of species along the world’s great rivers now threatens their very survival.
These massive migrations, which rival those of the zebra and wildebeest across the Serengeti, are under mounting pressure from habitat destruction, overfishing and water pollution from the Amazon to the Danube.
Migratory freshwater fish are a vital protein source for people and animals around the globe, underpinning some of the world’s largest inland fisheries, but populations worldwide have plunged by about 81% since 1970, according to the analysis by the UN’s convention on the conservation of migratory species (CMS) and led by Dr Zeb Hogan at the University of Nevada in the US.
Populations of Mekong giant catfish, European eel and various sturgeon species are among those that have been decimated in recent decades due to man-made pressures that include the construction of dams and harvest for caviar.
Some have already been declared extinct, such as the Chinese Paddlefish, while others are functionally reliant on captive breeding stock and reintroductions to support wild populations.
International cooperation needed to reverse the declining trend
Half of the Earth’s land surface lies within river basins shared by more than one country, but the report found the collapse of river migrations was a largely overlooked biodiversity crisis. It assessed data on more than 15,000 species of freshwater fish and found 325 that crossed borders and could meet the criteria for being listed for protective action. Only 24 have been listed to date, mostly sturgeon, which have long been targeted for caviar.
Species including salmon, eels, and lampreys are among those to be considered during the March 23-29 meeting in Campo Verde.
Of these, the vast majority are found in Asia, followed by South America and Europe.
The river basins deemed priorities are the Amazon and La Plata-Parana in South America, the Danube in Europe, the Mekong and the Ganges-Brahmaputra in Asia and the Nile in Africa. Brazil and other countries have already proposed a decade-long action plan for migratory catfish, which could be a model for other basins.
“This assessment shows that migratory freshwater fish are in serious trouble, and that protecting them will require countries to work together to keep rivers connected, productive, and full of life,” said Zeb Hogan, the lead author of the assessment, in a statement.