Wednesday July 1, 2026
phys.org —
As climate change warms rivers across British Columbia, young salmon are facing increasing heat stress at vulnerable stages of their lives. Two studies from UBC’s Pacific Salmon Ecology and Conservation Lab have found that younger fish cope with heat differently than older fish and that current methods may be underestimating the risks salmon face in warming waterways.
In this interview, Dr. Scott Hinch, professor in UBC’s faculty of forestry and environmental stewardship, talks about what these findings mean for salmon conservation.
What did you investigate?
We examined how young salmon respond to warming water and whether current methods accurately measure heat tolerance. Most studies assess fish at rest, but juvenile salmon are constantly moving to find food and avoid predators, so we need to mimic real-world conditions. We also considered how age and prior temperature exposures influence responses.
Collaborating with researchers from Fisheries and Oceans Canada and the National Institute of Aquatic Resources in Denmark, we studied juvenile Chinook salmon from the Nicola River in B.C. We compared two life stages: fry, about two months old, and parr, around six months old. One study, published in the Journal of Experimental Biology, explored the biological mechanisms that influence heat tolerance, while a second study, accepted in Conservation Physiology, examined swimming performance and survival at different temperatures.
What did you find?
When monitored while swimming, fish were less able to physiologically cope with warm temperatures than they could in stationary trials, suggesting that traditional tests may overestimate their heat tolerance in natural conditions.
We identified 20° C (68° F) as an important threshold. Fish acclimated to this temperature or warmer performed better up to that point, but beyond that, their ability to cope declined.
Surprisingly, fry handled warmer temperatures better than parr, tolerating about 1.8°C higher on average. We think older fish may struggle to pump enough oxygen-rich blood to their muscles as temperatures rise.
Fish that were acclimated to cooler temperatures like 12 to 15° C, but swam vigorously at 24° C (75° F), died shortly after the trials, suggesting an inability to recover from a single rapid heat event. A juvenile salmon living in a cool river that encounters really warm temperatures may not survive such a rapid temperature change.