Interspecific competition among juvenile salmonids: social behaviour and HORMONE LEVELS OF ATLANTIC SALMON AND TWO NON-NATIVE TROUT SPECIES

Competition with ecologically similar non-native salmonids may hinder efforts to restore Atlantic salmon (Salmo salar) in Lake Ontario. I examined the competitive effects of juvenile brown trout (S. truttci) and rainbow trout (Oncorhynchus mykiss), two non-native competitors, on aggression, dominance, growth, and hormone concentrations of three candidate strains of juvenile Atlantic salmon selected for réintroduction into Lake Ontario. Interspecific competition in semi-natural streams reduced aggression, dominance, and growth of Atlantic salmon, coincident with increasing concentrations of cortisol, a hormone that functions in part in the stress response. An aggression-associated hormone, 11-ketotestosterone, was largely unaffected. Interestingly, the most ecologically similar competitor, rainbow trout, had less impact on Atlantic salmon behaviour and growth, relative to brown trout. Atlantic salmon from Lac Saint-Jean were least affected, implicating genetic differences among strains and specific management recommendations. This study highlights the necessity of competition experiments to understand how competition may influence restoration of extirpated populations