Patterns of intra- and inter-population genetic diversity in Alaskan coho salmon: Implications for conservation

Abstract

Little is known about the genetic diversityof coho salmon in Alaska, although this arearepresents half of the species' North Americanrange. In this study, nine microsatellite lociwere used to genotype 32 putative coho salmonpopulations from seven regions of Alaska. Theprimary objectives were to estimate andevaluate the degree and spatial distribution ofneutral genetic diversity within and amongpopulations of Alaskan coho salmon. Geneticanalysis yielded four results that provideinsight into forces influencing geneticdiversity in Alaskan coho salmon and haveimportant conservation implications: 1)significant population differentiation wasfound within each region; 2) the degree ofdifferentiation (FST = 0.099) amongpopulations was as large or larger than thatreported for other Pacific salmon species inAlaska; 3) phenetic clustering of populationsshowed weak geographic concordance; 4) stronggenetic isolation by distance was only apparentat the finest geographic scale (within adrainage). These results suggest that cohosalmon populations are small relative topopulations of other Pacific salmon, and thegenetic diversity within and among coho salmonpopulations is influenced primarily by geneticdrift, and not gene flow. Resource managementand conservation actions affecting coho salmonin Alaska must recognize that the populationsare generally small, isolated, and probablyexhibit local adaptation to different spawningand freshwater rearing habitats. These factorsjustify managing and conserving Alaskan cohosalmon at a fine geographic scale.