THE DISTRIBUTION AND ABUNDANCE OF THE DUGONG IN SHARK BAY, WESTERN-AUSTRALIA

In July 1989, dugongs were counted from the air at an overall sampling intensity of 7.9% over 14 239 km2 in Shark Bay, Western Australia. Co unts were corrected for perception bias (the proportion of dugongs vis ible in the transect that are missed by observers), and standardised f or availability bias (the proportion of animals invisible because of w ater turbidity) with survey-specific correction factors. The resultant minimum population estimate was 10 146 +/- 1665 (s.e.) dugongs at an overall density of 0.71 +/- 0.12 (s.e.) dugongs km-2, the highest dens ity ever recorded on a large-scale dugong survey. The proportion of ca lves (19%) was higher than for most other dugong surveys conducted in Shark Bay and elsewhere, suggesting an exceptionally high calving rate in 1988. Dugong density was highest (>5 km-2) in relatively deep wate r (12-16 m) in the eastern half of Shark Bay opposite the tip of Peron Peninsula and in the western Bay opposite the northern half of Dirk H artog Island. Fewer than 4% of dugongs sighted in Shark Bay during the survey were in waters colder than 18-degrees-C. Results of aerial sur veys over 906 km2 in the Faure Sill region of the eastern Bay in Novem ber 1990 and January 1991 suggest that between a third and a half of t he dugongs in Shark Bay are located in this region during the summer. In contrast, only one dugong was sighted there during the winter surve y. The survey confirms that Shark Bay is an internationally significan t dugong habitat.