EPA funded an investigation of Chinook salmon temperature tolerance to contribute to available knowledge about the effects of temperature on California Chinook salmon. This investigation uses aerobic capacity as a measure of performance in response to a range of environmentally relevant temperatures in laboratory conditions. The following list summarizes key observations from the final report, Thermal performance in Juvenile Hatchery Oncorhynchus tshawytscha: Aerobic Scope over a Range of Environmental Temperatures.

• Juvenile Chinook salmon in the laboratory were able to maintain physiological performance from 12 to 25°C
• Mortality rates abruptly increased at 25°C
• The metabolic performance of hatchery fish measured in this laboratory study under stable habitat and food supply conditions may vary substantially from the metabolic performance of wild fish in their actual habitat which includes variable oxygen levels and food availability and the increased metabolic costs of predator avoidance, foraging, and finding optimal habitat

Additional research on Central Valley Chinook salmon should be done to improve our understanding of how temperature affects survival.  The upper limit of thermal tolerance of hatchery fish in laboratory conditions measured by aerobic scope in this study is considerably higher than recommended temperature criteria of 16 – 18 °C for rearing and migration of juvenile salmon in the wild. Future studies should include more measurements such as heart rate, growth, and swimming performance and evaluate juvenile salmonids from different populations in their environment to measure effects in wild populations of fish.

• Thermal Performance in Juvenile Hatchery Oncorhynchus tshawytscha: Aerobic Scope Tests Over a Range of Environmental Temperatures (PDF)(29 pp, 610 K, March 15, 2016)