Ecological and Genetic Effects of a Conservation Hatchery on Natural-Origin Steelhead: Lessons from a Decade-Long Study in Abernathy Creek, Washington

Hatcheries have long been used for supplementation of threatened and endangered Pacific salmon (Oncorhynchus spp.) in the Pacific Northwest, though traditional hatchery practices can pose ecological and genetic risks to local salmon populations.  Our goal was to test whether proposed conservation hatchery techniques such as developing local broodstocks and maintaining integration between hatchery-origin (HOR) and natural-origin (NOR) populations could minimize negative ecological and genetic impacts of a hatchery program to a steelhead (O. mykiss) population.  A local broodstock was obtained by rearing captured age 0+ NOR juveniles to sexual maturity, and the HOR population has been integrated with the NOR population since 2003.  Hatchery supplementation has successfully increased the abundance of HOR steelhead in Abernathy Creek, while the results for adult and juvenile NOR steelhead abundance in the creek have been mixed.  Morphological and physiological differences persist between HOR and NOR steelhead at various life history stages.  The HOR population showed genetic divergence from the NOR population, a reduction in the effective number of breeders, and an increase in temporal population structure.  These differences suggest that the implementation of these conservation hatchery techniques has not been sufficient to alleviate the ecological and genetic risks associated with supplementation in this population.