The Variable Family Response of Emergence Timing for Spring Chinook Salmon Eggs Incubated Under Different Thermal Regimes

Life history strategies related to spawn timing are known to vary among, and occasionally within, different salmonid species.  An example of this is demonstrated by Chinook salmon that may be classified as either Spring or Fall run-type, depending on the season in which the mature adults return to freshwater to spawn.  Furthermore, variation in spawn timing within an ecotype of salmon is also well documented, thus, the interaction between genetics and environment is not a novel idea. We set out to investigate this interaction on a smaller scale at the family level.  A laboratory experiment was conducted in the research hatchery of the Northwest Fisheries Science Center, Seattle using fertilized eggs from eight separate families of Yakima River Spring Chinook salmon that were artificially spawned on the same day at the Cle Elum Hatchery, WA.  Each family was further divided into eight equal groups, and each group incubated under a different thermal regime, resulting in an 8 X 8 matrix of treatment groups (family by thermal regime).  Results indicate that the interaction between genetics and environment was significant at the family level, based on differences in emergence timing.  This implies that the classic "degree-day model" currently used to predict emergence timing is not precise with regard to family level differences.  This is an important consideration as resource managers endeavor to evaluate the effects of the increasing complexity in thermal variation that hydroelectric dams and climate change add to localized environments of Chinook salmon populations.