Consequences of Environmental Manipulation on Behavioural and Neuromorphological Plasticity as It Relates to the Reintroduction of Atlantic Salmon (Salmo salar) to Lake Ontario

The reintroduction of imperilled species has become an important tool in conservation biology and relies on the captive-rearing of remaining individuals, or a subset thereof, as a lifeline to prevent extinction. The success of reintroduction efforts has generally been low, mainly due to poor post-release performance of captive-reared animals. Captive-breeding programs tend to produce behaviourally and neurologically compromised animals that deviate from wild phenotypes and are less fit in natural settings. While genetic adaptation can account for some of the behavioural deficiencies expressed by captive-reared animals, phenotypic plasticity has been shown to play a large role. Phenotypic plasticity is generally defined as the ability of an individual to produce different phenotypes, or change the trajectory of phenotypic development, when exposed to different environmental conditions. This thesis proposes that by understanding the environmental factors and mechanisms that shape the phenotype, conservation biologists and managers alike can alter the rearing conditions and release protocols of captive-bred animals destined for stocking to increase the success of reintroduction efforts. Throughout this thesis I examine the effects conditioning tactics – methods aimed at manipulating the rearing environment and release protocol to counteract the negative effects of captive-rearing on fitness-related behaviours in Atlantic Salmon (Salmo salar). Specifically, I investigated the effects of manipulating the early developmental rearing via enrichment (sensory enrichment via alarm cue exposure and physical enrichment via increased structure in the rearing environment) on anti-predator related behaviours. Alarm cue exposure during early development had no significant effect on anti-predator related behaviour but fish exposed to alarm cue showed significant plastic changes to regional brain volumes (smaller olfactory bulbs), suggesting the potential for alarm cue to affect post-release behaviour. Physical enrichment during early development resulted in more wild-like behavioural phenotypes but did not ameliorate behavioural effects associated with stressful transport. I also investigated the effect of soft-release tactic – providing an in-stream acclimatization period prior to release– on the movement behaviour of fish released to the wild. Soft-released fish significantly differed from conventionally released (hard-release) fish in movement patterns, more closely matching wild-like movement pattern for this species. Finally, I investigated the effects of embryonic exposure to an artificial odorant (morpholine) and tested for behavioural evidence of imprinting at later developmental stages using two separate analytical approaches. Fish exposed to morpholine during the embryonic stage showed evidence for imprinting (a phenotypic plastic response) at the smolt stage but not the parr stage. This suggests that imprinting can be detected at a stage relevant for reintroduction efforts and provided support for the use of time-sensitive analyses when testing for behavioural evidence of imprinting. This thesis provides supports for the use of conditioning tactics to manipulate phenotypically plastic responses to aid in the successful establishment of reintroduced animals to the wild. It also provides insight into the mechanisms involved in phenotypically plastic responses to changing environments.

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