Condition, Trends and Predicted Futures of Dugong Populations in the Great Barrier Reef World Heritage Area: Including an Evaluation of the Potential and Cost-Effectiveness of Indicators of the Status of These Populations
Other Publication ResearchOnline@JCUAbstract
The dugong (Dugong dugon) is the only strictly marine herbivorous mammal and the only member of the family Dugongidae. Dugongs and the three species of manatee are the only living species in the order Sirenia; one of three orders of mammals considered at significant risk of extinction at the ordinal level (Purvis et al. 2000). Dugongs can live for about 70 years, and reach a maximum size of between 2 – 3 m. Female dugongs have a minimum pre-reproductive period of between 6 – 17 yr (Marsh et al. 1984; Boyd et al. 1999; Kwan 2002) and a mean calving interval of between 2.4 – 7 yr. The age at first breeding and the time interval between calves is apparently dependent on the status of food supply (Boyd et al. 1999; Marsh and Kwan 2008). Dugongs are bottom feeders, and seagrasses are the most important component of their diet. Dugongs graze predominantly on intertidal and subtidal tropical and subtropical seagrass meadows, but are also known to feed on macro-invertebrates and algae. They feed on nine of the ten seagrass genera and on most of the species of seagrass that occur within their range (Green and Short 2003). Dugongs typically feed on several species of seagrass in mixed species seagrass meadows (Johnstone and Hudson 1981). The selection of seagrasses as food by dugongs is influenced by multiple factors including fibre, nitrogen and starch content and biomass (Lanyon and Sanson 2006); but as pointed out by Aragones et al. (2006), the nutritional basis for food selection by dugongs is poorly understood. Dugongs are found in the shallow, protected coastal waters of about 40 countries and territories in the tropical and subtropical Indian and Pacific Oceans. At a global scale, their distribution is characterised by relict populations separated by large areas where dugongs are believed to be close to extinction or extinct locally (Marsh et al. 2002). A recent synthesis suggests that dugongs are declining or locally extinct in at least a third of its range; of unknown status in nearly half; and possibly stable in the remainder (Marsh 2008). Dugongs are listed under the: IUCN Red List of Threatened Species as ‘Vulnerable’ to extinction; Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora 1973; and Appendix II of the Convention for Migratory Species of Wild Animals 1979.
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42
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Reef and Rainforest Research Centre
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Cairns, QLD, Australia
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