ABSTRACT
Variation in reproductive success (RS) among individuals within populations is an important determinant of effective population size (Ne), a critical component of the process of natural selection, and an important management issue in the case where non-native populations are introduced to supplement local native production. We are studying individual RS in three populations of winter-run steelhead trout (Oncorhynchus mykiss) in Washington State to shed light on all of these issues. One population is entirely wild, native and non-fished. The other two populations occur in a second drainage; one is wild and native, and the other is a recently established hatchery population of allopatric origin that has been selected to spawn earlier than wild populations to promote reproductive isolation between native wild and feral hatchery fish. We are non-lethally sampling pre-spawning adult steelhead in each of these populations, and their progeny at juvenile, smolt and adult life history stages. In each case we record phenotypic data (length, weight, time of upstream migration of adults) and take fin clips for DNA analysis. We are determining parentage, and hence realized reproductive success, through analysis of genetic variation in a suite of highly polymorphic microsatellite loci. Early results of this study will be discussed.