A Year in the (Early Marine) Life of Chinook Salmon: Effects of Variable Water Temperature and Food Availability on Seasonal Growth, Condition and Mortality

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 how juvenile ocean-type Chinook responded to temperature and food variability during their first summer, autumn and winter.  Water temperature had a greater effect on growth than energetics, such that the growth potential of fish was maximized in the lowest water temperature during summer and highest temperature during winter, while lipid content was primarily influenced by ration in all seasons except for summer.  Seasonal mortality was greatest during summer, particularly at the highest water temperature (45%).  Only 20% of fish died during winter, even when completely deprived of food.  Summer ocean temperatures approaching those simulated in the highest temperature here could negatively affect natural populations of Chinook salmon resulting from stunted growth, poor condition and increased temperature-induced acute mortality even when food is abundant. The compensatory growth response and energy maintenance during winter by fish that survived the highest summer temperature suggests that the effects of climate change on juvenile Chinook salmon physiology may only be critical during summer.