Diversity and Community Structure of Coastal Elasmobranchs in the French West Indies

Coastal elasmobranchs play key functional roles in Caribbean reef ecosystems, yet their populations have declined markedly across the region. To address major knowledge gaps in the French West Indies (FWI), we characterised recorded coastal elasmobranch assemblages in Guadeloupe, Martinique, Saint-Barthélemy and Saint-Martin using two independent observational datasets analysed separately: 1243 baited remote underwater video system (BRUVS) deployments conducted between 2016 and 2024 and 14,998 dives reported through the INA SCUBA citizen-science programme between 2019 and 2024. Sampling completeness, alpha and beta diversity, dominance patterns and species-specific encounter rates were assessed within each dataset. Across both datasets, 11 taxa were recorded: ten by BRUVS and five by INA SCUBA, with four shared between methods. In both datasets, Saint-Barthélemy had the highest mean richness and diversity with frequent detections of reef-associated sharks, whereas Saint-Martin showed an intermediate pattern. Guadeloupe and Martinique had lower sample-level richness and recorded assemblages dominated by a limited number of taxa, particularly the southern stingray, while reef-associated sharks were rare or not detected. BRUVS and INA SCUBA provided distinct but partly overlapping observational coverage; however, unequal sampling effort, site selection, temporal coverage, and species-specific detectability limit inter-island inference. These results provide a regional baseline for continued monitoring and for testing the ecological and anthropogenic factors that may underlie the observed spatial patterns.