Assessing habitat damage caused by the grounding of the Shen Neng 1 on Douglas Shoal, southern Great Barrier Reef

The key methods employed to assess damage to Douglas Shoal were high-resolution multibeam sonar bathymetry coupled with towed video (Towvid) surveys. In combination, these methods provide high quality data to assess damage over the very broad area of reef impacted by the ship grounding.

Multibeam bathymetry is a form of echo sounding which uses pulses directed from the surface to the seafloor to measure the distance to the bottom by means of sound waves. Multibeam bathymetry and backscatter techniques are well suited to estimate areas of physical damage on coral reefs as they can detect flattening and gouging of the substratum as well as compacting of substratum expected following the grounding of large ships. Multibeam and backscatter techniques are best suited to detect physical damage on reefs with a relatively high degree of topographic complexity as this would provide the greatest contrast to reef flattened and/or gouged by a grounded vessel.

Towed video (Towvid) surveys of benthic habitats are well suited to conditions where diving is impractical or where large areas require survey. A strengthened underwater housing containing a digital video camera mounted on a sled is tethered to and towed behind the ship with electromechanical cable controlled by a winch. The imagery is automatically geo-referenced with GPS data and both are simultaneously recorded on miniDV tapes aboard the vessel. Towvid is effective in detecting gross physical damage to habitat and /or widespread mortality at a broad taxonomic level. It is also well suited to estimating physical habitat types but again within broad classifications.

Currents in the vicinity of Douglas Shoal were assessed using a satellite tracked drifter. The deployment of a satellite tracked drifter from the site of the grounding was to demonstrate the potential path of water-borne sediment plumes and oil spill contamination from shipping accidents at Douglas Shoal.

Passive samplers were deployed and water samples collected The deployment of and the collection of water to assess potential water contamination at Douglas Shoal. The analysis of these samples is currently underway at the National Research Centre for Environmental Toxicology (ENTOX).