Observations on an Aggregation of Grey Reef Sharks (<i>Carcharhinus amblyrhynchos</i>) in the Mozambique Channel Off the Coast of Nosy Be (Madagascar) and Tools for Photo-Identification—A New Aggregation Nursery Site?

Abstract

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.

Keywords

• photo-identification
• Madagascar
• nursery
• shark aggregation
• <i>Carcharhinus amblyrhinchos</i>