Marine mammal diversity in the remote waters of Aldabra Atoll, southern Seychelles

Abstract

Aldabra atoll forms the furthest outer islands of the Seychelles archipelago. It is included in the large sanctuary for the Indian Ocean whales and due to its remote location is difficult to access. Few scientific investigations on marine mammals have been conducted here and we consequently still have a poor understanding of their dynamics and diversity. In the current study we report on marine mammal sightings that have been collected for the period 1973-2007 by field workers based at the Aldabra research station. These sightings were largely opportunistic and were both shoreand boat-based. In order to assess the diversity of marine mammals, either resident or transient, in Aldabra waters we compiled and quantified these records. Over the study period, 14 species of marine mammals have been reported (n=348 sightings). Among the more numerous sightings have been humpback whales (Megaptera novaeangliae, n=215), which are commonly seen during the months July-to-November and spinner dolphins that are seen year round. Throughout the study period, dugongs (Dugong dugon, n=28) have been seen at irregular intervals, mostly within Aldabra’s large lagoon. We briefly report on a dedicated effort during the 2007 humpback whale season to gain information on abundance and group characteristics.