Reintroducing Spring Chinook Salmon Above a High Head Dam in Oregon: Inference from Genetic Pedigree

Many fish species have been negatively affected by the construction of high head dams because they alter temperature and flow regimes, as well as, impede fish migration. In recent years, managers have begun to reintroduce salmonids above dams in an effort to mitigate these effects. This strategy has been adopted on the South Fork McKenzie River, Oregon. We investigated what factors explained reproductive success (RS) of adult spring Chinook salmon reintroduced from 2008-2011 using genetic parentage methods. We estimated RS by counting the number of outmigrating fry that assigned to an adult reintroduced in the previous year. Our analysis identified a small negative relationship (p<0.001) between Reintroduction Date and RS for males; however, Release Location was not associated with RS. We also investigated hatchery origin (HOR) and natural origin (NOR) RS differences in 2010-2011, and found that the interaction between Sex and Origin was significant (p<0.001). An interaction plot determined that mean RS of NOR males was higher than HOR males, but little difference was observed between HOR and NOR females. Our results suggest that releasing HOR females with NOR Chinook may aid in reintroduction efforts without negative consequences to juvenile production.