The Effects of Variable Water Temperature and Food Availability during Summer on Juvenile Chinook Salmon Early Marine Growth and Mortality

The objectives of this study were to experimentally evaluate how juvenile ocean-type Chinook salmon responded to climate and food variability during their first summer. Juvenile Chinook size was largest in the cool temperature treatments within the high and middle rations, and similar among low fed fish held at all three temperatures. Mortality of juvenile Chinook was highest in the hot temperature treatment (43%) and 96% of the total mortality of all fish in the first month occurred in hot water. Mortality was three to four times higher for fish inhabiting the warm and hot temperatures than cool water fish fed at the middle and high rations. Size-selective mortality of juvenile Chinook salmon in the cool temperature treatment was consistent across all three feeding regimes, yet variable in the warm and hot water treatments. Summer SSTs approaching those simulated in the warm and hot temperature treatments of this study could have a negative impact on natural populations of ocean-type Chinook salmon resulting from stunted growth and increased mortality during the early marine phase even when food is abundant.