Global threatening processes
Dugongs are vulnerable to anthropogenic influences because of their life history and their association with seagrasses that are restricted to coastal habitats, and which are often under pressure from human activities. The rate of population change is most sensitive to changes in adult survivorship. Even a slight reduction in adult survivorship as a result of habitat loss, disease, hunting or incidental drowning in nets, can cause a chronic decline in a dugong population.
Habitat Loss and Degradation
Seagrass ecosystems are very sensitive to human influence (Fonseca 1987; Shepherd et al. 1989; Poiner & Peterken 1996). Seagrass beds may be destroyed directly by mining and trawling (Silas & Bastion-Fernando 1985), or lost through the effects of disturbances such as dredging, inland and coastal clearing, and land reclamation. These activities cause increases in sedimentation and turbidity which, in turn, lead to degradation through smothering and lack of light. Other threats include sewage, detergents, heavy metals, hypersaline water from desalination plants and other waste products. Most losses, both natural and anthropogenic, are attributed to reduced light intensity due to sedimentation and/or increased epiphytic growth
caused by nutrient enrichment. In some cases, factors such as poor catchment management and sediment instability interact to make the processes more complex so that it is often difficult to separate natural and anthropogenic causes of seagrass loss.
Accidental entangling in gill and mesh nets or traps set by fishers is considered a major, but largely unquantified, cause of dugong mortality in many countries (Perrin et al. 1996). In relatively shallow bays with large tidal fluctuations and high turbidity, seagrass meadows are largely intertidal. In such circumstances, dugongs and netters are all forced to use intertidal areas on the high tide, increasing the chances that dugongs will be caught.
Indigenous Use and Hunting
Dugongs are culturally significant to communities throughout their range. Dugongs are caught for meat, oil, medicaments, amulets and other products. In many countries dugong hunting is now banned and animals are no longer hunted deliberately, however, dugong products from indirect takes are still highly valued.
Information taken from Marsh, H., Penrose, H., Eros, C. & Hugues, J., 2002. Dugong: status reports and action plans for countries and territories. . In Early warning and assessment report series, (ed. UNEP).