Selection Gradients Associated with Reproductive Success of Hatchery- and Natural-Origin Chinook Salmon in the Grande Ronde Basin (Northeast Oregon)

Hatchery supplementation programs are designed to increase natural production, but the success of these programs can be difficult to evaluate.   A census of hatchery- and natural-origin fish returning to spawn allows for comparisons of ocean survival, but a primary goal of many supplementation programs is to produce hatchery-origin fish that are, in all ecologically significant ways, equal to their natural counterparts:  age and timing of smolt migration, return timing, size and age at return, spawning location, number of mates, number of offspring produced, etc.  We used pedigree analysis to measure relative reproductive success of hatchery and natural Chinook spawning in nature in Catherine Creek (Grande Ronde River), evaluated at multiple life stages:  precocial parr, parr, migrants, and returning adults.  The resulting pedigrees allowed us to compare relative reproductive success as well as differences in the ecological characteristics listed above.  Initial results in Catherine Creek do not show a significant decrease in reproductive success of hatchery-reared fish compared with their natural counterparts, although there is substantial variation among years and life stages.  This is very different from the significant reduced reproductive success we have documented in steelhead in the neighboring Imnaha River system.  The Catherine Creek program was established more recently than the steelhead program, and perhaps time-in-culture plays a role in their differences.  Alternatively, Chinook salmon might be more resilient to hatchery rearing than steelhead.  The processes that drive differential reproductive success remain problematical.  We continue monitoring these systems to document the genetic and demographic effects of supplementation and to better understand the drivers of differential fitness among families and classes of parents.