Using Citizen Science to Infer Characteristics and Habitat Use of Reef Manta Rays (Mobula Alfredi) in New Caledonia

Abstract

Abstract Reef manta rays (Mobula alfredi) are observed at several sites in all parts of the archipelago of New Caledonia. The species faces threats from human exploitation and activity in several regions of the world and crucial information on the ecology of the species is needed. This study is the first to investigate the population of New Caledonia and focuses on its characteristics and its habitat use. We used citizen science over four years (2015–2020) to collect 1741 photo-identifications from 11 sites. The unique ventral coloration patterns of the manta rays allowed the identification of 391 individuals. These results highlight the widespread distribution of the species in the archipelago with little connectivity between all aggregations sites, with only 5.4% of the individuals observed at more than one site. Strong and long-term site fidelity was recorded at all studied sites through re-sighting rates and residency analysis. The population also records the highest known proportion of melanistic manta rays (43%) to date, and a balanced male : female ratio (1.0 : 1.15). The analysis of injuries reported a low impact from anthropogenic stressors, with only 9.8% of injuries judged to be of anthropogenic origin. Attempted predation rates were not higher than other location in the world with 29.7% of individuals bearing bite-related injuries. Our study highlights the need for further investigations on the spatial ecology and structure of the population to assess essential habitat and address potential localised threats, and thus, inform by conservation projects.