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

Seasonal occurrence and behaviour of dugongs foraging on a monospecific mea dow 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 hab itat only in late summer, coincident with peak rhizome productivity, and fo raged exclusively by rooting into the substratum. Foraging was nearly conti nuous through the daylight hours and at least some foraging occurred at nig ht. Observations implied much higher seagrass consumption than has been rep orted for dugongs in captivity. Because Halodule leaves are fragile and muc h leaf material is lost to drift, dugongs foraged effectively only for rhiz omes and selected for a diet rich in readily digestible carbohydrates. Dugo ngs foraged in cohesive groups of larger ave;rage size than elsewhere in th e Bay and moved freely about the Cove without any evidence of territorialit y. A majority of known females were accompanied by very small (presumably n eonate) calves. Aggregation in a protected and energy-rich habitat, and a h igh rate of forage intake, are appropriate for lactating females with young and vulnerable calves. Cohesive groups mag consist of females and young. F ully adult males may tend to be solitary. Small areas dominated by tropical seagrasses appear important to dugongs in subtropical Shark Bay.