Unvegetated Substrates
Unvegetated substrates were mapped under four main categories. These were identified as sand, hard sand, silty sand and silt.
Sand
Sand is often a commonly encountered unconsolidated substrate but is most common in high to semi-exposed environments. This category represents the coarser end of a scale of sediments from silt to sand. Sand is generally characterised by a distinct second echo on the sounder trace.
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Hard Sand
Hard sand refers to unconsolidated substrates containing elements that confound the sounder output causing the signal to appear either harder or rougher than would be expected from sand. There are several factors that lead to a substrate being classified as hard. These are defined as modifiers in the habitat classification and includes large grain size, shell matter (either whole shells or shell grit) or biological material.
The following list provides examples of modifiers that are included in this hard sand category.
Physical: Coarse sand/gravel, compacted sand, rippled sand, shell or shell grit in sediment
Biological: Burrows, seawhips, holothurians
Hard sand was common in and around seagrass beds indicating the possible presence of rhizoidal mats of the seagrass and associated organisms. It was also common on the seaward side of reefs indicating the presence of shells, detritus and organisms whose origin is dependent on the nearby reefs. The extensive areas of shelly substrate in high current areas in the D'Entrecasteaux Channel were characterised by a hard sand signature. On more exposed shores sand hardens up closer to shore, due to coarser grade sands produced by the sorting action of waves.
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Silty Sand
Silty sand is common in low exposure and sheltered waters. It broadly incorporates any sediment with a significant proportion of coarse 'sand' particles and 'fine' silt particles. Silty sand is characterised by a less distinct echo on the sounder trace.
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Silt
Silt substrate is only found in deeper sheltered bays or in the back of sheltered bays. This habitat category represents the finest unconsolidated substrate. Silt is characterised on the sounder by a lack of a second echo and often little scatter in the trace tail.
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