Survey on reef shark abundance in the Western Indian OceanPublished online in July 2012
Comparative abundance of reef sharks in the Western Indian Ocean
Chris Clarke, James Lea and Rupert Ormond
Surveys were conducted over a four year period to assess the abundance of sharks at various remote coral reefs in the Western Indian Ocean, including the Jeddah region of the Red Sea; the isolated islands of Bassas da India, Europa and Aldabra; and the southern three atolls of the Maldives. Two methods were used: direct observation (UVS) by SCUBA divers following chumming, and Baited Remote Underwater Videocameras (BRUVs). Combined these recorded some 795 sharks of 11 different species. Three findings were notable: i) in some locations, especially those receiving more effective protection, medium-sized sharks such as blacktip reef shark, Carcharhinus melanopterus, and grey reef shark, Carcharhinus amblyrhynchos, were relatively abundant, with the main species observed probably depending on habitat factors, such as the presence of extensive lagoons and channels; but ii) shark community composition varied considerably between areas, with for example blacktip reef shark being most abundant at Aldabra, and Galapagos shark, Carcharhinus galapagensis, most abundant at Bassas da India; nevertheless iii) in all locations the largest predatory sharks such as tiger shark, Galeocerdo cuvier, appeared either scarce or absent, potentially a consequence of their wide-ranging movements combined with shark fishing activities in adjacent areas.
Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 2012