Evaluation of Woundfin Augmentation Efforts in the Virgin River by Estimation of Admixture Proportions

The woundfin Plagopterus argentissimus is imperiled as a result of habitat destruction, water diversion, and the introduction of nonnative species. Augmentation of wild woundfin populations in the Utah portion of the Virgin River with fish from Dexter National Fish Hatchery and Technology Center (Dexter Hatchery) began in 2003. We used 10 microsatellite DNA loci to determine whether captive woundfins are contributing to recruitment in the Virgin River. Admixture analyses based on moment estimators, maximum likelihood, frequency, and Bayesian approaches indicated that the genetic contribution of Dexter Hatchery's woundfin augmentation stocking to 2005 recruitment in the Virgin River was 35-46% in the Washington Fields Diversion reach and 43-59% in the area of the Quail Creek Reservoir inflow. Salvaged wild parental stock was mixed with the captive broodstock at Dexter Hatchery in 2004 and had a genetic contribution of 26-49% to the offspring reared at Dexter Hatchery in 2005. Care must be taken to ensure the genetic integrity of stocked fish as the potential impact on the augmented population can be substantial. These results demonstrate that genetic markers used to infer gene flow (via admixture analysis) from the captive population to the wild population can be applied to determine the effectiveness of hatchery propagation programs and to monitor genetic similarity between wild and stocked fish.