Observations on an Aggregation of Grey Reef Sharks (Carcharhinus amblyrhynchos) in the Mozambique Channel Off the Coast of Nosy Be (Madagascar) and Tools for Photo-Identification—A New Aggregation Nursery Site?
by
, ,
Primo Micarelli
1,2,*
,
Marco Pireddu
3, 
Damiano Persia
4,
Marco Sanna
3,
Consuelo Vicariotto
1,
Antonio Pacifico
5,
Pietro Storelli
1,
Makenna Mahrer
6,
Emanuele Venanzi
7 and
Francesca Romana Reinero
1
1
Sharks Studies Center—Scientific Institute, 58024 Massa Marittima, Italy
2
Department of Physical Sciences, Earth and Environment, University of Siena, 53100 Siena, Italy
3
Department of Life and Environmental Sciences, University of Cagliari, 09126 Cagliari, Italy
4
Department of Life and Environmental Sciences, Polytechnic University of Marche, 60131 Ancona, Italy
5
Department of Economics and Law, University of Macerata, 62100 Macerata, Italy
6
W. M. Keck Science Department, Claremont McKenna College, Claremont, CA 91711, USA
7
Manta Diving Nosy Be, Nosy Be 207, Madagascar
*
Author to whom correspondence should be addressed.
Biology 2024, 13(9), 661; https://doi.org/10.3390/biology13090661
Submission received: 24 July 2024
/
Revised: 21 August 2024
/
Accepted: 23 August 2024
/
Published: 26 August 2024
(This article belongs to the Section Conservation Biology and Biodiversity)
Simple Summary
Between 2012 and 2023, using non-invasive photo-identification techniques, 23 specimens of grey reef sharks were identified in the Mozambique Channel off Nosy Be, in an area called “Mokarran”. Some specimens have been re-sighted in this area for up to 1982 days. A probable aggregation and nursery area for this species may have been identified off the coast of Madagascar and, if confirmed, it will be necessary to provide for its protection.
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.
