Marine Produce Australia: Cone Bay Barramundi Aquaculture ...

efore smoothly decreasing to zero again and that the interval between low and
high tides is approximately six hours. The rule states that in the first hour after low
tide the water level will rise by one twelfth of the range, in the second hour two
twelfths, and so on according to the sequence - 1:2:3:3:2:1. The rule, as generally
applied, assumes that the period between high and low tides is six hours. For this
project, the period varied between 5.3 and 7.2 hours. To improve accuracy, the rule
was modified such that the water level is assumed to rise by one twelfth of the
range during the first one sixth of the period between tides (approximately an hour),
rather than during the first hour (precisely), and similarly for the remaining five
sixths of the period between tides. In addition, a further offset of 0.5 m, consistent
across the entire dataset, was added to the depth to account for the depth of the
transceiver below the water. The rule of twelfths and transceiver depth corrections
were calculated using a custom VBA Excel Macro.
Table 2 Tide predictions for Derby (www.transport.wa.gov.au)
Saturday 22nd Oct 2011 3.95m @ 1:46 AM
8.31m @ 7:38 AM
3.76m @ 2:31 PM
8.14m @ 8:52 PM
Sunday 23rd Oct 2011 4.19m @ 3:30 AM
8.26m @ 9:52 AM
3.69m @ 4:40 PM
8.89m @ 10:58 PM
Monday 24th Oct 2011 3.32m @ 5:33 AM
9.24m @ 11:39 AM
2.97m @ 6:03 PM
2.4. Video analysis
Geo Oceans customised Visual Basic software program ‘GO Video’ was used for
video analysis that allowed the analyst to assign habitat attributes to the GPS
location (position) where the video was recorded. A marine scientist trained in video
analysis and habitat classification analysed the video footage in real-time (as the
video is recorded). Position data were received at approximately 1-second intervals,
and recorded in a database table, along with the biota and substrate attributes
assigned using the GO Video software. These attributes include visually-assessed
percentage cover estimates of the biota and substrate classes provided in Appendix
1 and Appendix 2. Table 3 lists the attributes that were captured and geo-referenced
using the video analysis software. Figure 1 shows the biota and substrate
classification hierarchy used to group the attributes.
The level of taxonomic detail recorded varied according to the video quality, which
in turn was dependent on the environmental conditions (e.g. water visibility and sea
state) and the speed at which the towed video was filmed. In all cases the video
quality was adequate to make distinctions of the biota into the level 2 groups in
Figure 1.
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