Data from: Long-term evaluation of fitness and demographic effects of a Chinook salmon supplementation program

While the goal of supplementation programs is to provide positive, population-level effects for species of conservation concern, these programs can also present an inherent fitness risk when captive-born individuals are fully integrated into the natural population. In order to evaluate the long-term effects of a supplementation program and estimate the demographic and phenotypic factors influencing the fitness of a threatened population of Chinook salmon (Oncorhynchus tshawytscha), we genotyped tissue samples spanning a 19-year period (1998-2016) to generate pedigrees from adult fish returning to Johnson Creek, Idaho USA. We expanded upon previous estimates of relative reproductive success (RRS) to include two full generations and used generalized linear models to determine if origin (hatchery or natural) or phenotypic traits (timing of arrival to spawning grounds, body length, and age) significantly predicted reproductive success (RS) across multiple years. Our results provide evidence that this supplementation program with 100% natural-origin broodstock provided a long-term demographic boost to the population (mean of 4.56 times in the 1st generation and mean of 2.52 times in the 2nd generation). Overall when spawning in nature, hatchery-origin fish demonstrated a trend towards lower RS compared to natural-origin fish (p<0.05). However, when hatchery-origin fish successfully spawned with natural-origin fish, they had similar RS compared to natural by natural crosses (1st generation mean hatchery by natural cross RRS = 1.11 females, 1.13 males; 2nd generation mean hatchery by natural cross RRS = 1.03 females, 1.08 males). While origin, return year, and body length were significant predictors of fitness for both males and females (p<0.05), return day was significant for males but not females (p>0.05). These results indicate that supplementation programs that reduce the potential for genetic adaptation to captivity can be effective at increasing population abundance while limiting long-term fitness effects on wild populations.