Differences in antipredator behaviour between wild and hatchery-reared juvenile Atlantic salmon (Salmo salar) under seminatural conditions

Captive rearing may elicit experiential or genetically based changes to salmonid antipredator behaviour, which may reduce survival of hatchery-reared fishes when they are released into the wild. Nevertheless, few studies have compared the behaviour between local wild-caught and local hatchery-reared fish (two generations or less), and none have clone so under natural conditions. We conducted a seminatural field study comparing the antipredator behaviour of wild-caught, F1 (offspring of wild-caught adults) with that of F2 (second generation) hatchery-reared young-of-the-year Atlantic salmon (Salmo salar, from the same source population) in response to standardized chemical alarm cues. Wild-caught salmon exhibited the strongest antipredator response to a standardized threat (conspecific alarm cues), while F2 salmon exhibited the weakest response. F1 salmon were intermediate in their behavioural response. The observed differences between wild-caught and F1 salmon suggests that differential experience may play a significant role in predator avoidance behaviours. Furthermore, the observed differences between F1 and F2 salmon suggests that even one full generation of hatchery rearing may be sufficient to select for maladaptive responses to predators under natural conditions. Given the controversy regarding the effectiveness of hatchery programs for conservation use, the results of this study suggest that minimizing hatchery time may reduce the behavioural differences between wild and hatchery-reared fishes.