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

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

Pathways of Marine Debris Many thousands of tonnes of nets

Pathways of Marine Debris not just ugly

Pathways of Marine Debris

high concentrations: northern Gulf of Carpentaria

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

Pathways of Marine Debris White (2004) hypothesis

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

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

Pathways of Marine Debris

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

Pathways of Marine Debris

year after

Pathways of Marine Debris year before

Pathways of Marine Debris

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.

Pathways of Marine Debris Feb 0-10m

Pathways of Marine Debris May 0-10m

Pathways of Marine Debris Aug 0-10m

Pathways of Marine Debris Nov 0-10m

Pathways of Marine Debris

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)

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

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