1. Investigating the Pathways of Marine Debris Found in the Arafura and Timor Seas David Griffin, CAWCR Ilse Kiessling, DEWHA 29 July 2008

2. Pathways of Marine Debris Marine debris – not easy to clean up

3. Pathways of Marine Debris Many thousands of tonnes of nets

4. Pathways of Marine Debris not just ugly

5. Pathways of Marine Debris

6. high concentrations: northern Gulf of Carpentaria

7. Pathways of Marine Debris Where does it come from? Sorry to disappoint – no clear answer has emerged but we’re better positioned now to find an answer

8. Pathways of Marine Debris White (2004) hypothesis

9. Pathways of Marine Debris New approach: use Bluelink 15-year 10km-res ocean model

10. Pathways of Marine Debris Release many items continuously for 1 year, follow them for another year. Repeat for many years.

11. Pathways of Marine Debris

16. Add wind*3% to 0-10m, daily average current

17. Pathways of Marine Debris

23. year after

24. Pathways of Marine Debris year before

25. Pathways of Marine Debris

28. How can you verify a model that is so complex? Its not easy. It can be correct for transient events, but wrong for the seasonal cycle, or vice-versa.

29. Pathways of Marine Debris Feb 0-10m

30. Pathways of Marine Debris May 0-10m

31. Pathways of Marine Debris Aug 0-10m

32. Pathways of Marine Debris Nov 0-10m

33. Pathways of Marine Debris

35. Conclusions Do nets move as per the model simulation? If so, the results suggest the nets must come from the Pacific. But few nets are found on the Great Barrier Reef possible explanations: the model has too much flow through Torres Strait or: the effect of the NW monsoon is under-estimated (wind model wrong, or near-surface shear under-estimated)

36. Pathways of Marine Debris Recommended future work include effect of tides on bottom drag determine drift characteristics of derelict nets validate model by releasing drifters in Arafura Sea re-check GBR for nets

37. Thank you Email: David.Griffin@csiro.au Web: www.cmar.csiro.au