The global status of dugongs in the context of their biology

1. The global status of dugongs in the context of their biology Helene Marsh

2. Conservation Significance of Dugongs • Class: Mammalia • Order: Sirenia • Family: Dugongidae • Species: Dugong Dugong dugon • Steller’s sea cow Hydrodamalis gigas (extinct) • Family: Trichechidae • Species: Antillean manatee Trichechus manatus • Amazonian manatee Trichechus inunguis • West African manatee Trichechus senegalensis Only member of family Dugongidae All extant sirenians vulnerable to extinction

3. Conservation Significance of Dugongs • Only strictly marine herbivorous mammal • Largest population size (>100,000) and range of extant sirenians

4. Seagrass Specialists • Mouth specialised for bottom feeding • Remove all parts of plant (leaves and rhizomes) • Leave feeding trails and feeding plumes • Like nutritious new growth – possibly farming large areas when in large herds

5. Life History • Lifespan 70+ yrs • Age first breeding 6-17 yrs • Litter size 1 • Calving interval  2.5 yrs • Gestation period 13-15 months • Lactation ~ 1.5 yrs • Adult survivorship > 95% • Max rate of increase 5% • Sustainable harvest ~ 2%

6. If Vietnamese waters support only a small population e.g. 100 dugongs then ANY mortality from human causes is potentially unsustainable

7. Movements • Have tracked > 60 animals • Most movements local • Several animals made long-distance movements • Longest movement ~800 km in few days

8. 1500km Cooktown Townsville 280km Shoalwater  Bay Movements of satellite- tracked dugongs • Covered over 80% of coast • 1/3 moved linear distances >80km • 1/6 moved >150km • 42 dugongs tracked on the east coast • 5-551 days 400km

9. Preliminary information on genetics of female dugongs • Genetic types of female dugongs from Southeast Asia (Indonesia, Thailand, Philippines) generally distinct from those from Australia • Two partially overlapping maternal lineages in Australian coastal waters • Pattern reflects ancient separation due to sea level change with modern incomplete mixing • Dugongs colonise new areas only rarely • Males only may be moving and breeding

10. Main Conclusions from Biology • Rate of change in dugong numbers is very sensitive to changes in adult survivorship • Impact of mortality (drowning in nets, boat strikes, hunting) on dugongs is serious • When dugongs don’t have enough to eat because of habitat loss, they delay breeding or move - this reduces the level of mortality that is sustainable

11. Conclusions for Vietnam • Dugong conservation MUST address the issues of habitat conservation AND mortality reduction • Dugong conservation in Vietnam should be developed in consultation with neighbouring countries - China, Thailand and Cambodia

12. The Global Status of Dugongs • UNEP status report and action plan • Covers 37 countries of dugongs’ range

13. Methods • Evaluation based on published information and expert opinions of about 100 scientists and managers regarding 37 countries and territories in dugong’s range • Snowball sampling technique • Informants contacted 1997 - 2001 during process leading to development of global status and action plan • Information reviewed by 60 in-country experts.

14. Dugong catch per unit effort in shark control nets on the urban coast of Queensland Evidence for Decline • Numbers have declined in at least 21 countries • Dugongs are extinct in 3 island groups • No evidence of reduction in extent of range - reduction of area of occupancy within range

15. Threats to Dugongs:Overview From 37 Countries THREATNO. OF COUNTRIES Fishing mortality (gill netting) at least 35 Habitat loss / Degradation all Hunting / Poaching at least 16 (27?) Boat Impacts at least 11

16. Dugongs tangle in mesh nets and accidentally drown in many countries

17. Habitat loss, especially due to extreme weather events 1000 km2 of seagrass habitat were lost in Hervey Bay Queensland after two floods and a cyclone (hurricane)

18. Hunters and poachers kill dugongs in many countries Medical use of dugong products is a major reason for poaching and for killing animals which are caught accidentally in nets or fish traps

19. uncertain – likely extinction in Japan reasonable prospects for survival uncertain prospects for survival high risk of extinction uncertain – likely extinction in Palau high risk of extinction secure – except urban coast of Queensland

20. Prospects in SE Asia uncertain: likely extinction in Japan • Populations small and fragmented but cover vast areas with potential for recruitment from other areas • Pressure from gill-netting, dynamite fishing, habitat destruction, boat impacts and hunting likely to increase • Few effective conservation initiatives

21. Suggested approaches to dugong conservation • Identify areas that still support significant numbers of dugongs • Consider with extensive local involvement how dugong mortality can be minimised and their habitat protected • If possible, protect dugongs in the context of comprehensive plans for coastal zone management using the dugong as a flagship species