2004 Artic Yukon Kuskokwim Sustainable Salmon Initiative Project Final Report. Effective Population Size of Chinook Salmon in Yukon and Kuskokwim River Tributaries

摘要

The effective population size per generation (Ne) is an important indicator of the genetic health and viability of a population. In this study, genetic and demographic data are used to estimate and evaluate contemporary Ne for Chinook salmon (Oncorhynchus tshawytscha) from the Gisasa and Tozitna rivers, tributaries of the Yukon River, and the Kwethluk and Tuluksak rivers, tributaries of the Kuskokwim River. The genetic estimates of Ne range from 2,307 to 7,674 when the populations are assumed to be isolated, but are much smaller when migration is assumed, ranging from 448 to 576. Estimates of the immigration fraction per generation (m) vary considerably, ranging from 0.07 to 0.09 for the Yukon River populations and 0.34 to 0.43 for the Kuskokwim River populations. The mean genetic estimate of the ratio Ne to census size (N) is 0.28, assuming isolation, and 0.04, assuming migration. The estimates of Ne/N vary widely among populations but clearly show that census size estimates are not accurate indicators of genetic health. A comparison of Ne/N ratios from genetic and demographic data suggests Ne is impacted most by unequal sex ratio and variance in reproductive success and least by fluctuating population size for the time period examined in this study. The results indicate the observed sex ratio bias could adversely impact the long term genetic health of these populations if annual run sizes, and migration rates, decline. Further, the results underscore the importance of maintaining population connectivity and suggest that the vulnerability to loss of genetic diversity varies regionally and is negatively correlated with gene flow.