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

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

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 

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

Variation between surveys: population size N N S

Constant hotspots within surveys: population desnity

Reasons for movements: large- scale seagrass dieback e.g 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

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

Impact of seagrass dieback 25 years before on age structure of females sampled Apparent Pregnancy Rate TS dugongs

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

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

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 Best estimate of catch ~1000

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