Effects of high water temperature on growth, smoltification, and predator avoidance in Juvenile Sacramento River Chinook salmon

Intensive water management and frequent drought cycles can increase water temperatures, thereby decreasing habitat quality for Chinook salmon Oncorhynchus tshawytscha inhabiting streams of California's Central Valley. We studied the incremental effects of chronic exposure (>60 d; effects measured bimonthly) to three temperature regimes typical of the range of conditions experienced by Sacramento River fall-run Chinook salmon during juvenile rearing and smoltification (13-16degreesC, 17-20degreesC, and 21-24degreesC; diel fluctuations of 0.5-3degreesC were allowed within these limits). Our laboratory experiments demonstrated that Chinook salmon can readily survive and grow at temperatures up to 24degreesC. However, juveniles reared at 21-24degreesC experienced significantly decreased growth rates, impaired smoltification indices, and increased predation vulnerability compared with juveniles reared at 13-16degreesC. Fish reared at 17-20degreesC experienced similar growth, variable smoltification impairment, and higher predation vulnerability compared with fish reared at 13-16degreesC. These results improve our understanding of the range of juvenile Chinook salmon responses to elevated temperatures and should assist biologists and resource decision makers in coordinating water management and salmon conservation decisions.