Dominance relationships and behavioural correlates of individual spawning success in farmed and wild male Atlantic salmon, Salmo salar

1. Variance in competitive ability among males should lead to a corresponding skew in reproductive success. Atlantic salmon (Salmo salar) males form dominance hierarchies during spawning, such that the dominant individuals are predicted to realize the highest reproductive success. However, the degree to which this occurs depends on various genetic and environmental factors. 2. We investigated the influence of the aquaculture environment on male Atlantic salmon behaviour during spawning in three experiments involving groups of either purely farmed or wild males, or mixed groups composed of equal numbers of farmed and wild fish. The objective of this study was to compare and contrast the formation of dominance hierarchies and relationships between aggression, courtship and spawning success in farmed and wild males. 3. Although farmed males did not establish dominance hierarchies as effectively as wild males, they courted and spawned with females in larger numbers and they frequently failed to release sperm when females released eggs. 4. Dominance structures established by wild males led to reliable behavioural correlates of spawning success; this was not the case among farmed males. 5. From the risk-assessment perspective, farmed males can be expected to have reduced spawning success, although the degree of reproductive inferiority of farmed relative to wild males depends upon rearing environment and the populations under consideration.