Populations of migratory river fish around the world have plunged by a “catastrophic” 76% since 1970, an analysis has found.
The decline in migratory fish populations is higher than that for land and ocean animals, whose populations have fallen by an average of 60% in the last 50 years. “Freshwaters are disproportionately at risk to human pressures, since they are affected by everything happening in the surrounding catchment,” said Michelle Jackson, at the University of Oxford.
The fall was even greater in Europe at 93%, and for some groups of fish, with sturgeon and eel populations both down by more than 90%. Populations of sturgeon in the Great Lakes of North America, for example, have dropped by 95% from historic levels.
The average fall in populations was 84% in Latin America, while there has been a 59% decrease in Asia-Oceania, although there is limited data there and not enough from Africa to determine any reliable trend. In North America, the fall was less dramatic, at 28%. This is probably because large declines occurred before 1970, but also as a result of a growing number of dams being removed. “For migratory fish, there’s nothing worse than a dam,” said Zeb Hogan, at the University of Nevada and an author of the new report. Studies have shown only a third of world’s great rivers remain free-flowing, while in Britain, for example, 97% of the river network has been interrupted by human-built structures.
“Catastrophic losses in migratory fish populations show we cannot continue destroying our rivers,” said Arjan Berkhuysen, at the World Fish Migration Foundation. “This has immense consequences for people and nature across the globe. We can and need to act now before these keystone species are lost for good.”