IUCN Red List Assessment
Red List Category
Red List Criteria
The only reference site is the urban coast of Queensland where the most robust quantitative data on population trends are available and a 40 year time series of catch rates in nets set for bather protection indicates that the CPUE in 1999 was only 3% of that in 1962 (Marsh et al. 2005). This CPUE is considered an index of dugong decline in the region from all causes during this period. This decline and modern aerial survey estimates of dugong abundance were used to backcast the population in the region in the early 1960s (which would be expected to have been lower than that at the time of European settlement as a cottage commercial industry for dugong oil had existed at several locations along this coast since the 1850s. The extrapolation suggested that the region supported 72,000 (95% CI 31,000, 165,000) dugongs in the early 1960s compared with an estimated 4,220 (95% CI 2,360, 8,360) dugongs in the mid 1990s. The seagrass habitat in the region is currently insufficient to support 72,000 dugongs, a result which suggests that the habitat had also declined (unlikely) or that the shark net CPUE has overestimated the decline (see Marsh et al. 2005). If the magnitude of this decline was robust and typical of the entire range of the dugong, the dugong would qualify for being classified as Critically Endangered at a global scale.
As summarized in Table 2.1, the major causes of the dugong’s decline along the urban coast of Queensland are still present in most of the dugong’s range as follows: gill netting 87-99%, subsistence hunting 85-98%, human settlement 82-85%, agricultural pollution 80-89%. The magnitude of these threats is likely to be greater in most other parts of the dugong’s range than in Queensland. The Queensland coast supports a low human population density relative to most other parts of the dugong’s range and has a well developed system of marine parks and pro-active management. There is also anecdotal evidence that the area of occupancy of the dugong has declined in many parts of its range, especially along the coasts of east African and India where anecdotal evidence suggests that it is at high risk of extinction.
Even in the regions where we have classified the status of the dugong as stable, this classification is unconfirmed. Much of the northern Western Australian and some of the Northern Territory coast has never been surveyed for dugongs and there are no accurate estimates of the Indigenous harvest. The sustainability of this harvest must be questioned as it has been shown to be unsustainable by population modeling in remote parts of Queensland and Torres Strait (Heinsohn et al. 2004, Marsh et al. 2004).
Genetic information on dugong stocks is limited. Recent work based on mitochondrial DNA and microsatellite markers (Brenda McDonald, unpublished data) indicates that the Australian dugong population is not panmictic. There is clear evidence of two maternal lineages, which have a geographical basis apparently reflecting the existence of the Torres Strait land bridge between Australia and PNG, despite the flooding of this land bridge some six thousand years ago. The Australian dugong population still has a fair degree of genetic diversity indicating that recent losses are not yet reflected in the genetic makeup of the population. There is some evidence of gene flow between dugongs in Australia and Eastern Indonesia.
To date, there has been little effective management intervention to reduce anthropogenic impacts on the dugong, apart from legislative protection which is almost ubiquitous throughout its range. Management plans have been developed for some 22-24% of the range (mainly in Australia) but are in place in only 18-22% of the range. The dugong is protected by marine protected areas in 22-23% of its range (again mostly in Australia) (see Table 1.3 in attached PDF).
Because of the uncertainty associated with the assessment of the status of the dugong both on the Queensland coast based on the CPUE data (Marsh et al. 2005) and the rest of its range, we suggest that the classification should remain as Vulnerable A2bcd.
Follow the link below to see the tables referred to in the text.
- 2006Vulnerable(IUCN 2006)
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
- 1982Vulnerable(Thornback and Jenkins 1982)