Deeper water benthic surveys in the Lord Howe Island Marine Park (Commonwealth Waters) using towed video (Towvid)

Full description

In February/March 2004, surveys of benthic habitats and fish faunas were undertaken in deeper waters of the Commonwealth waters surrounding Lord Howe and Balls Pyramid rises. Towed video gear (Towvid) was deployed at 21 stations around Lord Howe Island and Balls Pyramid. Deployments were located on the north east shelf (3), north slope (1), south west slope (5), south east shelf (2), east shelf (1), east slope (1) and south east slope (1) and west shelf (1) of Lord Howe Island. Single deployments were also made on the north slope, north east slope, south shelf, east slope, west shelf and the west slope of Balls Pyramid. A computer-based application, allowing keyboard classification was used to analyse the video tapes. Habitats were classified based on the substrata (9 categories), overlying epibenthos (10 categories) and individual organisms (2 categories) viewed on the tapes.
This preliminary, rapid ecological assessment aimed to describe habitats and fish-habitat associations in deeper waters, below the depth limits of SCUBA observations. Towvid data was used to provide an overall quantitative perspective of the various habitats occurring in these waters.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: A half inch 3CCD colour video camera was 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 12 Volt, 35 Watt 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 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 stills camera with external strobe was mounted to the tow body and set to record a still image at 1 minute intervals. 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.Substrate, overlying epibenthos and individual organism categories employed for towed video to classify the habitats and individual organisms recognised:Substrate (abiotic substrate components):Silt (Sandy-Mud)Sand Coarse SandSand Waves / Dunes Rubble (5-50mm) Stones (50-250mm)Rocks (> 250mm)BedrockBedrock / ReefOverlying Epibenthos:Gorgonian Garden, DenseGorgonian Garden, MediumGorgonian Garden, SparseWhip Garden, DenseWhip Garden, MediumWhip Garden, SparseWhip Garden, Medium/algae/kelpAlgaeKelpNo BenthosIndividual Organisms:Solitary CoralSpongeThe percentage cover of benthic communities was classified as follows:S - sparse (0 - 30% cover)M - medium (30 - 60%)D - dense (>60%)

Notes

Credit
Speare, Peter J, Mr (Co Investigator)