Distribution and abundance of dugongs in Moreton Bay, Queensland, Australia

Abstract

Dugong abundances in Moreton Bay (south-east Queensland) were estimated during six bi-monthly aerial surveys throughout 1995. Sampling intensity ranged between 20 and 80% for different sampling zones within the Bay, with a mean intensity of 40.5%. Population estimates for dugongs were corrected for perception bias (the proportion of animals visible in the transect that were missed by observers), and standardised for availability bias (the proportion of animals that were invisible due to water turbidity) with survey and species-specific correction factors. Population estimates for dugongs in Moreton Bay ranged from 503 ± 64 (s.e.) in July to 1019 ± 166 in January. The highest uncorrected count was 857 dugongs in December. This is greater than previous population estimates, suggesting that either previous surveys have underestimated abundance and/or that this population may have increased through recruitment, immigration, or a combination of both. The high degree of variation in population estimates between surveys may be due to temporal differences in distribution and herding behaviour. In winter, dugongs were found in smaller herds and were dispersed over a wider area than in summer. The Eastern Banks region of the bay supported 80–98% of the dugong population at any one time. Within this region, there were several dugong 'hot spots' that were visited repeatedly by large herds. These 'hot spots' contained seagrass communities that were dominated by species that dugongs prefer to eat. The waters of Rous Channel, South Passage and nearby oceanic waters are also frequently inhabited by dugongs in the winter months. Dugongs in other parts of Moreton Bay were at much lower densities than on the Eastern Banks.