Population structure and stock identification of steelhead trout (Oncorhynchus mykiss) in British Columbia and the Columbia River based on microsatellite variation

Variation at 13 microsatellite loci was surveyed from similar to 3 800 steelhead trout, Oncorhynchus mykiss, from 51 populations in British Columbia, Washington, and the Columbia River drainage. Mean F-ST over all 13 loci and 51 populations was 0.066. Regional structuring of populations was apparent, with Thompson River, upper Fraser River, and Columbia River populations forming distinct groups. In the Nass River, winter-run populations were distinct from the summer-run populations. Significant differences in allele frequencies were observed among regional stock groups at all loci. Analysis of variance components indicated that 5.7% of the total observed variation was distributed among 11 regions, and 2.3% of the variation was among populations within regions. Analysis of simulated mixed-stock samples suggested that variation at the microsatellite loci provided relatively accurate and precise estimates of stock composition for fishery management applications, and this was confirmed by application to actual fishery samples of known origin. Within the Fraser River drainage, individual steelhead trout can be identified to one of the three regions of origin with an accuracy of 94 - 97%. Microsatellites provided an effective way to determine population structure, and provided reliable estimates of stock composition in mixed-stock fisheries.