Genetic monitoring informs conservation status and trend of Arctic grayling at the southern edge of their distribution

The number of effective breeders (N-b) has been touted as a means to monitor freshwater fishes, but the realized application of N-b has been limited. Using genetic monitoring data for two Arctic grayling (Thymailus arcticus) populations of conservation concern, we describe temporal trends in genetic variation and N-b, determine how sampling and variance in reproductive success influence estimates of N-b, and quantify the relationship among N-b, effective population size (N-e), and adult abundance (N-e). Temporal trends in allelic richness (A(R)) and N-b tracked known or suspected population trajectories. N-b increased in one population where there has been extensive conservation action, and both N-b and A(R) tracked a decline in the other population where harsh winter conditions have resulted in overwinter mortality events. After accounting for population demography, N-e estimates for each population were 190.7 and 308.8. Overall, this study demonstrates that temporal genetic data effectively resolve demographic and evolutionary status and trend in Arctic grayling, provides insight into the demographic factors that influence genetic variation, and emphasizes the value of temporal genetic data for conservation and management.