Recent studies from the University of British Columbia found that salmon, specifically younger salmon in the province, are more vulnerable to rising temperatures than previously measured. The data were collected through two separate but related research projects, both of which aimed to determine the risks salmon face in warming rivers. Dr. Scott G. Hinch is a featured researcher on the project and said, in a UBC release, that his team worked with Fisheries and Oceans Canada and the National Institute of Aquatic Resources in Denmark to analyze two- and six-month-old salmon, referred to as fry and parr respectively, in B.C.’s Nicola River. “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,” he said. “We also considered how age and prior temperature exposures influence responses.” Hinch said research showed these juvenile fish had a harder time swimming in warmer temperatures than when stationary, which he explains suggests “traditional tests may overestimate their heat tolerance” when they’re swimming in natural conditions. “We identified 20 C as an important threshold. Fish acclimated to this temperature or warmer performed better up to that point, but beyond it, their ability to cope declined,” he said, in a release. “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.” On the other hand, Hinch said the fish acclimated to temperatures in the 12 to 15 C range would die shortly after swimming in water that was 24 C, which he said suggests their “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,” he said. Rapid heat events don’t happen all the time, but this week marked the fifth anniversary of a heat dome event that saw Lytton, B.C., set a record for the highest temperature recorded in Canada, at 46 C, and killed hundreds of people as temperatures soared province-wide, according to a release from the Canadian Association of Physicians for the Environment. Hinch said heat stress has different effects on salmon based on their respective life cycle stages, and stressed the importance of that being considered in conservation and management strategies. He explained that this can be done by reducing thermal stressors when B.C. reaches its highest temperatures, further outlining that this can be done by “maintaining and protecting riparian trees and groundwater sources to help keep waterways cool,” among other methods. Looking at 2026 salmon returns, Hinch said, “food-rich coastal waters linked to La Niña conditions” may yield similar results to 2025, which saw strong numbers on sockeye and pink salmon, according to data from the Pacific Salmon Foundation. Hinch adds that temperatures brought by the current El Niño conditions could cause issues for returning adult salmon as they find their way through B.C.’s rivers, facing drought and warm temperatures. On young salmon who will spend another year or two in fresh water, like the fry and parr analyzed in these two studies, Hinch said their “situation is more concerning.” “A ‘super’ El Niño is projected to bring warm coastal waters, poor food availability and abundant predators, and a large blob of warm ocean water is also approaching our coast, reflecting cumulative climate change impacts,” he said.
