‘A canary in the coal mine’: Even fish adapted to dry climates are struggling amid rising temps, droughts
Study finds fish diversity in arid regions of U.S. and Australia dropped amid reduced water availability
University at Buffalo
image:
A desert fish sampled from the Gila River, New Mexico, in 2011.
view moreCredit: Corey Krabbenhoft/University at Buffalo
BUFFALO, N.Y. — Fish living in warm and arid climates are used to adversity. High temperatures and droughts can routinely cause the streams they call home to stop flowing or dry out altogether.
Yet even fish adapted to these harsh conditions may be buckling under the stress of a changing climate.
A research team co-led by the University at Buffalo has analyzed four decades of data from nearly 1,500 streams across dry regions of the United States and Australia, and found that the number of fish species there has declined amid rising temperatures and reduced precipitation and streamflow.
While their statistical analysis, published Sept. 1 in Ecology and Evolution, could not directly link the species decline with the water availability decline, the researchers warn it could nevertheless be a warning sign given that the number of water-limited ecosystems is expected to expand globally.
“If highly adapted fish can't hack it in warm and dry climates, it doesn’t bode well for fish that are used to much milder climates,” says the study’s first and corresponding author, Corey Krabbenhoft, PhD, assistant professor in the UB Department of Biological Sciences, within the College of Arts and Sciences. “Fish living in dry climates are a canary in the coal mine when it comes to climate change, so it’s crucial we have a full understanding of what is causing this drop in their species diversity.”
No flow can hurt fish
Streamflow is crucial to fish health. Connecting different bodies of water, it allows fish to find food, reproduce and carry out their other life functions. It also helps provide oxygen and reduces the impact of sediments and contaminants.
Yet certain species of freshwater fish find a way to survive in intermittent streams — streams that only flow during certain parts of the year. Over half of streams and rivers in the U.S. are intermittent, and that figure jumps to 80% in the southwestern U.S.
The southwest is where Krabbenhoft and her co-author, U.S. Geological Survey (USGS) biologist Jane Rogosch, PhD, first began researching fish living in dry (also known as xeric) climates. They were both undergraduates at the University of New Mexico in the 2000s.
Together with USGS ecologist Freya Rowland, PhD, they decided to review data spanning from 1980 to 2022 on intermittent and other streams in xeric climates throughout the U.S. and Australia.
“We know xeric regions are vulnerable to climate change, so we wanted to take a look at existing datasets related to their fish populations to see if anything stood out,” Krabbenhoft says.
Modeling the compiled data revealed increasing temperatures coinciding with declining precipitation. Rainwater decreased 0.137 millimeters per year in the U.S. and 0.083 millimeters per year in Australia.
In addition, the number of zero-flow days increased by about a half-day per year, while the maximum duration of no-flow periods increased by 0.62 days per year.
“This may not sound like a lot, but it’s actually a significant increase, especially when added up over the course of 42 years, and can have significant impact on an ecosystem,” Krabbenhoft says.
Reviewing 191 different species of xeric fish, they found a decline of about two species per stream in the U.S.; a lack of data prevented the team from being able to make a determination about Australia's fish diversity.
The most impacted xeric fish species tended to be smaller fish that eat plants, algae and other food sources more closely tied with streamflow.
“Additionally, a lot of the most impacted fish have a very small geographic range in the first place, so they’re very limited in where they can seek refuge when they're encountering reduced streamflow,” Krabbenhoft says.
Climate change just one piece of the puzzle
To the surprise of the researchers, their models could not confirm a direct connection between the drop in xeric fish species and the changes in their water availability. (Previous studies have found similar connections).
“This doesn't mean that climate change isn't an important piece of the puzzle, but it does mean it’s not the only piece of the puzzle,” Krabbenhoft says.
The researchers propose that multiple stressors are compounding to affect xeric fish populations, from invasive species to human development. Some of their streams have been restructured and channelized or become outflows for treated wastewater.
“Knowing that climate change is this vast, complex issue on a global scale, the least we can do is take a hard look at any additional stressors we may be putting on these ecosystems and see if there’s a way to give them some relief,” Krabbenhoft says.
The study's first author and co-corresponding author is Corey Krabbenhoft, assistant professor in the University at Buffalo Department of Biological Sciences.
Credit
Douglas Levere/University at Buffalo
Journal
Ecology and Evolution
Method of Research
Data/statistical analysis
Subject of Research
Animals
Article Title
Long-Term Regime Shifts in Xeric Ecoregion Freshwater Fish Assemblages due to Anthropogenic and Climate Stressors
Article Publication Date
17-Sep-2025
New study on fish reproduction suggests ongoing recovery of the Chicago River
At least 24 species of fish have been documented to breed in the Chicago River representing an incredible comeback for a once severely polluted river
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North Branch of the Chicago River
view moreCredit: Shedd Aquarium/Brenna Hernandez
A new peer-reviewed research paper, authored by Shedd Aquarium and published in Journal of Great Lakes Research, assesses the fish species that spawn in the Chicago River to sustain and support resilient, biodiverse fish populations. Utilizing light traps at 10 locations in the Chicago River between the years 2020 and 2022, over 2,000 larval fish were collected, and their DNA revealed 24 different fish species present.
“This research represents the first documentation of larvae from fish species occurring within the Chicago River, indicating that recovery and restoration efforts allow at least 24 species to successfully spawn and reach the larval stage,” said Dr. Austin Happel, author of the study and research biologist at Shedd Aquarium. “Our previous studies showed that improvements to water quality in the river increased biodiversity, and now we have more positive news as populations are proliferating locally within the river.”
Species that are reproducing in the Chicago River included popular sport fish such as black crappie, bluegill and largemouth bass, and forage fish such as gizzard shad, golden shiner and spotfin shiner. Further, the study uncovered larvae of brook silverside and mimic shiner, which are generally thought to be pollution-intolerant, and thus their presence was a pleasant surprise. The peak abundance of larvae occurred in July, coinciding with water reaching temperatures in the low 70s (degrees Fahrenheit).
The study showcased some differences across sites that could suggest additional opportunities to augment spawning habitats for fishes. Most notably, species considered intolerant of pollution were more common in the South Branch, yet species more tolerant to pollution were common in the North Branch of the Chicago River.
The finding suggests that some combination of suitable substrate, submerged vegetation, and water quality and flow are most likely present in the South Branch. Particularly, there’s a possibility of backwater areas, such as unused barge slips in Bubbly Creek, which serve as important nursery habitats and offer protection from predation and abundant food. Ongoing research by Happel focuses on how floating wetlands, which have been installed in the river by local nonprofit Urban Rivers and Shedd Aquarium over the last several years, affect successful fish reproduction.
“As people continue to care about and conserve this critical freshwater ecosystem, we hope to see increases in the number of fish spawning in the system,” said Dr. Happel.
Overall, the study offers hope for other heavily modified urban waterways and might offer insights on how to best support fish communities to spawn. Further, it demonstrates how restoration can work to bring wildlife back to local waters. This is important as healthy fish populations mean healthier aquatic environments, which ultimately benefits the people that live and work around them.
Shedd Aquarium works with partners and community members to reimagine, research and rewild the river. This ongoing effort involves creating new habitat with manmade floating wetlands, restoring existing habitat with volunteers, creating additional access through recreational opportunities, collecting data to monitor wildlife populations and more. Support for this work could include visiting the aquarium, volunteering for an action day, paddling for a good cause or donating to Shedd.
The findings from this research have been published in Journal of Great Lakes Research under the title, “Larval fish community of the urbanized Chicago River.”
Journal
Journal of Great Lakes Research
Subject of Research
Animals
Article Title
Larval fish community of the urbanized Chicago River
Article Publication Date
17-Sep-2025
