Dugong abundance and distribution in the Bazaruto Archipelago, Mozambique

Despite the distribution of dugongs Dugong dugon ranging across nearshore waters of the tropical and subtropical regions of the Indian Ocean and western Pacific Ocean, their distribution in the western Indian Ocean is highly fragmented and appears to be declining. The population of the Bazaruto Archipelago is believed to comprise the only viable population in the region. In all, 27 surveys were flown over the Bazaruto Bay area to define the distribution and estimate the abundance of the species in the area. A total of 9 052 nautical miles of survey effort was flown during the surveys, from which there were 355 sightings of 760 dugongs. Two core areas of distribution were apparent within the surveyed area; a northern core area spread within the 10 m isobath between the Save River mouth and Ponta Bartolomeu Dias (21 degrees 24' S), and a southern core area aligned with the shallow sandbanks to the north and south of Santa Carolina Island. Group sizes recorded in the Bazaruto Archipelago were comparable to group sizes recorded in other regions where dugongs occur, although few large (>20) groups of dugongs were seen in this study. Line transect analyses of each survey showed dugong densities were considerably lower than densities recorded in surveys in Australian waters or in the Arabian Gulf, with a population estimate of 247 dugongs (CV = 34.1) when all surveys were considered, and 359 dugongs (CV = 38.2) when only the surveys that were carried out under adequate sighting conditions were included.