1. Large-scale movements of dugongs: evidence, reasons and policy implications Helene Marsh, Ivan Lawler, Donna Kwan

2. Direct evidence for large- scale movements –>80 animals satellite tracked –most movements local –several animals made long-distance movements –longest movement ~600 km in few days

3. Movements of satellite- tracked dugongs –movements individualistic –2/5 moved >80km –1/5 moved >150km –3 animals covered >80% of coast 1500km 400km Shoalwater  Bay Cooktown  Townsville 

4. Aerial surveys: indirect evidence for movements Standardised technique –Standard survey design –Corrections for perception and availability bias –Strict ceiling on weather –Two aircraft minimize effects of movement within surveys - Large spatial scales (30,000 km 2) every 5 years –Different survey regions surveyed in different years Time series since mid 1980s for much of east coast of Qld

5. Variation between surveys: population size N N S

6. Constant hotspots within surveys: population desnity

7. Reasons for movements: large- scale seagrass dieback e.g. 1000 km 2 of seagrass lost in Hervey Bay after two floods and a cyclone. Similar diebacks recorded in pristine and remote areas in Qld and WA

8. Impact of dugong habitat loss in Hervey Bay 1992 When their habitat is lost dugongs: postpone breeding and starve or move Locations of dugong carcasses Date Dugong numbers

9. Impact of seagrass dieback 25 years before on age structure of females sampled 1998-99 Apparent Pregnancy Rate TS dugongs 1978-790.09+ 0.03 1979-80 0.19+ 0.06 1980-81 0.24+ 0.08 1998-99 0.38+ 0.06

10. Policy implications: zonal protection for persistent hotspots but need to spread risk Dugong protection areas

11. Policy implications: Indigenous catch quotas must recognize variability in size & potential rate of increase of target population

12. Policy implications: Population trends not reliable index of population status at local or regional scales except over long time periods: PBR provides more information Sustainable annual catch for Torres Strait using PBR 32-154 Best estimate of catch ~1000

13. Conclusions Dugong habitats are subject to intermittent large-scale diebacks even in remote and relatively pristine areas Large numbers of dugongs postpone breeding or move as a result This represent considerable policy challenge to managers