DISTRIBUTION AND ABUNDANCE OF DUGONGS, TURTLES, DOLPHINS AND OTHER MEGAFAUNA IN SHARK BAY, NINGALOO REEF AND EXMOUTH GULF, WESTERN-AUSTRALIA

Strip-transect aerial surveys of Shark Bay, Ningaloo Reef and Exmouth Gulf were conducted during the winters of 1989 and 1994. These surveys were designed primarily to estimate the abundance and distribution of dugongs, although they also allowed sea turtles and dolphins, and, to a lesser extent, whales, manta rays and whale sharks to be surveyed. Shark Bay contains a large population of dugongs that is of internatio nal significance. Estimates of approximately 10000 dugongs resulted fr om both surveys. The density of dugongs is the highest recorded in Aus tralia and the Middle East, where these surveys have been conducted. E xmouth Gulf and Ningaloo Reef are also important dugong habitats, each supporting in the order of 1000 dugongs. The estimated number of turt les in Shark Bay is comparable to the number in Exmouth Gulf plus Ning aloo Reef (7000-9000). The density of turtles in Ningaloo Reef and, to a lesser extent, Exmouth Gulf is exceptionally high compared with mos t other areas that have been surveyed by the same technique. Shark Bay supports a substantial population of bottlenose dolphins (2000-3000 m inimum estimate). Exmouth Gulf and Ningaloo Reef were not significant habitats for dolphins during the winter surveys. Substantial numbers o f whales (primarily humpbacks) and manta rays occur in northern and we stern Shark Bay in winter. Ningaloo Reef is an important area for whal e sharks and manta rays in autumn and winter. The Shark Bay Marine Par k excludes much of the winter habitats of the large vertebrate fauna o f Shark Bay. In 1989 and 1994, more than half of all the dugongs were seen outside the Marine Park (57.4 and 50.7%, respectively). Approxima tely one-third to one-half of turtles and dolphins were seen outside t he Marine Park (in 1989 and 1994 respectively: turtles, 43 and 27%; do lphins, 47 and 32%). Almost all the whales and most of the manta rays were seen outside the Marine Park. Expansion of the Shark Bay Marine P ark, to bring it into alignment with the marine section of the Shark B ay World Heritage Area, would facilitate the appropriate management of these populations. This would also simplify the State-Commonwealth co llaboration necessary to meet the obligations of World Heritage listin g. The coastal waters of Western Australia north of the surveyed area (over 6000 km of coastline) are relatively poorly known and surveys of their marine megafauna are required for wise planning and management.