One challenge in studying the natural behaviour of wild animals is the requirement of detailed observations spanning extended periods of time, which is particularly difficult in the case of sharks. As a result, remote sensing technologies are increasingly employed in which the data received is considerably simplified. In this study, 475 blacktip reef sharks (Carcharhinus melanopterus) were identified using direct underwater observation. Subsequent sightings of these sharks were recorded at various locations along the north shore of Mo'orea Island over a period of 6.5 years. The key factors influencing their movements were found to be the reproductive season and the lunar phase. Additionally, a tendency to avoid turbulent regions was observed, particularly by mature females. Notably, significant variations existed among individuals; while some sharks left their ranges for only two weeks twice a year for mating and parturition, others were frequently absent, sometimes for months at a time. It was also observed that juveniles displayed high mobility prior to settling into a home range around the ages of three to four. Understanding such movements will be useful in the future in the planning of MPAs and other conservation strategies.

The chondrichthyan lineage diverged from the osteichthyan line around 440 million years ago, resulting in a vast evolutionary gulf between modern elasmobranchs and other vertebrates. Though this has supported the assumption that sharks are ancient, dangerous, and binary-minded, intelligent actions including social interactions have been noted in the field, while laboratory studies have confirmed a variety of cognitive capacities. Yet, due to fear of sharks and the difficulties of observing them in their aquatic environments, few ethological studies have been done, so their natural behaviour remains little known. On noting that Carcharhinus melanopterus displayed complex actions during incidental meetings, a long-term ethological study of the species was carried out on the north shore of Mo’orea Island, French Polynesia. During the 6.5 years of the study, new behaviours continued to present. The 35 context-specific actions identified as comprising the behavioural repertoire of C. melanopterus are described.