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Deeper water fish and benthic surveys
in the Lord Howe Island Marine Park:
February 2004
Methods
Towed video
A half inch 3CCD colour video camera mounted on a vane and controlled by
a winch with 320m of electromechanical cable provided the visual imagery
of the benthos to a shipboard miniDV tape recorder. Two 12Volt, 35Watt
underwater lights illuminated the field of view. The tape recorder also
received GPS data (position, ground speed, true heading, date and time),
which was written to the audio track for later retrieval. A
computer-based application allowing keyboard classification of
substrata, benthos and individual organisms (Table 1) was interfaced
with a GPS to facilitate real-time geo-referencing of all data points.
C-Maptm vector
charts and Maxseatm
electronic navigation software were used to record the ship’s track and
depth. Data points were recorded at 8-second intervals (or immediately a
new class or organism was sighted). With an average speed over the
ground of 1.5 knots, a resolution of 6m was achieved. A 5 megapixel
still camera with external strobe was mounted to the tow body and set to
record a still image at 1 minute intervals. This gear was deployed at 21
stations around Lord Howe and Balls Pyramid (Figure. 2 and Table 2).
Because of the rough conditions, much of the boat movement was
translated to the towed camera making it difficult to maintain altitude
above the bottom. This was especially difficult on the steeper slopes,
and the decreasing natural light caused the auto iris to continually
hunt for depth of field/focus. As a consequence, the towed camera
provided coarser resolution of the benthos than might otherwise have
been achieved in fine weather conditions.
 Figure 2. Chart of the study
area showing the location of video tows and BRUVS sets.
Table 1. Substrata and benthic categories
employed on the towed video to classify the habitats and individual
organisms recognised.
|
Substrates |
Benthos |
Organisms |
|
|
Alcyonarians, Dense |
Solitary Coral |
|
Silt (Sandy-Mud) |
Alcyonarians, Medium |
Bryozoan |
|
Sand |
Alcyonarians, Sparse |
Hydroid |
|
Coarse Sand |
Gorgonian Garden, Dense |
Crinoid |
|
Sand Waves / Dunes |
Gorgonian Garden, Medium |
Urchin |
|
Rubble (5-50mm) |
Gorgonian Garden, Sparse |
Starfish |
|
Stones (50-250mm) |
Whip Garden, Dense |
Crab |
|
Rocks (> 250mm) |
Whip Garden, Medium |
Holothurian |
|
Bedrock / Reef |
Whip Garden, Sparse |
Gastropod |
|
|
Hard Coral Garden (Flowerpots), Dense |
Ascidian |
|
|
Hard Coral Garden (Flowerpots), Medium |
Anemone |
|
|
Hard Coral Garden (Flowerpots), Sparse |
Sea Pen |
|
|
Live Reef Corals |
|
|
|
Porifera (Sponge) Garden, Dense |
|
|
|
Porifera (Sponge) Garden, Medium |
|
|
|
Porifera (Sponge) Garden, Sparse |
|
|
|
Algae |
|
|
|
Kelp |
|
|
|
Seagrass |
|
|
|
Bivalve Shell Beds |
|
|
|
Burrowing Animals (Bioturbated Mud) |
|
|
|
No Benthos |
|
Table 2. Location of underwater video tows and the depths
surveyed. More comprehensive information on each tow is given in
Appendix 1.
|
Tow |
Rise |
Location |
Depth range (m) |
|
LHI01 |
Lord Howe |
NE shelf |
|
|
LHI02 |
Lord Howe |
NE shelf |
|
|
LHI03 |
Lord Howe |
NE shelf |
32 - 58 |
|
LHI04 |
Lord Howe |
N slope |
58 - 86 |
|
LHI05 |
Lord Howe |
SW slope |
60 - 220 |
|
LHI06 |
Lord Howe |
SW slope |
|
|
LHI06 |
Lord Howe |
SW slope |
109 - 195 |
|
LHI07 |
Lord Howe |
SW slope |
82 - 210 |
|
LHI08 |
Lord Howe |
SW slope |
58 - 200 |
|
LHI09 |
Lord Howe |
SE shelf |
23 - 44 |
|
LHI10 |
Lord Howe |
SE shelf |
23 - 44 |
|
LHI11 |
Lord Howe |
E shelf |
23 - 43 |
|
LHI12 |
Lord Howe |
E slope |
52 - 200 |
|
LHI13 |
Lord Howe |
SE slope |
58 - 185 |
|
LHI14 |
Balls Pyramid |
N slope |
49 - 150 |
|
LHI15 |
Balls Pyramid |
NE shelf |
67 - 74 |
|
LHI16 |
Balls Pyramid |
NE slope |
46 - 195 |
|
LHI17 |
Balls Pyramid |
S shelf |
27 - 42 |
|
LHI18 |
Balls Pyramid |
E slope |
70 - 156 |
|
LHI19 |
Balls Pyramid |
W shelf |
82 - 90 |
|
LHI20 |
Balls Pyramid |
W slope |
99 - 202 |
|
LHI21 |
Lord Howe |
W shelf |
31 - 108 |
December 18, 2008
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