Behaviour and Ecology of the Dugong, Dugong Dugon (Sirenia): Observations in Shoalwater and Cleveland Bays, Queensland.

Abstract

Dugongs (Dugong dugon) were studied in 2 bays in north Queensland from shore and small boats. Population in favoured areas of one bay was 5/km shoreline and 4 to 8% were juveniles. Feeding was the most common activity. The dugongs dived and grazed, apparently using their rostral disc to gouge a serpentine track through the bottom sediment. Removal of sea grass was calculated to be 78% from the tracks selected by observers or 59% from a random sample; both were thought to be underestimated. Dugongs tended to move on after 5 or 6 days when 30% of an area had been grazed. They left inshore sea grass beds before low tide to avoid being stranded, so their feeding was governed by the 25-h cycle of 2 high and 2 low tides daily. Inshore feeding was not restricted to hours of darkness. The most commonly eaten sea grasses were Zostera capricorni, Halophila decipiens and H. ovalis. From published work, it was thought that the dugongs specialized in whatever seagrass species were most readily available. Owing to opacity of the water, they could not be observed under water. Mean length of the 9 faecal pellets found on shore was 8.98 mm; the pellets included plant fibre.