Following preliminary underwater observations of about 1000 h carried out monthly between 2012 and 2023 (except the years 2021 and 2022), 23 specimens of grey reef sharks were spotted and photo-identified off the coast of Nosy Be in Madagascar, on an emerging reef called “Mokarran” at a depth between 15 and 30 m. Over 10 years of observations, eight specimens were re-sighted, identified with a non-invasive photo-identification technique of part of the first dorsal and the caudal fin, and one specimen was re-identified after 1982 days from the first sighting, i.e., after more than 5 years. In addition, six specimens of probably pregnant females were also identified in the same area. The population was entirely made up of females. The aggregation area could represent a new nursery site which, if confirmed after further investigations, will require greater protection.

The spinner shark is a widely distributed coastal species that faces significant anthropogenic pressures, yet information on its ecology in the western Indian Ocean remains poorly documented. This study provides preliminary baseline observations on temporal occurrence, sex ratio, and size distribution of a bait-attracted spinner shark aggregation in Hulhumale (North Malé Atoll, Maldives) and presents the first individual-level photo-identification (photo-ID) catalogue for the species based on underwater observations. Surveys were conducted in November 2024 and November 2025 using underwater photography, video recordings, and laser photogrammetry. In total, 69 individual spinner sharks were identified using the standard photo-ID protocol which proved to be valid. On the contrary, the preliminary application of the semi-automatic Identifin software indicated possible effectiveness for individual recognition; however, its performance cannot be reliably validated in this area because of poor image quality and environmental turbidity. Six individuals were re-sighted across years, demonstrating the feasibility of non-invasive repeated, long-term monitoring through photo-ID. Although interannual variation in sex ratio of sharks observed was detected (χ² = 10.56, p = 0.0012), this pattern should be interpreted cautiously due to provisioning-related sampling bias and unequal sampling effort across years. Total length measurements (n = 28) indicated predominantly adult and subadult individuals, with no apparent interannual differences in size distributions. Overall, this study establishes a methodological baseline for spinner shark photo-ID in the Maldives and highlights the importance of multi-year and multi-season monitoring to robustly evaluate aggregation dynamics, site fidelity, and population-level patterns in this region.