Surveys of the ecological use of epibenthic habitat by fish in the central Great Barrier Reef using baited remote underwater video stations (BRUVS (TM)) (FRDC Project No. 97/205)

Brief description

BRUVS (TM) were deployed at spatial coordinates known, from previous major studies using fish traps, to be "hot-spots" for the families Lutjanidae (sea perches), Lethrinidae (sweetlip emperors) and Serranidae (coral trout and cod).BRUVS (TM) were deployed at depths between 30 and 70 m in three mid-shelf locations (Davies Reef (9), Kelso Shoals (18), Rib Reef (9)) and in both shallow and deep inshore locations (Calliope Channel (14), Curacoa Channel (27), and Robbery Shoals (3)).Replicate BRUVS (TM), were deployed in daylight hours and the time, depth, latitude and longitude was recorded for each set.Interrogation of each tape provided:- a classification of the habitat at each set, based on estimated sediment composition and/or the nature of epibenthos- the time the BRUVS (TM) settle on the seabed (TOB)- the time of first sighting of a taxa (TFS)- a coarse classification of 'Adult' or 'Juvenile' for these taxa based on size and shape- the time of first feeding of taxa (TFF) in the field of view,- the maximum number of each taxa seen together, or readily identifiable, in any one time on the whole tape (MaxN),- the time at which this maxima occurred (TMaxN)- the behaviour of each taxa toward the bait (passing, scavenging, or feeding), and- the time at which all bait was exhausted if such an event occurred.The habitat categories recognised were: megabenthos, Sargassum, Halimeda, low algae, mud, fine sand, coarse sand, rubble, and 'near benthos'. The 'near benthos' category covered sets where video units landed on sand, but in the far field of view, or during the deployment or retrieval, significant patches of rock or megabenthos were seen.Image grabs also allowed size estimates of fish directly above the scale grid on the bait canister. Baited remote underwater video station (BRUVS (TM)) surveys were undertaken to investigate the relationship between fish requirements for food and shelter and the distribution of sponge, gorgonian and algal 'megabenthos'.The specific questions addressed were:1. what is the nature of fish communities inside and outside megabenthos patches?2. what benthos and sediments characterise some known 'hotspots' for inter-reef lutjanids?The results of the BRUVS (TM) surveys were compared with concurrent RUVS (unbaited) surveys, trapping and underwater visual census (UVC) as methods to census demersal fish. This research was a component of subproject 8, "The ecological usage of epibenthic habitat by key commercial finfish species", of the Fisheries Research and Development Corporation Project No. 97/205, "Dynamics of large sessile seabed fauna, important for structural fisheries habitat and biodiversity of marine ecosystems - and use of these habitats by key finfish species"

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The BRUVS (TM) had clear, acrylic dome ports housing Sony Hi-8 Handycams (model TR516E) with wide-angle lenses (Hama 0.5). The Hama wide-angle lens had a factor of 0.5, reducing the set focal length by 50%. Each housing (made from 12mm UPVC 'blue brute' sewer pipe) was clamped into a galvanised 'roll-bar' frame with lugs for ballasting and lifting, and a pipe mount for pinning bait arms. Bait arms were 1500 mm long electrical conduit of 20 mm diameter. The flexible conduit sustained vigorous attacks by predators on the bait bag and broke away at the pin-holes when snagging occurred during retrieval or when sharks attacked. A 300 mm × 200 mm plastic mesh bait bag was sewn along the arm immediately between 2 'scale grids' of 50 mm × 52 mm. This alignment was intended to allow measurement of fish feeding on the bait bag between the scale grids. The bait consisted of 750 grams of crushed pilchard which was set in the middle field of view and produced a visible oily plume around the station.Exposure was set to 'Auto', focus was set to infinity/manual, short-play (90 minutes) or longplay mode (180 minutes) was selected, and date/time codes were overlaid on footage.The housings and frames were designed and fabricated by the AIMS mechanical workshops and were pressure tested to the equivalent of 80 m depth (the maximum available at the AIMS testing facility).Each BRUVS (TM) was deployed with a polypropylene rope attached to a marker buoy to aid recovery.