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Is dugong management on the urban coast of Queensland effective? Helene Marsh James Cook University.

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Presentation on theme: "Is dugong management on the urban coast of Queensland effective? Helene Marsh James Cook University."— Presentation transcript:

1 Is dugong management on the urban coast of Queensland effective? Helene Marsh James Cook University

2 High cultural values

3 High political value

4 Seagrass specialist

5 Long-lived, slow breeding Lifespan < 70 yr Age first breeding 6-17yr Calving interval yr Adult survival >95% p.a. Sustainable harvest ~2% Dugong tusk with growth layers

6 Consequences of dugong being long-lived slow breeder Size of dugong population Sustainable mortality from all causes ,000<13 10,000<130

7  44 of 72 satellite tracked dugongs moved >30km; 14>100km  All size/age/sex classes  Up to 500km in 12 days Moves across jurisdictions

8 Conclusions To be effective dugong management must address the issues of: –conserving the quality of critical habitats and –minimising dugong mortality and be co-ordinated across jurisdictions

9 Already seriously depleted The dugong by-catch in the shark nets declined at 8.7% per year for 40 years

10 Multiple threats Boat strikes Agricultural pollution Food/medicine/artefacts for subsistence Gill netting Coastal development

11 Speed limits and vessel lanes Net fisheries closures Marine park rezoning Effort reduction Water quality protection plans Numerous management interventions Hunting management Management plans National partnership TUMRAs Nailsma project

12 Is current dugong management effective from the perspective of species conservation ?

13 Standardised technique Time series since mid 1980s Many regions in Australia Large spatial scales ~30,000 km 2 Measuring management effectiveness using aerial surveys

14 The probability of detecting a group of dugongs in an aerial survey is made up of 3 processes P [animal detected] = P[area sampled] * P[animal available] * P [ animal detected given it is available]

15 Dugong models fitted with dive computers raised from the bottom until visible from helicopter at aerial survey height in waters of various turbidities and sea states etc Estimation P [animal available to be seen] Data on distance below surface at which dugongs available under various conditions Dugong model

16 Zone of non-availability Dive profiles measured for wild dugongs fitted with dive computers 40,000 dives from 15 dugongs  Dive data + data from models allow estimation of P[animal available] for various environmental conditions

17 Estimate of P[animal detected given animal available] Done internal to the aerial survey using two independent observers and a mark recapture model X 11 - no. detected by both observers X 10 - no. detected by mid observer only X 01 - no. detected by rear observer only  P group being missed Aircraft seating

18 Overall results Moreton Bay- Hervey Bay

19 Overall results: southern border of GBRMP to Bowen

20 Overall results: Upstart Bay to Hinchinbrook

21 Overall results: urban coast

22 Is management successful ? – Depends on objective population maintenance or recovery? Recovery x ? Maintenance√

23 Sustainable human-caused mortality on urban coast -Cooktown to Coolangatta ObjectiveSustainable # dugongs p.a. Recovery 3-15 Maintenance GBR 6-57 Mortality target depends on management objective

24 Initiatives must reduce mortality and protect critical habitats Need clear management objectives and priorities Cross-TUMRA co-ordination essential Conclusions

25 Thanks Funding AFMA ARC CRC Reef Research GBRMPA JCU Pew Foundation SWRRFI MTSRF Contributions to the Research Amanda Hodgson Donna Kwan Ivan Lawler Guido Parra Tony Preen James Sheppard


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