Fig. 3: Time taken by teleost mesopredators to begin feeding on fish baits is greater on vertical than horizontal axes and in the presence of a shark model than controls.

The use of models to invoke anti-predator behaviour has a long history in ecology, particularly in studies of avian communities. Recent work has expanded this approach into coral reef environments using models of reef sharks and smaller teleost predators to examine the response of herbivorous and mesopredatory species to different scenarios of predatory threat. Lester et al.¹⁶ examined the willingness of mesopredatory lutjanid, serranid and lethrinid fishes to venture onto the sand beside and into the water column above coral patches to feed on fish baits. Baits were deployed at three distances along a horizontal axis on the seabed perpendicular to the reef and in a vertical axis in the water column above the reef. Horizontal and vertical deployments occurred separately. Predator threat was manipulated by the presence of life-size models of a common reef shark, the reef blacktip (Carcharhinus melanopterus, a predator and/or lethal competitor) and a model of a small, non-threatening mesopredator (a coral trout, Plectropomus sp., a competitor) and object controls (silhouettes). Crosses and lines show mean time taken to first bite on the baits on a horizontal axis (blue) and a vertical axis (tan) at different distances from the reef (A). As the distance from the patch reef increased, it took longer for mesopredators to initiate feeding and the amount of time increased when the model reef shark was deployed. Importantly, the average time taken for feeding to commence above the patch reef in the presence of the shark model was almost twice the amount taken over the sand at just under half the equivalent distance from the reef. This showed that these smaller mesopredators were far more sensitive to the threat of predation away from shelter in vertical than horizontal axes—effectively defining an elongated hemisphere of risk around the patch reefs (B). Lester et al.¹⁶ argued that on the sand, mesopredators were protected from attack from below whereas above the reef, these fishes were particularly vulnerable, given the placement and sensitivity of their sensory systems (notably vision). Data sets re-plotted from Lester et al.¹⁶. Image artwork credit: Dean Tysdale.