Holothuries d’intérêt commercial des récifs de l’archipel des Glorieuses (îles Éparses, France), canal du Mozambique : abondances, tailles et impact de la pêche illicite

Abstract

Commercial holothurians of the Glorieuses Archipelago (Eparses Islands, France), Mozambique Channel : abundances, sizes and impact of illegal fisheries. Due to their isolation, Eparses Islands provide a valuable opportunity to investigate biodiversity in the absence of anthropogenic influence. The Glorieuses Archipelago (11° 35’ S, 47° 18’ E) forms part of the Eparses Islands in the north of Mozambique Channel (Western Indian Ocean). The inventory and abundance assessment of the commercial holothurians (Echinodermata), were carried out in October 2015 as part of the PANAMAG (PAtrimoine NAturel MArin des Glorieuses) programme. Specimens were identified, photographed and measured in length, on the reef slopes at 22 sites down to 20 m, the inner slopes at 3 sites and the reef flats at 32 sites. Given the worldwide overexploitation of holothurians, it is important to know their present diversity and distribution in such remote areas. The commercial holothurians included 12 species in Glorieuses Islands. Their abundances are low in comparison with some other islands in the SWOI such as Mayotte and Réunion Island. Bohadschia atra is the most common and abundant, as in Mayotte and Banc du Geyser, with an average of 118 (± 60.6) individuals by hectare in the inner slopes. Measurements of the length of B. atra have shown that the individuals are smaller on reef flats and inner slopes and bigger on the reef slopes. Actinopyga miliaris was found for the first time in Glorieuses, however, Holothuria fuscogilva, species with high commercial value, has not been found since 2011. The abundances of holothurians are very low in the reef flats of Lys Island, particularly Holothuria nobilis (0.3 ind/ha ± 2.6) and Thelenota ananas (0 ind/ha). They are species with high commercial values and listed as “endangered” in the IUCN red list indicating an impact of the illegal fisheries in this area of the Glorieuses Islands. Of all the reef flats of the Glorieuses, Lys Island has the lowest abundance of B. atra, a species with medium commercial value. Thelenota ananas was not found on the reef slopes of Lys Island. Strong action is necessary to stop the illegal fisheries on Lys Island.