The dugong: a conservation challenge

1. The dugong: a conservation challenge Helene Marsh and associates

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

3. Biodiversity importance of Order Sirenia • 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 modern 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. Long-lived, slow breeding • 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%

9. Dugong feeding trail

10. Seagrass specialists- coastal distribution, pollution, fishing mortality and boat strike

11. Restricted coastal habitat subject to large-scale diebacks e.g. 1000 km2 of seagrass habitat were lost in Hervey Bay Queensland after two floods and a cyclone but also in several pristine and remote areas

12. Preliminary information on genetics of female dugongs : mitochondrial DNA • Mitochondrial DNA of dugongs from Southeast Asia generally distinct from those from Australia • Two maternal lineages in Australian coastal waters - overlap in Torres Strait between Australia and Papua New Guinea • High haplotypic (h=0.97)and nucleotide (=2.3) diversity • No data from Pacific Islands

13. Australian lineages reflect sea level changes

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

15. 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 • Individual movements variable even for animals caught together 400km

16. Dugongs visible from aircraft

17. Objective of aerial surveys: To monitor dugong distribution & relative abundance over large spatial and temporal scales Standardised technique Time series since mid 1980s • Corrections for bias • Strict ceiling on weather • Conducted over large spatial scales (30,000 km2) every 5 years since mid 1980s • Different survey regions surveyed in different years

18. Water turbidity affects dugong sightability

19. Correction for animals which can’t be seen in turbid water Models fitted with timed depth recorders were raised from the bottom until they become visible from a helicopter at aerial survey height

20. Dugong dive profiles Zone of non-availability ~40,000 dives from 15 dugongs Estimation of the proportion of dugongs missed in water of varying turbidity: estimates of absolute abundance

21. Changes in dugong numbers in Hervey Bay Queensland Location of blocks and transects in Hervey Bay ~2000 dugongs

22. Similar patterns of large scale movement • Torres Strait • Cape York coast of Great Barrier Reef • Urban coast of Great Barrier Reef • Shark Bay – Exmouth Gulf in Western Australia

23. Conclusion: Aerial surveys are excellent for: determining dugong distribution and relative abundance But not for monitoring population change in Australia ? New Caledonia

24. Monitoring change over 40 years using CPUE • In 1962, the Queensland government began • the Shark Control Program aimed at reducing • shark numbers at popular bathing beaches • Nets used to catch sharks also catch marine • mammals including dugongs • Analysed temporal changes in the dugong • catch per beach from 1962-99 as an index • of changes in dugong abundance • (in response to ALL influences)

25. Location of shark meshing contract areas

26. Assumptions • Netting practice did not change  • Catch rate of dugongs was proportional • to population size ?  • Dugongs did not learn to avoid nets ?  • Dugongs were not alienated from netted beaches • by human use ???

27. The dugong by-catch declined at 8.7% p.a.

28. Conclusion If assumptions are correct, dugongs numbers on the urban coast of Qld in the local regions of the shark nets have declined to about 3% of their 1960 value

29. Response to dugong decline in Queensland • 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

30. THE BLIMP-CAM • Tethered helium filled blimp/balloon • Mounted remote control video camera • Monitor on boat to view video image • Digital video recorder on boat BEHAVIOURAL DATA Individual behaviour & herd behaviour - ethogram and time budget - dive and surfacing times - mother/calf interactions - herd size, composition, relative orientation & effects of habitat Dugong behaviour from a blimp-mounted video camera

31. OBJECTIVE • To determine the effects of boat noise on dugong behaviour • opportunistically • controlled experiments • PRELIMINARY RESULTS: • Response is slow, particularly to boats going fast - may be run over before having time to move • Dugongs usually move up to 3-400 m away and resume their original activity

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

33. Evidence for dugong decline- 37 countries • Anecdotal evidence suggests that dugong numbers have declined in at least 21 countries and that dugongs are extinct in 3 island groups • No evidence of reduction in extent of range - reduction of area of occupancy within range • Quantitative evidence of decline available only for Queensland, Australia

34. Multiple impacts Boat strikes Habitat loss from terrestrial runoff Net entanglements

35. Threats to dugongs- overview from 37 countries

36. High risk of extinction • Populations apparently small and fragmented • Pressure from gill-netting, shark meshing, dynamite fishing and habitat destruction • Few effective conservation initiatives

37. Reasonable prospects for survival • Significant numbers of dugongs • Human population density and coastal impacts low in some areas

38. Uncertain: likely extinction in Japan • Populations small and fragmented. • Japanese population extremely small and isolated and subject to habitat loss and fishing impacts • Pressure from gill-netting, dynamite fishing, habitat destruction, boat impacts and hunting likely to increase • Few effective conservation initiatives

39. Probably secure except for urban coast and some heavily hunted areas • Region supports large numbers of dugongs (estimated 85,000) • Remote: human population density and coastal impacts generally low • Population changes confounded by large-scale movements • Active conservation initiatives, including dugong-specific actions in Great Barrier Reef region

40. Pacific Islands: Uncertain future • Populations apparently mostly small and fragmented. • Potential for recruitment from other areas uncertain • Pressures likely to increase • Few conservation initiatives • New Caledonia very important

41. Conclusions • Total global population ~ 100,000 dugongs • Long-lived slow breeding • Seagrass specialist • Declines in most parts of range – multiple impacts • New Caledonia with significant, relatively undisturbed lagoonal seagrass habitats and no gill netting - important for dugong conservation near eastern limit of range • New Caledonia dugongs special -use reefal habitats, including outer edge of barrier reef

42. 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 (hunting/poaching in New Caledonia) 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