Conservation Hatcheries and Small Populations: Effects on Abernathy Creek Steelhead

One of the most important goals of conservation supplementation programs for small or imperiled populations is the maintenance of genetic variability while increasing population size.  Many such hatchery programs rely on an integrated broodstock which incorporates a high proportion of natural origin adults into hatchery families, and allows hatchery adults to spawn in the wild with the natural population.  These programs attempt to limit divergence between hatchery and wild fish, while also increasing the size of the naturally spawning population, and their success can be greatly affected by broodstock selection protocols and the reproductive success of hatchery fish in the wild.  Recent studies of such practices in steelhead and other species have revealed that loss of genetic variation is a common problem in hatchery populations, and that reproductive success of hatchery fish spawning in the wild is generally lower than their wild counterparts.  The supplementation program for Abernathy Creek steelhead in the Lower Columbia River was initiated in 2004 with the intent to create an integrated hatchery program which increased the number of steelhead returning to the system while minimizing the negative impacts of hatchery supplementation.  Here we present data showing that the integrated broodstock produced at the USFWS Abernathy Fish Technology Center appears to have experienced a decrease in genetic variation and an increase in family structure since the hatchery was initiated.  Although the number of adults returning to the creek has increased in the past three years, the broodstock shows significant divergence from the wild population and high variability in allele frequencies among years.  In addition, preliminary findings indicate that reproductive success of hatchery fish spawning naturally in Abernathy Creek has been highly variable among years relative to wild fish.  We discuss how variation in the number of hatchery families and the proportion of natural and hatchery origin adults in both the broodstock and on the spawning grounds among years play an important role in determining the genetic impacts of the hatchery on the wild population.