Data from: Effective size of a wild salmonid population is greatly reduced by hatchery supplementation

Many declining and commercially important populations are supplemented with captive-born individuals that are intentionally released into the wild. These supplementation programs often create large numbers of offspring from relatively few breeding adults, which can have substantial population-level effects. We examined the genetic effects of supplementation on a wild population of steelhead trout (Oncorhynchus mykiss) from the Hood River, Oregon, by matching 12 run-years of hatchery steelhead back to their broodstock parents. We show that the effective number of breeders producing the hatchery fish (broodstock parents; Nb) was quite small (harmonic mean Nb=25 fish per brood-year vs. 373 for wild fish), and was exacerbated by a high variance in broodstock reproductive success among individuals within years. The low Nb caused hatchery fish to have decreased allelic richness, increased average relatedness, more loci in linkage disequilibrium, and substantial leve ls of genetic drift in comparison to their wild-born counterparts. We also documented a substantial Ryman-Laikre effect whereby the additional hatchery fish doubled the total number of adult fish on the spawning grounds each year, but cut the effective population size of the total population (wild and hatchery fish combined) by two thirds. We demonstrate that, in this system, the Ryman-Laikre effect is most severe when (1) more than 10% of fish allowed onto spawning grounds are from hatcheries and (2) hatchery fish have high reproductive success in the wild. These results emphasize the tradeoffs that arise when supplementation programs attempt to balance disparate goals (increasing production while maintaining genetic diversity and fitness).许多种群数量下降且具有重要商业价值的野生种群，会通过人为释放人工繁育个体的方式获得种群补充。这类种群补充项目通常仅依靠少量繁育亲体即可产生大量子代，进而对种群整体造成显著影响。本研究以美国俄勒冈州胡德河的野生硬头鳟（steelhead trout，*Oncorhynchus mykiss*）种群为对象，通过将12个洄游季的孵化场繁育硬头鳟回溯至其繁育亲体，分析了种群补充行为对该野生种群的遗传效应。 研究结果显示，繁育孵化场子代的亲体有效种群数量（繁育亲体；Nb）极低——每繁育季的调和平均Nb为25尾，而野生种群的Nb则为373尾，且年内个体间繁育亲体繁殖成功率的高变异进一步加剧了这一问题。较低的Nb导致孵化场繁育个体相较于野生个体，出现了等位基因丰富度降低、平均亲缘关系升高、更多位点处于连锁不平衡状态，以及显著的遗传漂变现象。 本研究还记录到了显著的莱曼-莱克尔效应（Ryman-Laikre effect）：每年补充的孵化场个体使产卵场的成鱼总数翻倍，但却使种群整体（野生个体与孵化场个体的总和）的有效种群规模缩减了三分之二。本研究表明，在该研究系统中，莱曼-莱克尔效应在以下两种情况下最为显著：一是允许进入产卵场的孵化场个体占比超过10%；二是孵化场个体在野外具备较高的繁殖成功率。 上述研究结果凸显了种群补充项目在平衡多重目标——即提升种群产量的同时维持遗传多样性与适合度——时所面临的权衡取舍。