Climate change is pushing freshwater fish toward the poles

Freshwater fish populations near the poles are outperforming their equatorial counterparts due to climate change.

Warming temperatures are creating new habitats at the poleward edges of their ranges, enabling large-bodied migratory species such as Atlantic salmon to thrive.

In a recent study, researchers from the University of Bristol analyzed a dataset that included over 10,000 time series and more than 600 freshwater fish species.

How are fish responding to climate change?

The research highlights a crucial aspect of how animals are responding to climate change, which has driven broad-scale distribution shifts in marine and terrestrial species.

However, the responses of freshwater species have remained less explored.

“Understanding how the population abundance of freshwater species has responded climatic warming over recent decades is important for predicting how they are likely to be impacted by future conditions,” wrote the study authors.

Climate-driven shift in fish habitats

“A common biological response to climatic warming in marine and terrestrial habitats is that populations are increasing at the poleward side of species ranges, as new environments are generated, and populations are declining at the equatorward side of species ranges, as conditions become too warm,” explained study co-author Professor Martin Genner.

Using a multicontinental database, the researchers linked riverine fish population abundance data from 1958 to 2019 with temperature records.

The results showed that across sampled locations, water temperatures increased by an average of 0.21 °C (0.38 °F) per decade. This warming aligns with population trends predicted by climate models, particularly in longer time series spanning over 30 years.

Species benefiting from warming waters

The study found that fish species with specific traits – larger body sizes, higher trophic levels, river-to-sea migratory behaviors, and widespread distributions – exhibited population growth in response to a warming climate.

Examples include brown trout, European perch, and northern pike. These positive trends were more pronounced in cooler, higher-altitude environments, where warming temperatures create favorable conditions.

“These findings indicate that projected future warming will likely lead to widespread shifts in riverine community structure, including abundance declines at the trailing edge of species distributions,” noted Professor Genner.

Looking beyond climate change

While climate change is a significant factor, the researchers aim to assess its relative importance compared to other stressors, such as pollution, habitat modification, and fisheries. Understanding these interactions could be key to developing effective conservation strategies.

“Our study has shown how warming waters are impacting freshwater river fishes, that are both rich in biodiversity and are traditionally important to cultures across the world,” said Professor Genner.

“We hope that shining a light on how climate change can affect freshwater fishes will lead to positive actions to enable their conservation and sustainable use.”

Professor Genner added that we need to learn more about how the impacts of climate change can be lessened through conservation strategies, such as habitat restoration.

Protecting ecosystems from climate change

This research highlights the urgency of addressing climate change’s effects on freshwater fish and marine ecosystems.

By identifying species and regions most vulnerable to warming, policymakers and conservationists can prioritize actions to preserve biodiversity and maintain the cultural and ecological roles of freshwater fish.

Habitat restoration and sustainable management practices may play a critical role in mitigating the impacts of a warming world on these vital ecosystems.

Polar freshwater fish

Polar freshwater fish are uniquely adapted to survive in some of the harshest aquatic environments on Earth.

Species like Arctic char, whitefish, and grayling thrive in cold waters, often below 4°C, where oxygen levels remain high and competition is relatively low compared to temperate zones. These fish exhibit specialized physiological traits, such as antifreeze proteins in their blood, which prevent ice crystals from forming and damaging their tissues.

In addition to their physiological adaptations, many polar freshwater fish display behavioral traits that enhance survival.

For instance, Arctic char can switch between freshwater and saltwater habitats seasonally, optimizing food availability and breeding success. These migratory behaviors also make them key indicators of ecosystem health, as their movements are closely tied to water temperature and ice cover.

Moreover, polar regions often host fewer species compared to more temperate zones, but these ecosystems are vital for global biodiversity.

The limited number of species creates a fragile food web, where climate-driven changes in fish populations can have cascading effects on predators like birds and mammals, as well as on human communities that rely on these fish for sustenance and cultural practices.

The study is published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–