- A new report finds that migratory freshwater fish species have declined on a global scale by 76% since 1970, with the highest drops experienced in Europe.
- The biggest threat to migratory freshwater fish is habitat degradation or alteration, such as dams, culverts and road crossings, while other threats include habitat loss, overfishing, pollution, and climate change.
- The authors of the report recommend taking actions to help restore migratory freshwater fish populations, including the restoration of free-flowing rivers by removing dams and other obstructions.
Migratory freshwater fish are in big trouble. According to a new report, monitored populations of migratory freshwater fish have dropped on average by 76% since 1970, which is a higher rate of decline than among marine and terrestrial species.
The report, published this week by the World Fish Migration Foundation, is the first global assessment of migratory freshwater fish species. Using information from the Living Planet Index project, run by the Zoological Society of London (ZSL) and WWF, the report draws on data from 1,406 populations of 247 species from regions across the globe. However, it notes there was deficient data for Africa, Asia, Oceania and South America.
“The 76% average decline in migratory freshwater fish is one of the worst we’ve found in our work but we think migratory freshwater fish might be in even greater peril than that,” Stefanie Deinet, lead author of the study, told Mongabay in an email. “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 not upwards.”
A freshwater migratory fish is defined as a fish that travels between critical habitats to spawn or feed, either using freshwater exclusively or partially. This includes catadromous fish, such as European eels (Anguilla anguilla), which migrate downriver to the sea to spawn, and anadromous fish, such as Atlantic sturgeon (Acipenser oxyrinchus), which travel upriver from the sea to spawn. There are also amphidromous fish, like mountain mullets (Agonostomus monticola), that move between saltwater and freshwater, although not for breeding purposes, and potamodromous fish, such as white sturgeon (Acipenser transmontanus), which migrate exclusively within freshwater systems.
On average, the biggest threat to freshwater migratory fish was obstructions to free-flowing rivers, such as dams, culverts and road crossings, which prevent fish from accessing locations required for food or breeding purposes, according to the report. Other threats include habitat loss, overfishing, pollutants, invasive species, disease, and climate change.
The biggest decline in migratory freshwater fish was found in Europe, which has experienced an average 93% decrease, while Latin America and the Caribbean followed closely behind with an 84% drop.
With millions of people depending on migratory fish as a food source, declines could lead to global food security issues, the report suggests. The loss of migratory freshwater fish in aquatic systems could also have dire consequences for the environment.
“Rivers and migrations are the connective tissue of our planet — and migratory fish are bellwethers for not just rivers, but for the countless other systems they connect, from the deep sea to coastal forests. Losing these fish means losing so much more,” Jeffrey Parrish, global managing director for the Protect Oceans, Land and Water program at The Nature Conservancy, said in a statement. “By factoring in these species and systems into sustainable energy and food production, and by investing in their protection and restoration, we can bring them back.”
At the end of the report, the authors make several recommendations to help restore global populations of migratory freshwater fish: allowing rivers to flow naturally; restoring river connectivity through better planning of dams and other structures; curbing overfishing; reducing pollution; controlling invasive species; and protecting the critical habitats that species depend upon.
“To address declines, we need to restore and protect these species and their habitat, and ensure that the barriers to their migration are removed and flow regimes are restored,” Deinet said. “We also need to ensure that we don’t over-consume, reduce our carbon and plastic footprint, and take seriously the need to address climate change. To achieve this, we need to engage with both policy-makers and the public.
“If we do nothing, we run the risk of ever smaller populations of these species, and of eventually losing some of these species too,” she added. “This would not only threaten an important source of food and income for millions of people but also have knock-on effects on the ecosystems on which migratory fish depend.”
Banner image caption: A migratory freshwater fish swimming up river. Image by Petteri Hautamaa / WWF Finland.
Elizabeth Claire Alberts is a staff writer for Mongabay. Follow her on Twitter @ECAlberts.
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