Surveys of fish-habitat associations using Baited Remote Underwater Video Stations (BRUVS (TM)) offshore from Port Hedland, Western Australia

Brief description

In July 2012, baited remote underwater video stations (BRUVS (TM)) were deployed in the vicinity of Port Hedland, in two areas parallel to the coast (inshore and offshore) on either side of the shipping channel and some dredge spoil grounds, in depths of 4.6 to 24 metres.The survey design specified the deployment of 230 BRUVS (TM) at random within grids of the two study areas, at a spacing not less than 450 metres apart, to minimise the likelihood of individuals moving between stations and being double-counted. Of the 230 BRUVS (TM) deployed during the field campaign, 221 produced imagery of sufficient quality for analysis.Commencing immediately after reaching the seafloor, 60 minutes of bottom-time was analysed for all video recordings, regardless of whether video extended longer. Data was recorded using a purpose built interface and included identification to species level and life stage (adult or juvenile) of all vertebrates, relative abundance (MaxN ; maximum number visible at any single point on the tape), time of arrival and the time elapsed before MaxN and feeding occurs. Depth and GPS position of each deployment, estimates of water clarity and the timing of ancillary events such as feeding activity and loss of bait bag were also recorded.The habitat at each station was classified by reviewing an image of the seafloor from each of the BRUVS (TM) sampling stations. To provide quantitative estimates of habitats, the percentage cover (to the nearest 10%) was then determined for six categories of (abiotic) substratum, summed to 100%, and for 12 categories of (biotic) epibenthos, also summed to 100%. This study was undertaken to provide baseline estimates of fish diversity and relative abundance in direct relation to habitat and depth within inshore and offshore areas in the vicinity of Port Hedland, where a large expansion of port facilities will be accompanied by dredging and relocation of dredge spoil on adjacent seabeds in the local region.

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Maintenance and Update Frequency: notPlanned

Statement: Statement: BRUVS (TM) survey gear:A BRUVS (TM) consists of a galvanised steel frame onto which a camera housing, bait arm, ballast weights, ropes and floats are attached. A Sony MiniDV digital handicam is used to film through an acrylic port within a PVC underwater housing, pressure-rated to depths of 100 m. A flexible bait arm holds a plastic mesh bait bag containing 1 kg of minced pilchards (Sardinops sagax neopilchardus) at a distance of approximately 1 m in front of the camera lens. BRUVS (TM) frames are ballasted according to the prevailing sea-state and current conditions to ensure stability on the seabed. An 8 mm diameter polypropylene rope with surface floats attached enables the BRUVS (TM) to be deployed and later retrieved from the surface. The scope of the rope length was selected to be approximately twice the water depth.Data collection and management:The full high definition video footage (1920 x1080 at 30fps) was downloaded from SD card to portable hard drive and converted to DivX HD format (.avi) for analysis after each deployment. The video footage is stored on portable hard drives in duplicate at AIMS Townsville. Sampling positions and other metadata were checked and uploaded into the AIMS BRUVS5.2.mdb© database at the conclusion of the field work. This database provides an interface with an .avi video player to:- navigate within the imagery- to capture time codes and still images to quantify data- to store and cross-reference images with our existing library of 3000 reference images- to ensure quality control of fish identifications and- to retrieve data for analysis.The data collection interface is well-established and provides for recording of in situ habitat classification, identification to species level and life stage (adult or juvenile) of all vertebrates, relative abundance (MaxN ; maximum number visible at any single point on the tape), time of arrival, the time elapsed before MaxN and feeding occurs, and records the observer identity for quality assurance and control. A full description of data collection and management protocols can be obtained from the senior author (m.cappo@aims.gov.au).Fish identification and counts:Where possible, individuals were identified with their full binomial name, to genus and species. However, where multiple individuals in a known genus could be grouped as a species, but the species name itself was unknown, they were labelled as Genus sp1 to n where n was the total number of unknown but distinctly identifiable taxa in the genus. If a species could be recognised as unique, but not identified to either species or genus, it was labelled as Family sp 1 to n. As such, these latter taxonomic groupings represent unique albeit unknown taxa and were counted as species.Estimates of relative abundance were the maximum number of fish belonging to each species present in the field of view at one small time period (MaxN). This conservative measure avoids repeated counts of the same individual as only a portion of the total number of individuals in the area may be viewed at one time. The use of MaxN as a conservative estimate of relative abundance has been reviewed extensively.Willis TJ, Millar RB, Babcock RC (2000) Detection of spatial variability in relative density of fishes: comparison of visual census, angling, and baited underwater video. Marine Ecology Progress Series 198: 249-260.Cappo M, Speare P, D'eath G (2004) Comparison of Baited Remote Underwater Video Stations (BRUVS) and prawn (shrimp) trawls for assessments of fish biodiversity in inter-reefal areas of the Great Barrier Reef Marine Park. Journal of Experimental Marine Biology and Ecology 302(2): 123-152.Cappo M, Harvey E, Shortis M (2007) Counting and measuring fish with baited video techniques - An overview. Australian Society for Fish Biology 2006 Workshop Proceedings, p. 101-114.Identification of individual fish was aided by the use of high definition video, relevant literature and the AIMS image and video reference libraries. All fish data and still reference images were run through QA/QC procedures prior to being incorporated into the Oracle AIMS BRUVS database via BRUVS5.2.mdb.The use of scientific names followed the codes and conventions of the Commonwealth codes for Australian aquatic biota (CAABCodes):Rees AJJ, Yearsley GK, Gowlett-Holmes K, Pogonoski J Codes for Australian Aquatic Biota (on-line version). CSIRO Marine and Atmospheric Research, World Wide Web electronic publication, 1999 onwards. Available at: http://www.cmar.csiro.au/caab/.The use of common names follows:Allen GR, Swainston R (1988) The marine fishes of north-western Australia. A field guide for anglers and divers. Western Australian Museum, Perth, Western Australia. 201 pp.Classification of the benthos:Each BRUVS (TM) deployment provided a view of the adjacent seabed and thus provides habitat data for that sampling station. For the current study, a standardised classification scheme for the seabed in the BRUVS (TM) field of view was developed and applied by reviewing an image of the seafloor from each of the BRUVS (TM) sampling stations. To provide quantitative estimates of habitats, the percentage cover (to the nearest 10%) was then determined for six categories of (abiotic) substratum, summed to 100%, and for 12 categories of (biotic) epibenthos, also summed to 100%. Each of the '% cover' variables was measured on the same scale, so no data transformations were made. Some of the categories of substratum or epibenthos were absent, or poorly represented in the dataset. Those were pooled with other, larger and related categories to derive the shorter list of covariates.Substratum categories:boulderscalcareous reefbedrockgravelrubblesandmud/siltEpibenthos categories:no epibenthosencrusting organismsfansanemoneshydroidsmacroalgaemassive coralssoft coralssolitary corals (eg. Turbinaria)spongessea whipsseagrass