Adaptive flexibility in the behaviour of juvenile Atlantic salmon: short-term responses to food availability and threat from predation

Juvenile Atlantic salmon Salmo salar were shown experimentally to make adaptive behavioural decisions as a short-term response to changes in food availability and predation risk. Restricted food availability caused an increase in activity, whereas activity was decreased under predation threat. Although changes in activity were not more pronounced among the hunger-motivated fish, suggesting that they were not balancing risk and hunger, hungrier fish spent less time in refuges in the presence of a predator, indicating that they were more willing to take risks than satiated fish. Aggressive interactions among juvenile Atlantic salmon were decreased by predation threat, but were highest when predators were absent and food was abundant. (C) 2003 The Fisheries Society of the British Isles.