• coregonine;
  • dispersal;
  • Mackenzie River system

In this study, the magnitude and direction of gene flow and estimates of effective population sizes (Ne) were quantified among two life-history types (lacustrine and anadromous) of broad whitefish Coregonus nasus in the lower Mackenzie River system. The data suggest that dispersal and subsequent gene flow occurs between these groups, with the former appearing to be asymmetrical. Gene flow may potentially be directionally biased as well, a result attributed to source–sink population dynamics and the ongoing process of post-glacial colonization and contemporary range expansion. Additionally, average Ne estimates were consistently lower for lacustrine populations of C. nasus although confidence intervals for both contemporary and historical estimates broadly overlapped. The lower average estimates of Ne for lacustrine populations was suggested to be the result of more recent founding events following post-glacial dispersal. This study provides one of the first assessments of gene flow and Ne in an Arctic coregonine, results that may be relevant to other freshwater and anadromous Arctic species persisting in systems near the periphery of their range.