Environmental assessment of potential marine farming areas in Macquarie Harbour Tasmania

An environmental assessment of nine areas in Macquarie Harbour in which marine farming zones may be located was conducted between the 17th and 21st of January 2011. The environmental assessment covered an area of approximately 2533.61 ha from the northwest of the Harbour, between Liberty Point and Sophia Point and to the southeast between Steadman Point and Coal Head. This survey describes the substrate type, habitat distribution, bathymetry, and benthic flora and fauna in the nine proposed zones. The primary substrate for all nine zones was silt. There were some seabed surface anomalies in the acoustic data in Zone 8 which were inconsistent with the standard acoustic signature for consolidated habitat and which appeared to be debris on the seafloor (e.g. tree logs or concrete moorings). The surface layer of the silt sediment was characterized by a coppery brown surface deposit followed by dark grey (generally not black) sediment below. At several sampling locations there were small lumps of more densely aggregated mud within the body of the main sediment. The majority of the sediment grabs showed no evidence of anoxia (visual or smell). The areas sampled ranged in depth from 10 m (Zone 9) to 50 m (Zone 2). The bathymetric range within each zone differed, but generally sloped towards the centre of the channel from the landward sides. Zone 6 and 7 both had their deepest margins in the centre of the proposed zones. Zone 8 showed no variation in bathymetry maintaining a consistent 16 m water depth. Large and small polychaete tubes were frequently observed on the surface of the sediment in the video footage. Other fauna observed included heart urchins, bait fish and flathead (Platycephalidae). Two skates were observed in the video footage from zone 3 (20m depth) but the images were not clear enough to determine whether this was the threatened Port Davey Skate (Zearaja maugeana).