Parental Effect as a Primary Factor Limiting Egg‐to‐Fry Survival of Spring Chinook Salmon in the Upper Yakima River Basin

Abstract

AbstractFew field estimates of egg‐to‐fry survival of Chinook salmon Oncorhynchus tshawytscha exist, although it is one of the major factors thought to limit freshwater production and recovery of Chinook salmon populations. This is likely due to the challenges of estimating survival at this life stage, which is further complicated by the variety of methods that have been employed. Our study objectives were to (1) develop a method by which spring Chinook salmon egg‐to‐fry survival could be estimated at a large spatial scale, and (2) investigate the primary factors affecting survival in the natural environment. We conducted a field experiment using 81 artificial redds to test our proposed method for evaluating egg‐to‐fry survival at a basin scale and to evaluate the effects of parentage (adult mating), river reach, and fine sediment infiltration on survival in the upper Yakima River basin, Washington. Egg‐to‐fry survival and preemergent Chinook salmon fry developmental stage were significantly different among matings, but were not detectably different among reaches. Fine sediment accumulation in egg boxes from artificial redds was largely below published threshold levels, explained less than 6% of the variation in survival, and was not correlated with developmental stage. In contrast, survival of individual matings in the natural environment and those same matings incubated under controlled hatchery conditions were highly correlated. Our study suggests that in years of low scour and potentially ideal incubation conditions, parental effects play an important role in determining in situ egg‐to‐fry survival, and that extensive replication and tracking of gamete viability is needed to separate parental effects from environmental factors affecting survival. We provide standardized methods for collecting egg‐to‐fry survival data and outline a number of potential biases that should be addressed in future research.