Overwintering Ability of Juvenile Ocean-Type Chinook Salmon: Effect of Water Temperature and Food Deprivation on Growth, Energetics and Survival

In ectothermic fishes, basic metabolism is driven by variability in the ambient water temperature, and thus influences bioenergetics. During winter, cool-water fishes can reduce metabolic demands by reducing activity level, but pelagic fishes like Chinook salmon continually swim to maintain position in the water column.  Our objectives were to evaluate the response of juvenile ocean-type Chinook to climate and food variability by controlling water temperature and food during winter and assessed overwinter survival, growth, basic metabolism and behavior.  Total survival was high (>85%) and similar between temperatures.  Fish in the low water temperature were larger than fish in the high temperature treatments.  Chinook from the high water temperature and deprived of food for four weeks suffered the greatest weight loss (1.0 % body weight day^-1).  Basic metabolism as measured by respiration rate was greatest in fish from the high temperature treatments.  Chinook subjected to the high water temperature were also more active and aggressive than fish from the low temperature.  The Northeast Pacific Ocean has been warming over the last several decades and warming winter ocean temperatures could negatively affect juvenile Chinook vital functions if food resources are not available or abundant enough to meet the increased physiological requirements.