Characteristics, residency and site fidelity of photo-identified reef manta rays (Mobula alfredi) population in New Caledonia

June 2024

Hugo Lassauce, Olivier Chateau & Laurent Wantiez

Keywords: Spatial Connectivity • Citizen Science • Population Size • Injuries • Melanism

Summary: Reef manta rays face global threats, but minimal anthropogenic influence in New Caledonia offers a conservation reference. This study, the first on New Caledonia's manta population, used photos from 2017-2020 to identify 391 individuals. Findings show strong site fidelity, low connectivity, and a high proportion of melanistic mantas (43%). Injury analysis revealed 44.8% had wounds, with few from human activity, emphasising the area's favourable conservation context.

Abstract

“Reef manta rays (Mobula alfredi) face threats from human exploitation and activity in several regions of the world and crucial information on the ecology of the species is needed. The species is observed at several sites in all parts of the archipelago of New Caledonia where anthropogenic influence is presumed to be minimal. This study is the first to investigate the population of New Caledonia and focuses on its characteristics and its habitat use. Photographs of reef manta rays were collected directly from the authors (14.4%) between 2017 and 2020 and gathered from recreational divers and snorkelers (85.6%) from 11 sites around New Caledonia. The authors used the unique ventral coloration patterns of the manta rays that were clearly identifiable from 1741 of these photographs to identify 391 individuals and record their physical characteristics (sex, injuries, and colour morph) and resighting rates. These results highlight the widespread distribution of the species in the archipelago (11 sites) 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 (52.2% overall) and residency analysis. The population also records the world 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 that 44.8% of all reef manta rays identified (n = 391) had noticeable wounds or injuries with no significant difference in the proportions of males and females injured. From these injured individuals only 9.8% of injuries judged to be of anthropogenic origin and 29.7% from attempted predation. Our study complements and correlates previous findings on this population that revealed strong site fidelity and low connectivity. The different characteristics of this population of reef manta rays also emphasize that concerns about species in New Caledonia are limited and that such favourable context needs to be preserved as reference for conservation.”

Photos and Infographics

Author Affiliations

  • UMR ENTROPIE-IRD-UR-UNC-CNRS-IFREMER

  • Conservation International New-Caledonia

  • The Manta Trust

  • Laboratory of Marine Biology and Ecology, Aquarium des Lagons

  • University of New Caledonia

Funded by

  • Keidanren Nature Conservation Fund (KNCF)

  • Southern Province of New Caledonia

  • Conservation International