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Dugong

Dugong dugon

 

Dugongs (Dugong dugon) are herbivorous marine mammals found in tropical and subtropical waters of the Indian and Pacific oceans, from eastern Africa to the coast of Australia. Today, dugong numbers are reduced to isolated relict populations throughout much of the species’ historic range. (1,2,3) The world’s largest dugong population is found off Australia’s northern coast, while the second largest population resides in the Arabian Gulf. (1,4) Dugongs are a CITES Appendix I species, and are classified as vulnerable to extinction under the IUCN Red List of threatened species. (3)

Dugongs are a long lived, late maturing species with a maximum population growth rate estimated at only 5%. (1,5). They prefer to forage on seagrasses of families Potamogetonaceae and Hydrocharitaceae, which are most abundant in shallow, protected waters. (1) Their life history traits, along with their nearshore foraging habits, leave dugongs particularly susceptible to the effects of human activities in coastal waters. (1,2) Drowning caused by entanglement with fishing gear is a leading cause of adult mortality throughout the dugong’s range. (1) These encounters are likely to occur in shallow areas such as intertidal seagrass meadows, which fishermen and foraging dugongs can only access during high tides. (2,6) Other high-risk areas include narrow movement “corridors” such as tidal rivers and rocky headlands. (6)

Dugongs are most likely to come into contact with artisinal or subsistence operations utilizing gill nets, small mesh seines, traps and weirs. (2) They may also encounter larger-scale fishing gear such as drift gill nets, pushnets, trawls, purse seines, and longlines (2) The cumulative impact of these many small fisheries is difficult to assess due to incomplete data coverage. Bycatch data is sparse for Thailand, China, East Africa, India and Sri Lanka, Cambodia, Vietnam, Indonesia, and many Pacific Islands. (2) It can be difficult to attribute dugong mortality to fishing gear because even when dugongs are captured alive, fishermen have strong incentives to kill the animals for their valuable meat and body parts. Directed dugong fisheries persist in some areas, including an indigenous fishery in the Torres Strait between Australia and Papua New Guinea. (7,8)

Insufficient data on bycatch-related strandings is a major barrier to coordinating conservation strategies on an international level. (2,3) The South Pacific Regional Environment Programme (SPREP), a regional organization representing the environmental interests of 21 South Pacific nations and territories, created a Dugong Action Plan (DAP) in 2003. (9) The Action Plan seeks to restore dugongs to their historic cultural and ecological prominence in the South Pacific by supporting research and collaboration between member countries. Although the SPREP Action Plan represents a step in the right direction, it fails to address mortality due to entanglement and incidental catch. (5) An effective long-term conservation strategy will need to focus on identifying and protecting healthy populations and their habitat, while minimizing incidental mortality of adult dugongs.


Works Cited

1. Marsh, H., C. Eros, P. Corkeron, and B. Breen. 1999. A conservation strategy for dugongs: implications of Australian research. Marine and Freshwater Research 50: 979-990

2. Marsh, H., H. Penrose, C. Eros, and J. Hugues. 2002. Dugong: Status reports and action plan for countries and territories. UNEP/DEWA/RS.02-1

3. Marsh, H. 2006. Dugong dugon. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 01 July 2007.

4. Preen, A. 2004. Distribution, abundance and conservation status of dugongs and dolphins in the southern and western Arabian Gulf. Biological Conservation 118: 205-218

5. Gillespie, A. 2005. The dugong action plan for the South Pacific: An evaluation based on the need for international and regional conservation of sirenians. Ocean Development & International Law 36:135-158

6. Marsh, H. 2000. Evaluating management initiatives aimed at reducing the mortality of dugongs in gill and mesh nets in the Great Barrier Reef World Heritage Area. Marine Mammal Science 16(3): 684-694

7. Heinsohn, R., R.C. Lacy, D.B. Lindenmayer, H. Marsh, D. Kwan, and I.R. Lawler. 2004. Unsustainable harvest of dugongs in Torres Strait and Cape York (Australia) waters: two case studies using population viability analysis. Animal Conservation 7:417-425

8. Marsh, H., I.R. Lawler, D. Kwan, S. Delean, K. Pollock and M. Alldredge. 2004. Aerial surveys and the potential biological removal technique indicate that the Torres Strait dugong fishery is unsustainable. Animal Conservation 7:435-443

9. South Pacific Regional Environment Programme. 2002. Regional Marine Species Programme Framework. Dugong Action Plan.

Available at <http://www.sprep.org/yost/pdfs/SPREPMarSpecActionPlans2003-07.pdf>