Species diversity, abundance, biomass, size and trophic structure of fish on coral reefs in relation to shark abundance

Theory predicts that loss of gape-limited sharks should lead to increases in the abundance and biomass of smaller size classes of prey. We used stereo-baited remote underwater video stations (stereo-BRUVS) and stereo diver-operated video systems (stereo-DOVS) to characterise the shark and fish assemblages on 2 remote, atoll-like reef systems in northwestern Australia, the Rowley Shoals and the Scott Reefs. Whereas the Rowley Shoals is a marine protected area, sharks have been removed from the Scott Reefs for over 3 centuries. We found that sharks were significantly more diverse, more abundant, larger in size and greater in biomass in the marine reserve relative to the Scott Reefs. Consistent with a priori hypotheses, bony fishes displayed greater species diversity, abundance and biomass where sharks were common relative to the predator-depleted location. The size and trophic structure of bony fish assemblages also differed between locations. Our results provide large-scale evidence consistent with the hypothesis that reef-associated sharks are gape-limited trophic omnivores that impose top-down effects on medium sized (