| Summary: | The impact of Atlantic salmon S. salar farm escapes/intentional releases of non-native salmon and stocking of fertile farm/hatchery reared individuals on the genetic integrity, fitness and long-term viability of wild populations has been the focus of considerable debate. In this study, the consequences of both a S. salar supplemental stocking programme and the long-term consequences of farm escapes are assessed. AS. salar supplemental stocking programme was established in 1996 in the River Bush, Northern Ireland, in an effort to increase the diminishing adult returns. Capitalising on this programme, in this study, 40 wild males and 40 wild females were selected as broodstock. Eggs were stripped from females and fertilized in vitro to produce 40 unique families. Resulting eggs were reared under hatchery conditions. ~90,500 un-fed fry were stocked into areas with limited spawning potential. >2,400 smolts were intercepted and genotyped for a suite of microsatellite markers and assigned to the parental broodstock. Analysis revealed that the overall percentage survival of the stocked hatchery-reared fish was 0.66%. Results are considered in terms of costs (e.g. potential genetic consequences related to mate choice) & benefits (e.g. increased production). In two classic studies, Clifford et al. (1998a, 1998b) investigated large S. salar escapes, involving adult and juvenile individuals, and their impacts on wild populations. Based on their findings the authors demonstrated that only a small proportion of adult escapes managed to successfully breed in the wild. They have also suggested that escaped juvenile farm salmon can potentially complete their life cycle, breed and interbreed with native fish upon their return to the river. In the current study, the sites of Clifford's studies were revisited 20 years later. New samples were collected and screened alongside the samples used in Clifford's studies, as well as additional samples not screened at the time. In total over 3,000 S. salar were screened for 25 microsatellites and one mitochondrial DNA marker, known to be associated with farmed fish. Results of analyses confirm limited impact of adult salmon escapes on wild populations and provide good evidence for the establishment of a farm derived population in the wild.
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