2004 Artic Yukon Kuskokwim Sustainable Salmon Initiative Project Final Report. Genetic Variation in Norton Sound Chum Salmon Populations

摘要

The genetic health of Norton Sound chum salmon populations may have been impacted by the regional-level decline in chum salmon abundance that began in the mid 1990s. However, limited genetic data exist with which to evaluate these populations. In this study, 20 microsatellite loci were used to describe and evaluate factors influencing intra and interpopulation genetic diversity in 15 populations from Norton and Kotzebue sounds. The microsatellite data provided evidence of statistically significant population structure within Norton Sound, overall and among ecoregions and fishing subdistricts, but not between every population pair. Despite their more rapid decline, chum salmon from the Nome Subdistrict exhibited levels of intra-population genetic diversity similar to those of other Norton Sound chum salmon. Early- and late-run chum salmon from Norton Sound exhibited levels of intra and interpopulation genetic diversity similar to those of chum salmon from the Yukon River. Genetic divergence was positively correlated with the geographic distance between early-run populations however, temporal isolation (early versus late run timing) was the largest single factor influencing population structure. Assignment test results suggested that the two late-run populations may differ in the extent to which their spawn timing overlaps with early-run populations. Estimates of effective population size (Ne) in four early-run populations were relatively large and were not indicative of a high risk of short-term loss of genetic diversity. Nevertheless, estimates of the immigration fraction (m) suggested that gene flow is a key determinant of genetic diversity in these populations and their long-term genetic health depends upon persistent gene flow, especially during declines in abundance. Estimates of the effective number of breeders per year (Nb) and the assignment test results suggested that gene flow is relatively balanced among most populations, and the genetic health of the early-run population complex depends upon maintaining connectivity among all populations. Finally, the collective results suggested that the Inmachuk and Koyuk River chum salmon populations are the most vulnerable to loss of genetic diversity should the decline in chum salmon abundance continue.