Population structure and stock identification of steelhead in southern British Columbia, Washington, and the Columbia river based on microsatellite DNA variation

The purpose of this study was to describe population structure and determin e the potential for genetic stock identification for steelhead Oncorhynchus mykiss in British Columbia using microsatellite DNA markers. Variation at eight microsatellite DNA loci (Oki200, Omy77, Ots1, Ots3, Ssa85, Ots100, Ot s103, and Ots108) was surveyed in approximately 1,500 steelhead from 22 pop ulations in southern British Columbia, Washington, and the Columbia River d rainage as well as in more than 450 steelhead from two commercial salmon fi sheries conducted off the southwest coast of Vancouver Island. Nine populat ions were sampled for two or more years, and variation in allele frequencie s among populations and regions was, on average, about 3.7 times greater th an annual variation within populations. Regional structuring of populations was apparent, with Thompson River, upper Fraser River, and Columbia River populations forming distinct groups. Significant differences in allele freq uencies were observed among regional stock groups at all loci. After variat ion within populations was accounted for, variation among regions was the g reatest source of the remaining variation (4.4%), followed by variation amo ng populations within regions (3.1%) and variation among years within popul ations (2.0%). The overall classification accuracy of single individuals to five regional groups using a jackknifed discriminant analysis was 80%. Sim ulated mixed-stock samples suggested that variation at the eight microsatel lite DNA loci surveyed should provide relatively accurate and precise estim ates of stock composition for fishery management applications. Analyses of commercial marine fisheries samples indicated that during 1994-1996 more th an 85% of the steelhead sampled in a directed chum salmon fishery off the m outh of the Nitinat River originated in the Eraser River drainage with the majority of steelhead from the Thompson River. However, in 1997, steelhead of U.S. origin were estimated to have composed 60% of the samples, and the Canadian component was largely of Eraser River steelhead, possibly reflecti ng anomalies associated with climatic variation. Estimated stock compositio n of samples from the 1997 sockeye salmon fishery in Barkley Sound indicate d that the majority (71%) of steelhead was of Vancouver Island origin with the remainder being of U.S. origin.