The geographic basis for population structure in Fraser River chinook salmon

• Published in: Fishery bulletin (Washington, D.C.) Vol. 101; no. 2; pp. 229 - 242
• Main Authors: Beacham, Terry D, Supernault, K. Janine, Wetklo, Michael, Deagle, Bruce, Labaree, Karen, Irvine, James R, Candy, John R, Miller, Kristina M, Nelson, R. John, Withler, Ruth E
• Format: Journal Article
• Language: English
• Published: National Marine Fisheries Service 01.04.2003
• Subjects: Chinook salmon; Fish populations; Freshwater; Genetic aspects; Oncorhynchus tshawytscha; British Columbia; Canada, British Columbia, Thompson R; Canada, British Columbia, Fraser R; Canada, British Columbia, Birkenhead R
• ISSN: 0090-0656; 1937-4518

We surveyed variation at 13 microsatellite loci in approximately 7400 chinook salmon sampled from 52 spawning sites in the Fraser River drainage during 1988-98 to examine the spatial and temporal basis of population structure in the watershed. Genetically discrete chinook salmon populations were associated with almost all spawning sites, although gene flow within some tributaries prevented or limited differentiation among spawning groups. The mean F sub(ST) value over 52 samples and 13 loci surveyed was 0.039. Geographic structuring of populations was apparent: distinct groups were identified in the upper, middle, and lower Fraser River regions, and the north, south, and lower Thompson River regions. The geographically and temporally isolated Birkenhead River population of the lower Fraser region was sufficiently genetically distinctive to be treated as a separate region in a hierarchial analysis of gene diversity. Approximately 95% of genetic variation was contained within populations, and the remainder was accounted for by differentiation among regions (3.1%), among populations within regions (1.3%), and among years within populations (0.5%). Analysis of allelic diversity and private alleles did not support the suggestion that genetically distinctive populations of chinook salmon in the south Thompson were the result of postglacial hybridization of ocean-type and stream-type chinook in the Fraser River drainage. However, the relatively small amount of differentiation among Fraser River chinook salmon populations supports the suggestion that gene flow among genetically distinct groups of postglacial colonizing groups of chinook salmon has occurred, possibly prior to colonization of the Fraser River drainage.