Assessment of the impact of a cooling water outfall on fish communities in southern Melville Bay, Northern Territory, using Baited Remote Underwater Video Stations (BRUVS (TM))

Brief description

Baited Remote Underwater Video Stations (BRUVS (TM)) were used to non-destructively sample fish within and outside southern Melville Bay towards the end of the dry season (2-6 November, 2007), in light to moderate weather conditions and on the neap tides following the full moon. Sites were selected to enable sampling of the various habitats in Melville Bay, which were identified prior to BRUVS (TM) deployment, from a geo-referenced classification of habitats visualised with a towed camera. Habitats included: mud and silty sediments adjacent the cooling water discharge site at the head of Gove Harbour; nearby and relatively distant seagrass and macroalgal beds; and fringing coral habitats within and outside Southern Melville Bay. The fish communities on the northern side of Gove Peninsula were also examined to provide data to cover the potential for redirection of the cooling water discharge point.BRUVS (TM) sets were deployed in Gove Harbour, Wanaka Bay, Inverell Bay, Half Tide Bay and Middle Bay (30), NoName Bay (6), Northern Beach, Wallaby Rocks and Wallaby Beach (21). BRUVS (TM) were deployed for 1 hour, which was the recording length of the tape. Of the 57 BRUVS (TM) deployed, 22 tapes were assigned as unreadable (39%) due to poor water clarity.In Gove Harbour, 5 sets were placed in the vicinity of the cooling water outfall at the head of the harbour, 4 to the SE around Harbour Islet and 3 approximately 1 km south of the outfall. The 5 sets in vicinity of the outfall and one adjacent to Harbour Islet were over the hydrotalcite rich nepheloid layer of fine gelatinous sediments (the impact zone from the outfall). The remainder (6 sets) were over mud or sandy mud (silt) similarly devoid of benthic structure but included areas with burrowing organisms.Sampling positions, depth, time and associated operational data were secured at the time of deployment. The parameters recorded during the tape reading process were:- classification of the habitat (a still image is grabbed for each set)- identification to species level of all vertebrates observed (following the CAABCodes Australian standard naming convention)- the relative abundance of each species (recorded as 'maxN' - the maximum number visible at one time at any point on the tape)- the 'time of arrival' (Tarr) of each fish species- the life stage of each species (adult or juvenile)- the time elapsed before maxN (TmaxN) and feeding (Tf) was observed for each species The aim of this study was to support the establishment of a monitoring program to address potential impacts of the cooling water discharge of the Alcan Gove refinery on the fish communities of Melville Bay. The towed camera sampling and mapping of habitats are described in a separate metadata record:"Surveys of the marine habitats of southern Melville Bay, Northern Territory, using towed video and aerial photography".

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: BRUVS (TM):Baited Remote Underwater Video Stations (BRUVS (TM)) consist of a galvanized steel trestle shaped frame that is designed to support a video camera clear of visual obstructions on the seafloor and protect the camera and housing from damage in hard and rugged terrain. The camera housing is made from PVC pipe with an acrylic front port with the same optical qualities of seawater thus avoiding any image distortion. A Sony (TM) Mini-DV HandiCam, with wide-angle lens adapter fitted to expand the field of view is mounted in the underwater housing.The fish are attracted to the field of view of the camera by attaching a plastic mesh bait bag containing approximately one kilogram of crushed oily sardines (Sardinops or Sardinella spp) to a pole. This bait bag is positioned 0.6 m from the camera and visible in the centre bottom of the field of view. While it might be supposed that the fish bait would limit the suite of visitors to carnivorous/piscivorous species, the initial feeding activity surrounding the bait invariably attracts members of other trophic groups to the BRUVS (TM). Also, the number of species counted in the presence of the bait bag is invariably greater than that recorded when no bait bag is deployed with the unit.The frame and camera arrangement is tethered to surface floats with 8 mm polypropylene rope to facilitate recovery. One of the floats has a marker flag to increase the daylight visibility of the mooring line for other vessels that might be operating in the vicinity. BRUVS (TM) were deployed for 1 hour, the recording length of the tape, which has proven to be an adequate sampling period for characterising the fish assemblage from a diverse range of habitats from open sandy bottoms to complex coral reefs. BRUVS (TM) were recovered by grappling the surface line between the 2 floats and bringing the rope aboard to a capstan winch.Cappo M, Speare P, De'ath G (2004) Comparison of Baited Remote Underwater Video Stations (BRUVS) and prawn (shrimp) trawls for assessments of fish biodiversity in interreefal areas of the Great Barrier Reef Marine Park. J Exp Mar Biol Ecol 302(2): 123-152.Cappo M, De'ath G, Speare P (2007) Shelf-scale patterns in communities of aquatic vertebrates in the inter-reefal waters of the Great Barrier Reef Marine Park determined by Baited Remote Underwater Video Stations. Mar. Ecol. Prog. Ser. 350: 209-221.Watson D, Harvey E, Anderson M, Kendrick G (2005) A comparison of temperate reef fish assemblages recorded by three underwater stereo-video techniques. Marine Biology 148: 415-425.