Distribution and Abundance of Dugongs in the Northern Great Barrier-Reef Marine Park

Abstract

In 1984 and 1985, dugongs were censused from the air at an overall sampling intensity of 9% over a total area of 31 288 km2 within the northern sections of the Great Barrier Reef Marine Park. Sightings were corrected for perception bias (the proportion of animals visible in the transect which are missed by observers), and availability bias (the proportion of animals that are invisible due to water turbidity) with survey-specific correction factors. There were no significant differences between population and density estimates obtained from repeat surveys of the same areas. The resultant population estimate (±s.e.) was 8110 ± 1073 dugongs at an overall density (± s.e.) of 0.26±0.03 km-2, a precision of 13%. Dugongs occurred up to 58 km offshore and in water up to 37 m deep. The highest density of animals was seen on coastal seagrass beds at depths of <5 m. Maps of density and distribution are given. The design and timing of future surveys is also discussed.