The Cost of Living in a Warming World: Physiological and Behavioral Response of Juvenile Chinook Salmon to Simulated Seasonal Water Temperature

Rising temperatures in the Northeast Pacific Ocean over the past 30+ years have been associated with declines in the early marine survival of many southern British Columbia populations of Chinook salmon, but the mechanisms are unclear.  Our objectives were to experimentally evaluate the effects of variable seasonal water temperature on juvenile ocean-type Chinook salmon blood cortisol levels, basic metabolism, and behavior. Summer blood plasma cortisol concentration (ng/ml) of juvenile Chinook increased with increasing water temperature from 15°C (19.1 ng/ml) to 21°C (58.7 ng/ml), exceeding the known unstressed levels (~ 40 ng/ml) in Chinook salmon.  Water temperatures were reduced in autumn, and the cortisol levels of Chinook were similar across temperature treatments by the end of this season.  The respiration rate of fish also increased with temperature, and was higher during the summer than autumn across water temperatures.  Overall fish activity was similar across treatments during the summer, while aggression varied among water temperatures, and both behavioral metrics decreased during autumn.  In summary, juvenile Chinook salmon inhabiting natural systems that encounter environmental conditions similar to those simulated in this study, particularly during summer, could suffer negative impacts to physiology resulting from increased stress and metabolic demands, as well as altered behavior.