Threatened Species: Dugong

Dugongs are marine mammals common in tropical coasts of East Africa, through south and southeast Asia all the way to Australia. Its body shape is similar to a pregnant lady which led to the idea of the presence of mermaids in the sea. But of course, that is not true. Dugong dugon belongs to the Sirenia order and it is the remaining species in the Dugongidae family. They are herbivorous animals, mainly focusing on specific seagrass species or marine algae if seagrass are scarce, so they are usually found grazing at the seagrass beds (Gales et al. 2003; Marsh et al. 1982). Having low birth rate and late sexual maturity, their population is vulnerable to disturbances (Hines et al. 2005). Large amount of energy is spent on raising their single offspring making them a good representative of consummate K-selectors (Pianka 1970). Little is known about this marine mammal because of their sensitive and shy character, most of the time avoiding places with human activities (Hutomo & Moosa 2005).






The habitat of dugongs is usually seagrass beds located in protected warm shallow waters of 1 meter or more. These areas can provide them food, protection from predators, large waves and storms and also a suitable place for calving (Heinsohn & Spain 1979). They are common along coastal areas but can also be found in deeper waters if the continental shelf is wide just like the Sunda shelf of SEA. Their grazing activities influence the species composition of the seagrass community. This may lead to an increased productivity of the seagrass community (Fortes 1988). Their distribution and population varies in each country of SEA. In Thailand, dugongs are mostly found near islands off the Andaman coast, while in Vietnam and Cambodia, there is speculation that a small population of them are moving between these two countries and the Can Dao National Park (Beasley & Davidson 2007; Hines et al. 2005). In some part of Myanmar, the dugong population is healthy due to less threat from human (Ilangakoon & Tun 2007). For the Philippines and Indonesia, surveys have found dugong population to be scattered around the islands and included that Indonesia is an important refuge for the population (Hutomo & Moosa 2005). In 1994, the estimated population was about 1000 in Indonesia. As for Malaysia, Singapore and Brunei, dugongs were noticed in the coast of Sabah and Sarawak but mostly in Sabah, east coast of peninsular Malaysia, waters of Langkawi Island and the Johor-Singapore region (Beasley & Jefferson 1997).



The conservation status of the dugong is classified as vulnerable by the World Conservation Union based on the declining numbers, declined habitat quality and the potential of it to be exploited to an unsustainable level (Hines et al. 2005). This mean that all trades and products of this species are prohibited (Ilangakoon & Tun 2007). In Southeast Asia (SEA), their numbers has been decreasing due to three major factors which are direct hunting, by-catch and habitat degradation. Due to these threats, SEA countries are concern with the dwindling numbers so most of these countries are making an effort to conserve the present population.



By-catch poses a major threat to the dugong population. This occurs because of the use of illegal fishing techniques such as high intensity trawling (Robert & Hawkins 1999). Trapped dugongs do not get released but instead killed and sold or consumed for countries such as Thailand. They believe that the body parts of dugongs have high medicinal values, can be used as an aphrodisiac and the bones are used to ward off bad luck (Hines et al. 2005). Even with their protection status, the dugongs are hunted as their tusk can be sold up to $USD 100. The high demand for dugongs led to another major threat which is direct hunting for dugongs in countries which associates dugongs with strong traditional beliefs. Even if fishing communities uses legal fishing methods, dugongs and other marine mammals still get caught in fishing nets. The marine mammals die from the entanglement of the nets because the nets were left for 1 or 2 days before they are being recovered which can be avoided if they were released immediately (Duarte 2002). Declined in water quality are also affecting the population of the dugongs as it degrades and fragment their habitat. The water quality is affected by chemical pollution from pesticides and waste released into the ocean and also the development of coastal areas releasing excessive sediments making the water turbid (Delgado et al. 1997; Jackson et al. 2001).



Management of the dugong population can only be carried out if more information about their distribution and population are known to locate areas that are still supporting a significant amount of them (Marsh et al. 2002). With this information, a regional agreement and cooperation is needed to create inter-regional protected marine parks because dugongs are migratory mammals (Department of the Environment, Water, Heritage and the Arts, Australia). It is important that these marine protected areas include seagrass beds besides corals and it should involve large areas. It is also crucial to have NGOs and local fishers to be involved to monitor the populations at the coastal zones and also protect the dugong numbers to form an integrated coastal zone management. This can be done together with the effort of giving public awareness to the locals about conservation of dugongs and other marine animals (Marsh et al. 2002).



Restoring and protecting mangrove forest can also help because mangroves provide a major source of nutrient to the seagrass bed (Low et al. 1994). To prevent water pollution in these sensitive areas, an environmental impact assessment has to be conducted especially for projects such as aquaculture, land reclamation and port construction. All these activities contribute to a large percentage of a reduced in water quality of the seagrass bed areas. Illegal methods of fishing should be stopped because trawling destroy seabed by ripping the grass of the seabed (Marsh et al. 2002). Acoustic alarms has also been used to signal of there is any trapped large animals in the fishing nets and has largely reduced the number of marine mammal deaths (Kraus et al. 1997). As for direct hunting of these mammals, it is important to realize the driving force of this doing which is poverty. This can be reduced by providing more alternative source of income to reduce poverty. Lastly, in order for all these strategies to work, strict laws and consistently strong law enforcement should be in place, if not all these strategies would just go to waste (Hines et al. 2005).


The conclusion of this is that many factors contribute to the reducing numbers of dugongs but it can be overcome with the effort of every individual to protect this species

References
Beasley, I. and Jefferson, T. A. (1997) Marine mammals of Borneo: a preliminary checklist, Sarawak Museum Journal 51, pp. 193–210.
Beasley, I. L. and Davidson, P. J. A. (2007) Conservation Status of Marine Mammals in Cambodian Waters, Including Seven New Cetacean Records of Occurrence, Aquatic Mammals 33, pp. 368-379.
Delgado, O. et al. (1997) Seagrass regression caused by fish cultures in Fornells Bay, Menorca, western Mediterranean, Oceanologica Acta 20, pp. 557–63.
Department of the Environment, Water, Heritage and the Arts, Australia, Marine species conservation, http://www.environment.gov.au/coasts/species/dugongs/index.html Date accessed: 1 October 2010.
Duarte, C.M. (1995) Submerged aquatic vegetation in relation to different nutrient regimes, Ophelia 41, pp. 87–112.
Duarte, C. M (2002) The future of seagrass meadows, Environmental Conservation 29, pp. 192–206.
Fortes, M. D. (1988) Mangrove and Seagrass Beds of East Asia: Habitats under Stress,
Royal Swedish Academy of Sciences 17, pp. 207-213.
Gales, N. et al. (2003) Marine Mammals: Fisheries, Tourism and Management Issues, Tasmania, CSIRO PUBLISHING, pp. 1-19.
Heinsohn, G.E. and Spain, A.V. (1974) Effects of a tropical cyclone on littoral and sub-littoral biotic communities and on a population of dugongs (Dugong dugon), Biological Conservation 6, pp. 143-152.
Hines, E. et al. (2005) Community Perspectives and Conservation Needs for Dugongs (Dugong dugon) Along the Andaman Coast of Thailand, Environmental Management 36, pp. 654–664.
Hutomo, M. and Moosa, M. K. (2005) Indonesian marine and coastal biodiversity: present status, Indian Journal of Marine Sciences 34, pp. 88-97.
Ilangakoon, A. D. And Tun, T. (2007) Rediscovering the dugong (Dugong dugon) in Myanmar and the capacity building for research and conservation, The Raffles Bulletin of Zoology 55, pp. 195-199.
Jackson, J.B.C. et al. (2001) Historical overfishing and the recent collapse of coastal ecosystems, Science 293, pp. 629–638.
Kraus, S. et al. (1997) Acoustic alarms reduce
porpoise mortality, Nature 388, pp. 525.
Low, J. K. Y. et al. (1994) Mangroves as a habitat for endangered species and biodiversity conservation, Proceedings Third ASEAN-Australian Symposium on Living Coastal Resources Status Review, Chulalongkorn University 1, pp. 157-169.
Marsh, H. et al. (1982) Analysis of stomach contents of dugongs from Queensland, Australian Wildlife Research 9, pp. 55-67.
Marsh, H. et al. (2002) Dugong: status report and action plans for countries and territories, United Nations Environment Programme, pp. 52-83.
Pianka, E. R. (1970) On R and K selection, American Naturalist 104, pp. 592-597.
Roberts, C. M. and Hawkins. J. P. (1999) Extinction risk in the sea, Trends in Ecology and Evolution 14, pp. 241–246.