Shark Bay dugongs (Dugong dugon) in summer.: II:: Foragers in a Halodule-dominated community

Seasonal occurrence and behaviour of dugongs foraging on a monospecific meadow of Halodule uninervis were studied in a small cove at the mouth of the Wooramel delta in eastern Shark Bay. Dugongs appeared in numbers in the habitat only in late summer, coincident with peak rhizome productivity, and foraged exclusively by rooting into the substratum. Foraging was nearly continuous through the daylight hours and at least some foraging occurred at night. Observations implied much higher seagrass consumption than has been reported for dugongs in captivity. Because Halodule leaves are fragile and much leaf material is lost to drift, dugongs foraged effectively only for rhizomes and selected for a diet rich in readily digestible carbohydrates. Dugongs foraged in cohesive groups of larger ave;rage size than elsewhere in the Bay and moved freely about the Cove without any evidence of territoriality. A majority of known females were accompanied by very small (presumably neonate) calves. Aggregation in a protected and energy-rich habitat, and a high rate of forage intake, are appropriate for lactating females with young and vulnerable calves. Cohesive groups mag consist of females and young. Fully adult males may tend to be solitary. Small areas dominated by tropical seagrasses appear important to dugongs in subtropical Shark Bay.