Sexual Segregation of Blacktip Reef Sharks (Carcharhinus melanopterus) at Mitita Island, South Morotai, North Maluku, Indonesia

Abstract

Sexual segregation may influence habitat use, social interactions, and population organisation in reef-associated sharks. However, habitat-based and social segregation in blacktip reef sharks (Carcharhinus melanopterus) at Mitita Island remains insufficiently understood. This study investigated habitat-based and social patterns of sexual segregation in blacktip reef sharks (Carcharhinus melanopterus) at Mitita Island, South Morotai, North Maluku. Field observations were conducted at Mitita Point and Niomi Point over eight sampling days from June to August 2024, comprising 24 dives. Individual sharks were recognised through photo-identification using natural markings on the dorsal and caudal fins. Environmental conditions, benthic cover, reef fish abundance, shark occurrence, and agonistic interactions were recorded. Eighteen individuals were identified, including 12 females and 6 males. Females occurred more frequently at Mitita Point, which had greater live coral cover, higher reef fish abundance, and calmer current conditions, whereas males were observed more frequently at Niomi Point. Exploratory Poisson regression indicated that current velocity score and salinity were associated with female occurrence; none of the measured environmental variables significantly predicted male occurrence. Analysis of “Give Way” interactions suggested that females occupied more central positions within the observed interaction network. The findings indicate sex-related differences in spatial occurrence and social interactions within the local aggregation. However, these patterns should be interpreted cautiously because the study involved a small identified population, two sampling stations, a short observation period, an observational design, and controlled feeding during diver-based surveys. Longer-term, seasonal, non-provisioned monitoring and movement-tracking approaches are required to determine whether the observed patterns persist across time and habitats.