Population structure and conservation genetics of anadromous white-spotted char (Salvelinus leucomaenis) on Hokkaido Island: Detection of isolation-by-distance

To increase the quantity of anadromous and freshwater fish resources and conserve natural populations effectively, it is important to identify conservation units and population structures, as well as to ensure sufficient genetic variability within populations. Here, we used 12 microsatellite loci to evaluate the population structure, effective population size, and bottlenecks in seven anadromous white-spotted char (Salvelinus leucomaenis leucomaenis) populations inhabiting the rivers of Hokkaido Island, Japan. Low migration rates were detected among populations, with significant genetic differentiation being observed, suggesting high homing rates. In addition, isolation-by-distance was observed among the evaluated populations, indicating that the populations in this region are at equilibrium between migration and drift. We identified a genetic bottleneck footprint in all seven of the analyzed white-spotted char populations by using the M ratio test. In contrast, heterozygote excess tests showed that all seven populations showed no signatures of population decline. This discrepancy may have been caused by differences in statistical power among tests. Alternatively, this discrepancy may be consistent with a strong founder effect during the late Pleistocene, followed by a subsequent low migration rate among populations. In conclusion, future conservation genetic management strategies should ensure that anadromous white-spotted char populations successfully exhibit homing behavior in the rivers of Hokkaido Island, Japan.