Do habitat restoration efforts and the associated releases of hatchery‐reared fish affect the genetic diversity and integrity of native brown trout populations?

Habitat restoration may protect brown trout (Salmo trutta) populations from loss of genetic diversity by increasing environmental carrying capacity and, consequently, population size. However, the accompanying release of hatchery-reared fish may threaten the genetic integrity of native populations through introgression. We monitored the genetic composition of four native brown trout populations using 16 putatively neutral microsatellite loci in small boreal streams subjected to restoration measures and the release of hatchery-reared brown trout. Sampling was conducted before restoration, during the expected recovery phase, and after recovery. Analysis of population composition over the 19-year study period indicated interbreeding between hatchery and wild fish shortly after the releases, but the most recent samples predominantly represented native, presumably resident genotypes. Restoration treatments had no detectable effects on the genetic diversity of the small study populations. Our results add to the evidence suggesting that stocking with non-native fish is ineffective in enhancing wild populations.