Photoidentification as a complementary tool to evaluate whale shark movements between different areas: the case of Nosy Be in Madagascar and the Gulf of Tadjoura in Djibouti

The whale shark Rhincodon typus, the world’s largest fish, is highly mobile, and is capable of migrating for thousands of kilometers each year. According to the IUCN Red List, areas where 500 or more individuals have been documented through either counts or model estimates include the Arabian Gulf and Gulf of Oman, Ningaloo Reef in Western Australia, Darwin Island in the Galapagos, Quintana Roo in Mexico, Inhambane province in Mozambique, Philippines, and Mahe in the Seychelles (Pierce & Norman, 2016). However, information on the global population structure and movement patterns remains limited. Recently, the whale shark population in Madagascar has been estimated at more than 400 individuals (Diamant et al., 2021), while in Djibouti at about 190 individuals (Boldrocchi et al., 2020). The aim of the study is to compare in the long term the two populations with a non-invasive system of identification of individual specimens, the I3S Classic program, to evaluate the possible presence of movements of individuals between these two areas.