Survival benefits of antipredator training in captive-reared salmon: impact of behaviour, health, and genetics

Releasing captive-reared animals into the wild is a common population management practise, but their inexperience with predators often leads to high post-release mortality. Although captive animals can be trained to recognize and respond to predatory cues, the post-release survival benefits of this method remain uncertain. Additionally, how factors related to captive breeding and rearing-such as hybridization and disease, which can affect learning and memory-influence the effectiveness of antipredator training has not been investigated. We conducted two experiments with Atlantic salmon (Salmo salar), during which they first underwent antipredator training via paired exposure to predator cues (Northern pike, Esox lucius) and conspecific alarm cues, followed by release into semi-natural streams for predation trials with live pike. The first experiment focused on post-release behaviours and demonstrated innate predator avoidance that was not enhanced by the training. In the second experiment, genetic background (purebred versus hybrid crosses) and parasite infection status (trematode eye fluke, Diplostomum pseudospathaceum) of the salmon were manipulated to assess their effects on antipredator learning. This experiment demonstrated a clear survival benefit from the training, which was not influenced by either the genetic background or infection. The variation in effectiveness of the antipredator training between the experiments may be attributed to different experimental environments and developmental stages of the salmon. Overall, our findings suggest that antipredator training conducted under specific conditions enhances post-release survival of captive-reared salmon, providing valuable insights for reintroduction and population augmentation programmes.