A new report has found that global populations of migratory freshwater fish have declined by an average of 76 percent, across regions, in the last 50 years — warning that such “catastrophic” declines could impact ecosystems, as well as livelihoods, around the world.
Titled Living Planet Index for Migratory Freshwater Fish by the IUCN, the WWF, the World Fish Migration Foundation, and the Zoological Society of London, the report claims to be the first comprehensive global report on the status of migratory fish. The study analyzed 1,406 populations of 247 species of fish from across the globe, and found that their populations had declined on an average of three percent year between 1970 and 2016. The researchers found that the decline has been more pronounced in Europe at 93 percent, and Latin America and the Caribbean at 84 percent — but, the decline stood at a mere 28 percent for North America and 59 percent for Asia-Oceania. However, the researchers also noted that the data available from Asia, Oceania, Africa, and South America was “highly deficient.”
“Freshwaters are disproportionately at risk to human pressures, since they are affected by everything happening in the surrounding catchment. If these fish populations continue to decline, there will be far-reaching consequences for many species which rely on them,” Dr. Michelle Jackson from the Department of Zoology at Oxford University, who was not involved in the study, told The Guardian. Migratory fish are integral to food chains because they provide food for several land animals and birds of prey, besides transporting nutrients by swimming upstream. In addition, species like salmon, trout, and giant catfish are also critical for food security and livelihoods of millions of people around the world.
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Researchers believe that the decline can be attributed to thousands of dams around the world, over-fishing, water pollution, and now, climate change as well. For instance, reportedly the recent Australian wildfires killed large numbers of fish due to ash washing into the rivers. However, dams remain one of the biggest threats. “For migratory fish, there’s nothing worse than a dam. Almost without exception, where dams have been removed, you see populations bounce back, often much more quickly than anyone anticipated,” Zeb Hogan, a biologist from the University of Nevada, and one of the authors of the study, noted.
But, the positive takeaway is that it’s not too late. The report says that interventions like reducing pollution, imposing restrictions on fishing, and allowing rivers to flow more freely and naturally by removing dams, especially those that are “environmentally [more] damaging than others because [of] how they are place[ed], design[ed], and operate[d],” could still significantly alter the course of the decline. In fact, when the migratory fish don’t face threats, their populations often increase, according to the researchers.
“Saving migratory fish does not necessarily require big financial investments, but a change in current practices. What we are hoping is that this report will provide a wake-up call to governments and decision-makers to take action before it’s too late,” Lee Baumgartner, a freshwater fish ecologist at Charles Sturt University in Australia, who contributed to the report, told National Geographic.
