AEI prepress abstract   -  DOI: https://doi.org/10.3354/aei00441

ABSTRACT: Selection due to multi-generational domestication and genetically distinct origins raise concerns about potential fitness consequences of hybridization between farmed and wild Atlantic salmon. In Newfoundland (NF), Canada, the aquaculture industry uses the North American (NA) Saint John River strain, though site-specific permission has been granted to farm a European origin (EO) strain. We used complementary experiments to investigate differences in (1) dominance status and (2) growth and survival in allopatry (NF wild fish) versus sympatry (NF wild fish with NA/EO farmed individuals and related F₁ hybrids) in contrasting tank and semi-natural stream environments. NA farmed salmon were more dominant than NF wild individuals, with hybrids being intermediate and not differing from wild. EO farmed salmon also tended to dominate NF wild individuals, but not significantly. Competition with farmed fish and hybrids did not affect the growth of wild fish in sympatry versus allopatry in the tank environment. However, that was not the case in one instance in the stream environment where wild fish in sympatry with NA farmed fish and hybrids outgrew those in allopatry. Within sympatric treatments, both EO and NA farmed salmon outgrew wild individuals in the tank environment, but not always in the stream environment (exception NA farmed). Hybrids tended to display intermediate growth performance relative to farmed and wild fish in both environments. Survival did not differ among cross types in either environment. These findings suggest that, irrespective of distinct origins, both EO and NA farmed salmon displayed greater dominance and growth than NF wild salmon in the tank environment. However in the stream environment, competition imposed by NA farmed fish and related hybrids on wild fish appeared less than that imposed by the EO strain and related hybrds, as evident in growth performance.