Sharks, as apex predators, play a fundamental role in most coral reef ecosystems by influencing communities directly via predation or via behaviourally mediated trophic interactions (Heithaus et al. 2008). Healthy coral reefs are generally regulated by small sharks, such as grey reef sharks (Carcharhinus amblyrhynchos). Although small sharks have been found in the stomachs of the great hammerhead shark (Sphyrna mokarran) (Cliff 1995), direct observations of predation on free-living reef sharks are absent. Here, we report upon a great hammerhead shark preying on a grey reef shark at the World Heritage atoll of Fakarava (French Polynesia).
Schools of grey reef sharks have often been observed to be frightened by great hammerhead sharks and to pursue their assailant. Several hypotheses may explain the response of the other grey reef sharks: a collective mobbing as found in dolphins or seals (Kirwood and Dickie 2005) or simply an attempt to feed opportunistically on the carcass. Although sharks may not be a major component of the great hammerhead shark’s diet, this rare field observation confirms previous data from stomach contents, further documents this predator–prey interaction and highlights the complexity of the trophic food chain in healthy coral reef ecosystems.
We are grateful to TOPDIVE, especially to Sébastien Jolivet, for their contribution to the description of the event. We are grateful to Ludovic Jego and Christian Hornecker for providing the photographs.