Common-garden comparison of relative survival and fitness-related traits of wild, farm, and hybrid Atlantic salmon Salmo salar parr in nature

: When escapee farmed Atlantic salmon Salmo salar interbreed with wild fish, the introgression of maladaptive genes can lower wild population productivity and alter key life his-tory traits. To date, only a few European studies have compared wild, farm, and hybrid salmon under common conditions in the wild, isolating the influence of genetics on survival and fitness-related traits. Here, we examined the performance of experimentally derived Atlantic salmon fry from 4 cross types (wild, farm, and reciprocal F 1 hybrids) during the first summer of growth at 3 locations in southern Newfoundland. Overall survival was high, with the cross type rank order consistent across sites (mean percent recaptured: wild-mother hybrids 26.2% ≈ wild 26.0% > farm 19.2% > farm-mother hybrids 12.8%). Wild fish were smaller than wild-mother hybrids and farm fish, though differed less in size from farm-mother hybrids. At 2 out of 3 sites, wild-mother hybrids were larger than wild and farm-mother hybrid fish but had only a small size advantage over farm fish. Shape differences were small and mainly related to body depth, with the largest differences between wild and farm fish. Wild-mother hybrids had fewer parr marks than other cross types at a single site, and though differences in the size of marks were minimal, farm fish tended to have the narrowest marks. Overall, these results show that genetic differences exist for fitness-related traits among wild, farm, and hybrid juveniles, even over short temporal scales and under favourable environmental conditions, and may contribute to patterns of reduced farm-mother hybrid and feral farm survival in the wild.