How Healthy Rivers Help Save Freshwater Fish From Extinction

Freshwater environments occupy under one per cent of the Earth’s surface, but they sustain a remarkable proportion of the world’s biodiversity. Millions of people also rely on them for food, livelihoods and cultural practices.

Yet fish are vanishing from rivers and lakes worldwide at a worrying pace. Researchers estimate that almost one in three freshwater fish species is now threatened with extinction.

The evidence can be seen on every continent, from redfin pickerel in Maine’s Kennebec River to sturgeon in the Great Lakes.

The loss of fish is about far more than wildlife. It reduces food availability, puts pressure on local economies and disrupts the balance of entire ecosystems.

Global research into freshwater fish

A major worldwide study examined 10,631 freshwater fish species, rather than looking solely at those already known to be in difficulty. Led by researchers at the University of Maine, the work assessed species found in rivers and lakes across the globe.

The researchers used the International Union for Conservation of Nature (IUCN) Red List, the worldwide benchmark for assessing extinction risk, to establish which fish were at risk.

Species classified as Vulnerable, Endangered or Critically Endangered were placed in the imperiled group.

Those assessed as Near Threatened or Least Concern were categorised as non-imperiled. However, this is where the research took a different approach.

Rather than concentrating exclusively on species already moving towards extinction, the team explored a fresh question: what allows certain species to remain safe in the first place?

By prioritising resilience as well as risk, the results may give conservation managers an earlier opportunity to act, protecting species before they enter the danger zone.

AI identifies freshwater fish survival patterns

To investigate patterns across thousands of species, the team used machine learning.

They developed a model capable of finding relationships that people might overlook, drawing on 52 variables from 12 global data sources. These included species characteristics, environmental conditions and economic pressures.

Environmental measures covered climate, water availability, river flow and land cover. The model also incorporated socioeconomic factors, including human population density, gross domestic product, dams, wastewater treatment plants and protected areas.

Taxonomy, which groups species according to shared characteristics, was used to account for wider biological similarities.

In testing, the system performed strongly, accurately predicting whether a species was imperiled 88 percent of the time.

It was particularly effective at recognising species that are presently safe, achieving around 90 percent accuracy, against approximately 81 percent for imperiled species.

This gap points to an important finding. Consistent, healthy conditions tend to produce more recognisable patterns, whereas extinction risk can arise from innumerable combinations of pressures, making it more difficult to address once it has started.

River health shapes fish survival

One of the most direct conclusions of the study is that a fish’s location can matter more than its identity. Environmental and socioeconomic circumstances had a greater influence on conservation status than species traits by themselves.

Water availability, stream power and habitat stability were particularly significant. Fish in areas with dependable water supplies and less severe human disturbance were much more likely to stay non-imperiled.

However, risks increase rapidly when rivers are changed. Hydrogeomorphic diversity, meaning the range of habitat types across a species’ distribution, was a strong predictor of extinction risk.

Broken-up, unconnected river systems restrict access to breeding grounds and seasonal habitats. Dams and other obstructions can prevent migration and isolate populations, making it more difficult for them to persist.

Evolutionary links mattered too. Species that are closely related frequently react in similar ways to environmental pressure, which can help researchers pinpoint vulnerable groups.

Human activity affected results throughout the analysis. Notably, species with either very limited scientific information or substantial research attention were more likely to be classed as imperiled, a trend that could indicate caution in conservation assessments.

Taken together, the findings indicate that connected, healthy rivers with dependable water and moderate human pressure offer freshwater fish their strongest prospects of survival.

What healthy rivers can teach us

“This uses new metrics to identify what is working to keep species from being listed,” said study co-author Dr. Christina Murphy from the University of Maine’s Cooperative Fish and Wildlife Research Unit. “Managers may be able to protect a lot of fish.”

The model draws attention to beneficial conditions, including intact habitats, reliable water systems and moderate human influence. Improving these factors could enable managers to support numerous species at the same time.

“The big takeaways are the socioeconomic impact on conservation potential, and that we are better at identifying what works for species than what doesn’t,” Dr. Murphy said.

“Managers can set up new conservation programs based on what has worked in the past because a lot of species share what works.”

Prevention is better than recovery

“Our results suggest conservation works like human health: the signals of ‘well-being’ are often more consistent than the many pathways to illness,” said study co-author J. Andres Olivos, a postdoctoral researcher at Oregon State University.

“For freshwater fishes, safe conditions tend to be predictable, while extinction risk can come from countless combinations of threats.”

The idea reinforces the case for preventative conservation. Rather than waiting for fish populations to crash, decision-makers can preserve healthy habitats and reduce damaging pressures sooner.

“People sometimes go in to protect species when it’s already too late. With our model, decision makers can deploy resources in advance before a species becomes imperiled,” added Ivan Arsmendi, an associate professor in Oregon State University’s College of Agricultural Sciences.

Saving freshwater fish begins upstream

Freshwater fish are confronted by climate change, dams, pollution, invasive species and habitat loss. Even so, the research provides grounds for hope.

Through effective data, international collaboration and early intervention, rivers and lakes can continue to support abundant life for generations to come.

The study drew on data from Global Dam Watch, HydroWASTE and the World Database on Protected Areas.

The research was published in the journal Nature Communications.