Inland fish feed billions of people across the globe. Yet these fish, which spend all or part of their lives in freshwater, are among the most imperiled organisms in the world – a status which could be exacerbated by climate change.

The effects of climate change on freshwater habitats include warmer water temperatures, decreased dissolved oxygen, changes in streamflow and water availability, and eutrophication. Inland fish are particularly vulnerable to these effects because their habitats are already highly fragmented and isolated due to natural and man-made barriers.

Although scientists know that climate change is an important factor affecting inland fish globally, no comprehensive review of the documented and projected impacts existed – until now. A team led by the USGS National Climate Change and Wildlife Science Center (NCCWSC) completed a systematic review of the literature on this topic, reviewing over 600 papers. The synthesis aims to reveal generalizable patterns of climate change effects on inland fish at a global scale, highlight major research gaps, and identify commonly cited management recommendations for addressing these impacts.

Overall, the team found that there has been a greater focus on projecting the effects of climate change on inland fish (65% of studies) than on documenting observed impacts (35%). However, studies focused on documenting the effects of climate change are increasing in number. The authors also found that published studies are not evenly distributed geographically, with most studies focusing on the U.S. and Europe and very few on South America, Africa, and Asia.

Of the different thermal guilds, a majority of the literature focuses on coldwater and coolwater fish species. For example, salmonids (such as salmon and trout) were disproportionately studied compared to other families. In terms of the projected and documented effects, the majority of studies identified contractions in fish distribution, and many identified a decrease in abundance– an unsurprising result, as most studies focused on coldwater species. However, several studies did identify that the distributions of certain warmwater species have already and could continue to increase as temperatures warm, demonstrating that climate change could benefit some species but not others.

Researchers and managers are currently working to identify strategies that can effectively address the impacts of climate change on inland fish. The most commonly cited management strategies are those focused on maintaining phenological diversity within and among species and in age structure. Maintaining diversity is a major strategy for encouraging evolutionary processes that could improve fish resiliency to changing conditions, and can be assisted by actions such as increasing stream connectivity and suppressing invasive species and hybrids.