Impacts and Implications of Temperature Variability on Chinook Salmon Egg Development and Emergence Phenology

The nonlinear relationship of egg development rates to temperature due to compensatory mechanisms in Chinook Salmon Oncorhynchus tshawytscha has consequences for emergence timing in nonoptimal and/or highly variable temperature regimes. A mechanistic model of the relationship between temperature and development was used to better understand laboratory results on the primary effects of temperature variability leading to emergence. The model was then applied to a natural river system and used to predict emergence timing while considering additional factors associated with natural spawning such as an individual spawner's timing, the stock's spawning season, and spawning cue. In the natural system simulations, the largest source of emergence timing variability was due to interannual water temperature regimes and spawning date variation. Lesser emergence variability resulted from temperature variability, family lineage, egg size, individual spawner's timing, and spawning cue. An improved understanding of the role of riverine thermal regimes in inducing developmental variability can contribute to conservation planning and predictions of phenology under future climates.