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 (Thymallus 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_c). 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.