Early on the morning of 7 January 2003, a large empty yellow plastic quarantine bag was found on the high tide mark of Wooli Beach, New South Wales, Australia. These heavy duty plastic bags are used for storage of items that pose a quarantine risk and are sealed on board ships by Quarantine Inspectors. As the disposal of plastic at sea is prohibited, the Australian Maritime Safety Authority (AMSA) undertook an investigation to determine the source of the bag. A suspect ship was identified, and AMSA inspectors boarded the ship and obtained documentation that confirmed eight days earlier the ship had travelled past Wooli Beach some 514 kilometres offshore. To assist AMSA, Asia-Pacific ASA performed a series of SARMAP model simulations (backward and forward) to determine the trajectory of the bag and establish whether the ship identified was in fact responsible.
The backward tracking simulation demonstrated the bag moving seaward from Wooli Beach would intersect with the ships' path. To further understand the movement of the bag, a series of forward tracking simulations were carried out along the ships' recorded geographic positions. By simulating the release of the bag from selected positions, it was calculated that if the bag entered the sea between 17:30 hrs-19:30 hrs on the 29 December 2002, the bag would reach Wooli Beach by high tide the night of 6 January 2003. The figure to the left shows the predicted movement of the bag over the 8-days.
The findings from this modelling study formulated part of the evidence in a successful prosecution of the ships' Owners and Master during December 2004 for offences involving illegal disposal of plastic and food waste.
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