Combining Genetics and Demographics in a Viability Model of Hatchery-Wild Systems Subject to Environmental Change

Hatchery-reared and naturally-produced (“wild”) salmonids experience different selective pressures. Rates of interbreeding between these two groups constrain adaptation to the natural environment. The processes affecting hatchery-wild dynamics have been studied by researchers interested in niche evolution of source-sink systems. I used an individual-based model originating from the theory of niche evolution to explore the effects of different proportions of hatchery fish spawning in the wild and wild fish spawned in hatcheries on long-term adaptation and persistence. The model uses a multi-locus quantitative trait to determine demographic performance of individuals, and relaxes assumptions made in previous continuous-state analytical models. I simulate change in the optimal phenotype of individuals spawning in the wild (i.e., environmental change) and record the persistence of wild-born individuals under different rates of interbreeding with hatchery fish, both in the hatchery and in the wild. Different probabilities of persistence were obtained from the same level of a Proportionate Natural Influence (PNI), suggesting that PNI alone does not predict persistence under certain conditions. Results are sensitive to rules about “mining” wild fish broodstock at low abundances, further suggesting a need to optimize the take of broodstock through time as a function of wild spawner abundance.