CERF Underwater video and stills from SE Tasmania

Full description

Geoscience Australia carried out marine surveys in south-east Tasmania in 2008 and 2009 (GA0315) to map seabed bathymetry and characterise benthic environments through observation of habitats using underwater towed video. Data was acquired using the Tasmania Aquaculture and Fisheries Institute (TAFI) Research Vessel Challenger. Bathymetric mapping was undertaken in seven survey areas, including: Freycinet Pensinula (83 sq km, east coast and shelf); Tasman Peninsula (117 sq km, east coast and shelf); Port Arthur and adjacent open coast (17 sq km); The Friars (41 sq km, south of Bruny Island); lower Huon River estuary (39 sq km); D Entrecastreaux Channel (7 sq km, at Tinderbox north of Bruny Island), and; Maria Island (3 sq km, western side). Video characterisations of the seabed concentrated on areas of bedrock reef and adjacent seabed in all mapped areas, except for D Entrecastreaux Channel and Maria Island. The GA0315_SETasi folder contains video footage; the excel file is the video characterisation data. Underwater video footage represents raw data. Video characterisation dataset include percent cover of substate. This dataset is a contribution to the CERF Marine Biodiversity Hub.

Lineage

Progress Code: completed

Maintenance and Update Frequency: notPlanned

Statement: A total of 55 video transects were surveyed from five study areas (Tasman Peninsula, Freycinet Peninsula, The Friars, Huon river, and Port Arthur channel) in water depths ranging from 15-110 m using Geoscience Australias shallow-water Raytech towed-video system. The towed-camera system housed a forward-facing video camera and associated lights, and was deployed from the stern of the RV Challenger and towed at 0.5 to 1.5 knots. A small electro-hydraulic winch was used to maintain the video system at an altitude of 0.5 - 2 m above the seabed, while a coaxial cable transmitted video footage to the ships video monitor where it was characterised in real-time by the observer and similtaneously recorded to mini DV tapes, which were later copied to digital format. To characterise along-shore and off-shore habitat transitions in each survey area, primary transects were allocated perpendicular to the shoreline and secondary transects (e.g. Fortescue region) were run parallel to shore, intersecting primary transects. Primary transects traversed the greatest depth gradient, and were initiated as close to shore or islands as was safely navigable (approximate 20-30 m water depth on the RV Challenger), and extended out beyond the deepest reefs to characterise both the reef-sediment interface and the adjacent shelf habitat. In areas of deep reefs, transects were run across and beyond each reef (e.g. Roxys Reef). Seabed habitats and biota were characterised in real-time using C-BED (Characterisation of the Benthos and Ecological Diversity) the 3-tiered characterisation scheme of Anderson et al. (2008) that records substratum composition, bedform-relief, and presence of macro- biota. C-BED characterisations were recorded in real-time at 30 second intervals along each transect, or more frequently across transition zones. At each 30-second location, the seabed was evaluated for a period of 15-seconds (i.e. 5 seconds prior to and 10 seconds following the GPS fix) to characterise the seabed. Substrata composition (i.e. rock, boulders (greater than 25.5cm), cobbles (6.5-25.5 cm), gravel, sand and mud) was categorised by primary (greater than 50% cover) and secondary (greater than 20% cover) percent-cover following the protocol of Stein et al. (1992) and Yoklavich et al. (2000). For example, if the seabed was comprised of greater than 50% mud and greater than 20% rock the substratum composition was classified as mud-rock; alternatively greater than 70% mud was classified as mud-mud. This enabled substrata to be subsequently coded as 0%, 20%, 50%, or 70% cover (Anderson and Yoklavich, 2007). Bedform-relief was defined as either softsediment bedform such as hummocky, sediment ripples, or sediment waves, or by the vertical relief of consolidated sediments: relief classes ranged from flat (0 m), low (less than 1 m), moderate (1-3 m), to high relief (greater than 3 m), or rock walls (high-relief with greater than 80 degree incline) (for more detail see Anderson et al., 2007). C-BED characterisations were entered into GNav Real-time GIS Tracker software (Gerry Hatcher, 2002) using a 142 key Cherry programmable keyboard ( Cherry, 2008), which took between 3-12 seconds, and required a two-person team (i.e. observer and data-enterer). A USBL acoustic tracking system was used to track the position of towed-video system to enable CBED characterisations to be accurately correlated with physical features identified in the multibeam bathymetry. For further information on this survey please refer to the post-survey report (GA Record 2009/043: Geocat #69755). Raw data files were parsed and checked for systematic data errors using a SAS macro-program (Statistic Analysis System, SAS Institute Inc., 2001) written by