Alex Baumhardt

(Oregon Capital Chronicle) In Sept. 2020, the Archie Creek fire near Roseburg burned all 5,000 acres of the Hinkle Creek watershed, home to rainbow, cutthroat and steelhead trout.

Oregon State University scientists who had been studying the fish for years figured the loss of tree cover would mean warmer stream temperatures that would stress, and ultimately kill, many of the fish.

Instead, the researchers found that by the end of the summer the following year, trout populations were not only unimpacted but had grown in some areas.

“The fish in this system proved to be quite resilient to these increased temperatures – at least within the range that we saw here,” lead researcher Dana Warren said in a news release.

Warren and three co-authors from OSU’s Department of Fisheries and Wildlife and the College of Forestry published the findings in the journal Ecosphere in September. The scientists suggest that this could bode well for the ability of trout species to survive the ongoing impacts of climate change, including more frequent and larger wildfires, and warmer water temperatures.

Abrupt changes to an ecosystem, such as fire, can provide key insights into how fish species are immediately impacted by rising temperatures and how they respond to such dramatic changes to their ecosystems.

Prior to the fire, the fish had been living in water temperatures that averaged 59 degrees Fahrenheit. Afterward, during the summer of 2021, they were surviving in temperatures about 7 degrees warmer on average, and at times in water that soared as high as 77 degrees Fahrenheit – warmer than they had ever experienced.

The researchers noted that because most of the aquatic species in the watershed are cold-water species, the trout did not face competition from warm-water species that might have had increased their populations or had greater access to food in the higher temperatures. That could be a bigger issue in watersheds where there is a greater mix of both cold- and warm-water fish.

Other factors could also be helping the trout to survive warmer waters, according to the scientists. Periodically, cold groundwater discharges might have helped the fish cool off, they said. They also might have been able to recover from the day’s heat at night when temperatures dropped. It’s also possible there was increased food availability during the summer, according to the report.

Researchers need to conduct further studies, Warren said in the news release. They plan to study other fish and amphibians in the watershed, as well, including the coastal giant salamander and sculpin.

The scientists have enough funding to continue studying the watershed for at least another four years.