- A new global study reveals an average 81% decline in migratory freshwater fish populations between 1970 and 2020.
- Habitat loss, degradation and overfishing are the main threats to migratory fish, which are crucial for food security, livelihoods and ecosystems worldwide.
- While 65% of species have declined, 31% have shown increases, suggesting that conservation efforts and management strategies can have positive impacts.
- The report calls for stronger monitoring efforts, protection of free-flowing rivers, and meeting global biodiversity goals to address this crisis.
A new global report reveals a stark reality: populations of migratory freshwater fish species, including salmon, trout, eel and sturgeon, are declining dramatically. The 2024 update on the Living Planet Index for Migratory Freshwater Fishes shows an average 81% decrease in these fish populations between 1970 and 2020.
“The catastrophic decline in migratory fish populations is a deafening wake-up call for the world,” said Herman Wanningen, founder of the World Fish Migration Foundation and one of the authors of the report. “We must act now to save these keystone species and their rivers.”
The report analyzed data from 1,864 populations of 284 migratory freshwater fish species across the globe. Contributing to the report were researchers from the World Fish Migration Foundation, the Zoological Society of London (ZSL), the International Union for Conservation of Nature (IUCN), The Nature Conservancy (TNC), Wetlands International and WWF.
The researchers found that fish populations had declined significantly more in some regions than in others. For example, Latin America and the Caribbean experienced the most severe decrease at 91%, while Europe saw a 75% decline. North America showed a 35% decrease, and Asia-Oceania reported a 28% decline. Data for Africa were limited, making it difficult to determine conclusive trends for that continent.
Migratory freshwater fish are species that move between different habitats to complete their life cycles, and can include fish that migrate within freshwater systems, such as rivers and lakes, as well as those that move between freshwater and marine environments.
These far-ranging fish play a crucial role in food security and nutrition for millions of people, particularly in vulnerable communities across Asia, Africa and Latin America. They also support the livelihoods of tens of millions, from local fisheries to the global trade in migratory fish and fish byproducts and the multibillion-dollar recreational fishing industry.
According to the report, habitat loss and degradation, including fragmentation of rivers by dams and other barriers and conversion of wetlands for agriculture, account for half of the threats to migratory fish. Overexploitation (overfishing) is the second most significant factor. The report also notes that increasing pollution and the worsening impacts of climate change contribute to the fall in freshwater migratory fish populations.
“Generally, threats are manyfold and depend on the location and species, but the main ones are overexploitation, and habitat loss and degradation, which also includes the disruption of migration routes through dams and other river barriers,” Stefanie Deinet of ZSL’s Institute of Zoology and a co-author of the report, told Mongabay.
Casey Pennock, an assistant professor at Ohio State University, who was not involved in the report, told Mongabay that the study’s findings might even be conservative. “While the trends [in the report] are alarming, they are likely conservative estimates, even for places with relatively well-studied fish populations such as North America.”
Pennock highlighted data gaps in the study, noting, “There is geographical and taxonomic bias in the data used in this report with data gaps from large portions of North America including the Great Plains, Intermountain West, and American Southwest and Mexico. Many of these regions are home to migratory fish species that have suffered range-wide declines in occurrence and abundance before and since the 1970s.”
“It is quite possible that the situation is actually worse than captured in the report,” Deinet agreed. “Only 30% of migratory freshwater species known to occur in the region are represented in our data set … The expectation is that the decline will continue and even worsen with additional dam construction, for example in the Amazon.”
Despite the grim overall picture, the report does offer some hope. While the majority (65%) of species have declined, nearly one-third (31%) of monitored species have shown increases in population, suggesting that conservation efforts and improved management can have positive impacts.
Fish populations under some form of management fared better than those without, showing less severe declines. The report notes that fisheries management was the most common type of intervention, accounting for 42% of management activities. These efforts included imposing fishing limits, restocking fish populations, reducing bycatch, providing additional food sources, and establishing protected areas where fishing is prohibited. These management practices were most frequently reported in North America and Europe.
The report cautions, however, that fisheries management may not address all threats facing migratory fish populations, particularly those related to habitat loss and degradation. It highlights several strategies to address declines, such as habitat restoration, dam removals, the creation of conservation sanctuaries, and legal protection.
There’s currently increasing momentum for dam removal in Europe and the United States. In 2023, Europe removed 487 river barriers, a 50% increase over the previous year’s record, according to the latest annual report by Dam Removal Europe.
Meanwhile, the largest dam removals in U.S. history are underway along the Klamath River in California and Oregon.
“Prioritizing river protection, restoration, and connectivity is key to safeguarding these species, which provide food and livelihoods for millions of people around the world,” Michele Thieme, deputy director of freshwater at WWF-US, said in a statement.
Nearly 25% of all freshwater fish species are at risk of extinction, according to the IUCN.
“The threats causing declines in migratory fishes are the same for all freshwater fishes. To conserve freshwater fishes, we need to improve connectivity, which is being accomplished in parts of the USA by removing dams or building fish passages,” Pennock said. “Equally, if not more, important, we need to keep water in rivers, which can be challenging for society because humans directly compete with freshwater fishes for water.”
The report concludes with a call for stronger monitoring efforts, especially in underrepresented regions like Asia, Africa and South America. The study also emphasizes the need to meet the goals set in the Kunming-Montreal Global Biodiversity Framework, which aims to protect 30% of inland waters and restore 30% of degraded inland waters, as well as to protect and restore free-flowing rivers through basin-wide planning.
Other recommendations include supporting the Global Swimways initiative, which identifies and prioritizes key river migration routes; listing more freshwater migratory fish species on the Convention on Migratory Species; and meeting the Freshwater Challenge’s goal of restoring 300,000 kilometers (186,000 miles) of degraded rivers globally.
“Migratory fish are central to the cultures of many Indigenous peoples, nourish millions of people across the globe, and sustain a vast web of species and ecosystems,” Wanningen said. “We cannot continue to let them slip silently away.”
Banner image of fishers catching a white sturgeon on the Fraser River in the Northwestern US, courtesy of Zeb Hogan.
Liz Kimbrough is a staff writer for Mongabay and holds a Ph.D. in ecology and evolutionary biology from Tulane University, where she studied the microbiomes of trees. View more of her reporting here.
‘Chasing giants’: Q&A with megafish biologist and author Zeb Hogan
Citations:
Deinet, S., Flint, R., Puleston, H., Baratech, A., Royte, J., Thieme, M. L., Nagy, S., Hogan, Z. S., Januchowski-Hartley, S. and Wanningen, H. (2024) The Living Planet Index (LPI) for migratory freshwater fish 2024 update – Technical Report. World Fish Migration Foundation, The Netherlands.
Mouchlianitis F.A. (2024). Dam Removal Progress 2023. World Fish Migration Foundation
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