Out of sight, out of mind: Removal of predators by fisheries alters reef fish behaviour.

Pervasive human activities have led to the extirpation of predator species in many ecosystems. Understanding the extent and mechanisms by which such predator loss influences prey behaviour is critical for predicting the ecological consequences of trophic downgrading. We investigated reef fish behaviour in response to predator presence within and outside a protected area in the South Andaman Islands, India. We used 3D printed models to simulate the presence of two different types of predators; a sit-and-wait predator, a grouper (Mycteroperca rosacea) and a wide-ranging pursuit predator, a barracuda (Sphyraena barracuda). We recorded foraging, vigilance, and movement behaviours of herbivorous and invertivorous fish encountered in each plot. Overall, we found that fish were significantly more vigilant in response to both predator models compared to a non-predator control within protected areas but not outside protected areas. Foraging behaviour was suppressed by the predator treatments; however, herbivorous and invertivorous fish responded differently within protected areas. Fish movement behaviours also differed across predator treatments, prey foraging guilds, and areas. Anti-predator responses are thus highly contingent on habitat and both predator and prey traits. We highlight how the selective removal of predators by humans alters predation risk for prey and hence their risk-sensitive behaviours.