Observations of dugongs at Aldabra Atoll, western Indian Ocean: lagoon habitat mapping and spatial analysis of sighting records

Abstract

Until recently, it was thought that dugongs (Dugong dugon) were extinct in the Seychelles. However, a collection of sightings at Aldabra Atoll, a World Heritage Site in the Seychelles, has renewed interest in dugong distribution in the western Indian Ocean. This article consolidates the records of dugong sightings held in the Aldabra Research Station library and explores their spatial patterning. The locations of sightings (2001–2009) are plotted onto a high-resolution benthic habitat map of the Aldabra lagoon created by classifying a QuickBird satellite remote-sensing image in January 2009. A spatial cluster detection procedure is applied to point records of sightings to reveal a statistically significant cluster of sightings in the north-west of the lagoon, at Bras Monsieur Clairemont, suggesting a mutual co-existence of dugongs and seagrass beds. A habitat suitability model combines the point data set of dugong sightings within the continuous benthic habitat map and identifies the central western area as containing the most suitable habitat for dugong inside the Aldabra lagoon.

Keywords:

• Seychelles
• benthic habitat map
• remote sensing
• cluster analysis
• dugong
• habitat suitability

Acknowledgements

The lagoon mapping project January–February 2009 was a collaboration between CCRU, University of Cambridge and SIF, made possible in part by Environment Trust Fund, Seychelles, and through sponsorship by the Department of Geography, University of Cambridge. The authors would like to thank the staff of SIF, both on Mahé and on Aldabra, for their extensive help and logistical support and for providing archived sightings data. They are also grateful to their boat skipper, Joshua Adeline, Dr. Tom Spencer at the CCRU and Rodney Quatre and the Seychelles National Parks Authority for assistance. The satellite images for the lagoon mapping project were kindly donated by Lilian Pintea at The Jane Goodall Institute.