Estimation of Genetic Diversity within and among Populations of Oncorhynchus mykiss in a Coastal River Experiencing Spatially Variable Hatchery Augmentation

Abstract

AbstractThe allelic variation at 10 microsatellite loci was assayed in potentially wild rainbow trout Oncorhynchus mykiss and steelhead (anadromous rainbow trout) collected from 11 tributaries and three upper main‐stem river sites (n = 547) in the Kitimat River, central British Columbia, and compared with the variation in steelhead from areas within the lower river (n = 333), where a hatchery has operated since 1984. The objective was to see whether the genetic structure of O. mykiss in the upper river was influenced by hatchery‐reared fish stocked in the lower river. Measures of genetic diversity indicated that tributary and upper‐river diversity were similar to what has previously been documented for wild populations. The level of genetic subdivision (θ) was significant (θ = 0.031), indicating that genetic structure exists, and was higher than that among sites located in the lower main‐stem river where the hatchery operates (θ = 0.004). Bayesian assignment clustering suggested the existence of a genetic structure (K = 3) in O. mykiss in the upper river. The overall spatial pattern, however, identified no clearly separate genetic populations; rather, the genetic structure appeared to be an overlapping mosaic of modestly genetically divergent localities. We conclude that indigenous wild O. mykiss populations exist in the tributaries and the upper main‐stem river and its tributaries. These upper‐river populations appear to have retained genetic diversity and differentiation despite extensive releases of hatchery fish in the lower river.