This project addresses a key uncertainty for evaluating whether hatchery supplementation programs have a net positive contribution to recovery of listed populations. Specifically, what is the relative reproductive success of naturally spawning hatchery fish and what are causes of poor reproductive success of hatchery fish? We are addressing these questions by focusing on the spring Chinook salmon in the Wenatchee River, part of the endangered Upper Columbia River spring Chinook salmon ESU. Our study design uses genetic parentage analysis to assign progeny (sampled at both the smolt and adult life stages) to naturally spawning hatchery and wild origin fish. The progeny counts for each spawner are a measure of reproductive success, and by comparing the mean reproductive success of hatchery and wild spawners, we obtain an estimate of the relative reproductive success (RRS) of the hatchery origin fish. A key part of the study is to include co-variables, such as age, size, run timing, spawning location, and spawning behavior, in the analysis so that the proximate causes of differences in RRS between hatchery and wild fish can be evaluated. The study was initiated in 2004, and we have sampled 10 years of adults and 8 years of smolts. In several papers and reports generated by this project, we have reported on the RRS of spawners sampled in 2004-2007, and 2010, and have found that spawning age, size, and location, in addition to hatchery/wild origin, are important co-factors explaining variation in reproductive success. This has been a highly influential study that addresses a critical uncertainty identified in both recovery plans and biological opinions and has had strong support from the West Coast Regional Office. Microsatellite data from spring run Wenatchee River Chinook salmon.