Variance in Reproductive Success is Driven by Environmental Factors, not Mating System, in Bonytails

Studying the reproductive ecology of aggregate broadcast‐spawning fishes is difficult because it is generally not feasible to sample all potential parents and unambiguously assign their offspring. We used molecular‐based parentage analysis to gain insights into the reproductive ecology of the endangered Bonytail Gila elegans and to evaluate whether protected off‐channel habitats could be used as an alternative to hatchery production. By genotyping adults and offspring ( n  = 4,130) that were stocked into two experimental backwaters across 3 years, we determined that most adults (82–97%) contributed to progeny production across years and backwaters, with one exception. Both sexes exhibited multiple matings, and the number of mates and family size were positively correlated. There was also a positive correlation between adult size and metrics of reproductive success. There were strong interactions between sample year and backwater, suggesting that environmental factors are the primary driver of variance in reproductive success. Knowledge of mating systems and sources of variance in reproductive success is important for management of endangered fish because high variance in reproductive success leads to substantial losses of genetic variation when few individuals reproduce successfully. Although variance in reproductive success was observed, most adults contributed to genetically diverse progeny in experimental backwaters. These results support the use of predator‐free—but otherwise natural—backwaters as an effective conservation tool for reintroducing the Bonytail to its native habitat.