Multifaceted environmental enrichment in industrial fish hatcheries: the influence of enriched rearing on the in-situ behaviour and post-stocking success of juvenile Atlantic salmon (Salmo salar)

Hatchery fish reared and stocked to sustain or restore wild populations often perform poorly in novel environments compared to their wild counterparts. To combat maladaptive hatchery-acquired traits environmental enrichment is an emerging tool used to provide ‘life skills training’ to hatchery fish prior to release. Through the application of simple yet multifaceted enrichment protocols in an industrial fish hatchery, this thesis aimed to demonstrate how enrichment could be applied to improve the ecological viability of stocked fish. At a provincially-run fish hatchery, a subgroup of juvenile Atlantic salmon (Salmo salar) were subject to 10 weeks of environmental enrichment (live food, live predators, in-tank structure) and their performance metrics were assessed and compared to non-enriched fish. In-situ behavioral response data revealed that enriched fish had significantly (57%) better foraging abilities throughout all behavioural trials assessed. Non-enriched fish exposed to a predatory chemical stimulus (Rainbow trout, Oncorhynchus mykiss) showed significantly better antipredator tactics supported by reductions in foraging behaviours, but not by reductions in movement behaviours. Post-stocking field data concluded that passive integrated transponder (PIT) tagged salmon (n = 2,039) stocked into Duffins Creek (Ajax, ON) had 1.6% higher in-stream detection rates and significantly faster movement speeds (13%) within the first 5rkm when compared to non-enriched fish. Additionally, acoustically tagged salmon (n = 60) demonstrated that the detection proportion of enriched and non-enriched fish was similar throughout the first 5rkm of the creek, but enriched fish had ~10% higher detection proportions and 32% faster movement speeds onward to Lake Ontario (20rkm). The information presented in this thesis demonstrates the significant benefits of environmental enrichment and has implications for fisheries management and restoration efforts