© by TERRAPUB 2008. Hatchery Stocking for Restoring Wild Populations: A Genetic Evaluation of the Reproductive Success of Hatchery

Potential impacts of hatchery programs on wild populations have long been discussed, and of particular interest is the reproductive success of hatchery-born fish in natural environments. Here I summarize our recent studies, in which DNA fingerprinting and genetic parentage analyses were used to esti-mate adult-to-adult reproductive fitness of steelhead trout (Oncorhynchus mykiss) in the Hood River, Oregon (USA). We found: (1) Hatchery fish left fewer adult offspring per parent than wild fish, but supplementation hatchery fish (from local, wild broodstock; Hsupp) left larger numbers of offspring than traditional hatchery fish (from nonlocal, multi-generation hatchery broodstock; Htrad); (2) The reproductive fitness of Hsupp declined unexpectedly fast (~40% per generation) when Hsupp were reused as broodstock in a hatchery, suggest-ing that the negative effects of hatchery rearing are cumulative and heritable; (3) Effective population size was mainly restricted by variance in reproductive success among individuals, rather than by biased sex ratio and temporal fluc-tuation of population sizes; (4) Htrad showed particularly large variance in re-productive success, indicating another negative effect of traditional programs. Our case studies suggest that using local, wild broodstock reduces negative effects of hatchery rearing, but the repeated use of Hsupp as broodstock should be minimized for efficient supplementation. KEYWORDS hatchery stocking; supplementation; effective population size; reproductive success; parentage analysis 154 H. ARAKI 1