Effects of Dam Altered Thermal Regimes on Development and Emergence Timing of Chinook Salmon Oncorhynchus tshawytscha

Due to thermal stratification in reservoirs, water released by dams is often a different temperature from environments further upstream on both daily and seasonal time scales. The impacts of flow regulation on temperature are important because of the influence that temperature has on development and distribution of species, especially salmon. Localized temperature regime changes caused by dams may spur local adaptation.  Furthermore, dam removal will change water temperature profiles downstream, which may transform selection patterns for populations that normally spawn below dams.  In a common garden laboratory incubation experiment, I measured emergence timing of fry from four Spring Chinook populations originating from Northwest river systems affected by hydropower dams. Each family of eggs was exposed to four different thermal regimes from fertilization to emergence to test the following hypotheses: 1) Altered temperature regimes can cause disparity in development timing between families and across populations.  2) Reaction norms for development timing under different temperature regimes are unique depending on family and population origin. 3) The condition of fry at emergence is regulated by an interaction between genotype and thermal regime. 4) The delivery method of temperature (constant vs. variable) affects emergence phenotypes. Results from this experiment will be discussed.