Hatchery supplementation programs are designed to enhance natural production and maintain the fitness of the target population; however, it can be difficult to evaluate the success of these programs. Key to the success of such programs is a relatively high reproductive success of hatchery fish. This study investigated the relative reproductive success (RRS) of steelhead Oncorhynchus mykiss (anadromous rainbow trout) by creating pedigrees for hatchery and natural spawning steelhead. We genotyped adult steelhead that returned to a weir and were released upstream to spawn in Little Sheep Creek, a tributary to the Imnaha River in eastern Oregon. The broodstock for this supplementation program were originally chosen from natural‐origin steelhead returning to the weir and in subsequent years consisted of both natural‐ and hatchery‐origin individuals. Microsatellite analyses showed the broodstock to be genetically similar to the natural population across years. We also genotyped adult resident rainbow trout from multiple locations upstream of the weir and determined the parentage of progeny collected at various life history stages, including returning adults in subsequent years. Analysis of progeny sampled at both the juvenile and adult life stages suggested that the RRS of hatchery‐origin fish was 30–60% that of their natural‐origin counterparts. Using generalized linear models to address the importance of various factors associated with reduced reproductive success, we found that the greatest effects on RRS were origin (natural versus hatchery), length, return date, and the number of same‐sex competitors. Natural parents were less negatively affected by same‐sex competitors. Differential survival of juveniles and the behavior of offspring and/or spawning adults may all contribute to diminished fitness in hatchery‐reared salmon, although it could not be determined to what extent these effects were of a persistent, heritable nature as distinct from an environmental effect associated with hatchery rearing and release strategies.

Studies have demonstrated higher postrelease survival for larger hatchery steelhead Oncorhynchus mykiss smolts than for smaller ones. However, the ideal release size should also maximize adult returns and minimize interactions of hatchery fish with wild fish. We conducted a study over five release years with paired groups of anadromous hatchery steelhead smolts reared to target sizes of either 90 g (small size) or 113 g (large size). After stream release, we monitored out‐migration travel times and survival to a downstream dam using freeze‐brand marks in a subsample of each release group. Steelhead smolts that out‐migrate quickly may interact less with wild fish. Across all release groups, travel time was about 3 d slower for small‐sized smolts than for large ones, but this difference was not statistically significant, and there was no significant difference in the percentage of brands detected at the dam between the two smolt sizes. Coded wire tag recovery was used to compare smolt‐to‐adult survival (SAS), the number of adults produced per 100 kg of smolts released, and the percentage of adults that strayed. Across all years, large‐sized smolts had an average SAS of 1.31% compared with 0.92% for small‐sized smolts, a statistically significant difference of 42.0%. The average number of adult steelhead produced per 100 kg of smolts released also was higher for the large‐sized group (11.4 adults/100 kg of smolts) over the small‐sized group (10.1 adults/100 kg of smolts), though the 12.8% difference was not statistically significant. Adults originating from large‐sized smolt releases strayed at a rate of 13.1% compared with a 7.9% rate for the small‐sized smolt groups, a difference that was statistically significant. In this study, larger hatchery steelhead smolts had a higher survival after release; however, we found tradeoffs between management objectives associated with maximizing adult production and those aimed at minimizing ecological risks.

In a study using 14 paired‐release groups over 10 release years, we compared the performance of hatchery summer steelhead Oncorhynchus mykiss that were acclimated as smolts (AC) for 16–57 d before release into ponds supplied with ambient stream water with that of fish trucked from the hatchery and directly released (DR) into Spring, Deer, and Little Sheep creeks in northeastern Oregon. After releasing the fish into streams, we monitored out‐migration travel times and survival to Lower Granite Dam (LGD) on the Snake River using freeze brand marks or implanted passive integrated transponder tags in a subsample of each release group. Across all release groups, travel time was significantly slower for AC fish (34.7 d) than for DR fish (31.8 d), though there was no significant difference in survival probability to LGD. We used recoveries of coded wire tags to estimate smolt‐to‐adult survival (SAS) and a stray rate index (SRI) for the AC and DR strategies. Across all release groups, SAS was 33% higher and SRI 42% lower for AC steelhead. At each release site acclimation increased average SAS by at least 11% and decreased SRI by at least 16.5%. We found a significant, negative linear relationship between travel time to LGD and SAS; however, there was no significant relationship between survival to LGD and SAS, which implies that judgments about the success or failure of a novel rearing or release strategy should not be made based on out‐migration survival. Acclimating juvenile steelhead produced significantly higher SAS and lower SRI in the hatchery program we evaluated; however, our results are not consistent with those of other steelhead acclimation studies.