Behavioural responses to conspecific disturbance chemicals enhance survival of juvenile brook charr, Salvelinus fontinalis, during encounters with predators

Several species of aquatic organisms release chemical cues upon detecting predators. These chemicals may serve to 'warn' nearby conspecifics of the predator and hence have been termed disturbance cues. Disturbance cues are thought to be low-level indicators of risk to which prey animals respond with antipredator behaviour. However, little is known about the distribution of disturbance cues among different taxa or how prey animals use these cues to mediate their risk of predation. In this study we exposed brook charr (Salvelinus fontinalis) to water from a tank containing cues of disturbed or undisturbed conspecifics at the same time as we exposed them to cues of an unknown predator, northern pike (Esox lucius). In subsequent trials, we staged encounters between the charr and a pike and tested for differences in survival. We found that charr that were exposed to simultaneous cues from disturbed conspecitics and pike odour subsequently avoided the pike significantly more than chaff that had been previously exposed to chemical stimuli from undisturbed charr plus pike odour. Moreover, pike took significantly longer to capture charr that had been previously exposed to disturbance cues from conspecifics plus pike stimuli compared to charr previously exposed to cues from undisturbed charr plus pike stimuli. Ours is the first study to demonstrate that detection of disturbance cues can provide a survival benefit during an encounter with a predator.