‘A canary in the coal mine’: Even fish adapted to dry climates are struggling amid rising temps, droughts

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.