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Dugongs in Japanese waters: an international perspective

Dugongs in Japanese waters: an international perspective

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Dugongs in Japanese waters: an international perspective

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  1. Dugongs in Japanese waters: an international perspective Helene Marsh James Cook University Australia Coordinator IUCN Dugong Action Plan

  2. The modern sirenia (seacows)- dugongs and manatees

  3. Biodiversity importance of Order Sirenia • Taxonomically unique • 2 families • Trichechidae • Antillean manatee Trichechus manatus • Amazonian manatee Trichechus inunguis • West African manatee Trichechus senegalensis • Dugongidae • Dugong Dugong dugon • Steller’s sea cow Hydrodamalis gigas

  4. Global conservation status of modern sirenia Antillean manatee vulnerable Amazonian manatee vulnerable West African manatee vulnerable Dugong vulnerable Steller’s sea cowextinct

  5. Distribution of extant sirenia

  6. Conservation significance of dugongs • One of only four members of order Sirenia • Only member of family Dugongidae • Only strictly marine herbivorous mammal • Largest population size (>100,000) and range of extant Sirenians

  7. Habitat partitioning: extant Sirenia • Dugong • strictly marine • coastal and estuarine • Antillean and West African manatees • coastal, estuarine and freshwater (may be dependent on access to freshwater) • Amazonian manatee • freshwater in Amazon River system All restricted to tropics and sub-tropics

  8. Dietary partitioning: modern Sirenia • Dugong • seagrass specialist, eats invertebrates at higher latitudeends of range • obligate bottom feeder • Manatees • generalist feeders on salt & freshwater vegetation • feed throughout water column • opportunistic omnivores • Steller’s sea cow • surface feeder on cold-water algae

  9. Dugong digging up seagrass like a bulldozer Conclusion: Seagrass conservation is essential to dugong conservation

  10. Movements • Dugong • >60 animals satellite tracked • most movements local • several animals made long-distance movements • longest movement ~800 km in few days

  11. Dugong Movements 8 7 6 5 Frequency 4 3 2 1 0 0-10 >640 >10-20 >20-40 >40-80 >80-160 >160-320 >320-640 Maximum movement Conclusion: Dugongs could travel from other parts of their range to Okinawa but would be expected to do so only rarely

  12. Preliminary information on genetics of female dugongs • Genetic types of female dugongs from Southeast Asia (Indonesia, Thailand, Philippines generally distinct from those from Australia) - overlap at Ashmore Reef between Australia and Timor • Two maternal lineages in Australian coastal waters - overlap in Torres Strait between Australia and Papua New Guinea • One Australian lineage also recorded from East Africa and the Arabian Gulf

  13. Dugong Life history • Lifespan < 70 yr • Age first breeding 6-17yr • Gestation period 13-15 mth • Calving interval > 2.5 yr • Lactation ~ 1.5 yr • Adult survivorship >95% • Max rate of increase < 5% • Sustainable harvest ~2%

  14. Conclusions • Rate of change in dugong numbers is very sensitive to changes in adult survivorship • The 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 - this reduces the level of mortality that is sustainable Dugong conservation MUST address the issues of habitat conservation AND mortality reduction

  15. Threats to dugongs- overview from 37 countries

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

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

  18. Hunting and poaching kill dugongs in at least 26 countries

  19. Propellors kill and maim manatees and some dugongs

  20. Evidence for dugong decline- 37 countries • Anecdotal evidence suggests that dugong numbers have declined in at least 17 countries and that dugongs are extinct in 3 more • No evidence of reduction in extent of range - reduction of area of occupancy within range • Situation particularly serious in East Africa, Indian region and parts of Southeast Asia • Quantitative evidence of decline available only for Queensland, Australia

  21. Trends in dugong numbers Qld Shark Control Program • • 50 • • 40 • • • 30 • • • • Total dugongs caught per year • • • 20 • • • • • • 10 • • • • • • • • • • • • • • • • • • 0 1960 1970 1980 1990 2000

  22. Response to dugong decline in Queensland, Australia • Moratorium on hunting on urban coast • 16 Dugong Protection Areas (6353 km2) • no gill-netting (red) • gill-netting with restrictions (yellow) • Restructuring of fishing industry - buyout of fishers

  23. 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

  24. Situation in Okinawa • Small isolated dugong population • Evidence of decline - dugongs now present only around Okinawa Island in contrast to former wide distribution in Nansei Shoto • Threatened by: • habitat loss and disturbance- exacerbated by proposed construction of offshore base • fishing mortality (trap nets and gill nets) These threats need to be addressed in the context of the best scientific information if the dugong is to be conserved