Abstract

Martinique Island hosts an exceptional marine biodiversity, with 43 elasmobranchs species documented in its waters. Rays, as key species in the marine ecosystem, play a crucial role in the food web. However, little is currently known about these species in Martinique. This study aims to shed light on the ray populations frequenting the shallows of Fort-de-France Bay, through non-invasive monitoring techniques. Aerial and snorkelling surveys, along with environmental DNA analysis, were conducted from September 2020 to March 2021. A total of 38 flights covering eight systematic located transects were conducted and 130 km were swum. Three ray species were identified in the bay: Aetobatus narinari, Dasyatis americana (by visual observation) and Pteroplatytrygon violacea (by environmental DNA). All of these are listed on the IUCN Red List of Threatened Species. A. narinari was the most frequently observed species, with a total of 206 sightings recorded during the aerial surveys and observations were made on each flight. Detectability was estimated using distance sampling, with species included as a covariate. Abundance estimates varied by month, ranging from 7 to 26 individuals, with an average density of 3.4 (7%) individuals per km². Environmental parameters showed no significant impact on ray presence, with only water level and current strength affecting habitat availability. The study highlighted the exceptional richness of the bay of Fort-de-France, which is also an area where a large proportion of the island's economic activities are concentrated. It is therefore vital to implement protection and conservation measures for this key area.