Populations of sharks and other marine predators have declined dramatically worldwide. Because sharks play a role in the dynamics of their ecosystems and there is increasing interest in rebuilding populations, understanding the factors influencing their abundances and assemblage structure are important for proper conservation management. French Polynesia is the world’s largest shark sanctuary and features gradients of environmental and anthropogenic factors; it therefore provides a model system for elucidating the factors that affect the abundance and assemblage compositions of elasmobranchs and large teleost predators. Using ~3000 hours of baited remote underwater video data collected across 17 islands and 35 reefs, I found that the relative abundances of sharks at high islands were only one third of that on atolls, and open atolls had abundances nearly 20% higher than closed atolls. Therefore, realistic conservation targets for reef sharks in the Indo-Pacific should account for island geomorphology. Other environmental factors had smaller effects and human pressures (market gravity) did not significantly influence abundances. Assemblages at most islands generally lacked rays and were dominated by blacktip reef sharks (Carcharninus melanopterus) and grey reef sharks (Carcharhinus amblyrhynchos). There was, however, significant variation in elasmobranch assemblages across French Polynesia. Species assemblages and associations, particularly at smaller scales, may be shaped by species interactions. Relative abundances of predatory teleosts from the families Lutjanidae, Scombridae, Megalopidae, Carangidae, Sphyraenidae, Serranidae, and Lethrinidae on 19 reefs across 11 different islands/atolls varied positively with net primary productivity. Island geomorphology, human population density, relative abundance of sharks, and sea surface temperature, also influenced predatory teleost abundances. Interestingly, higher abundances of teleosts were found on reefs with higher abundances of sharks. However, unlike sharks, predatory teleosts appear to be sensitive to fishing pressure at even low human population densities. Higher abundances of predatory teleosts and sharks, together, are generally positively associated with healthier reefs as measured by percent cover of hard corals and crustose coralline algae. The relationships between coral health, small teleosts, and both groups of predators, however, were non-linear and it is unclear if the presence of predators helps facilitate reef health or if healthier reefs attract greater abundances of predators.
