Effects of changes in Great Barrier Reef Marine Park Zoning plans on the 'Magnetic Shoals', off Townsville (MTSRF Project 4.8.2)

Brief description

A baseline survey of 5 green zoned sites on Magnetic Shoals together with 4 adjacent blue zoned areas of the marine park. Surveys were carried out in July, September, October and November 2006 to assess any seasonal effects on the fish and benthic communities in addition to potential zoning effects. The Shoals are characterised by a mosaic of rich epibenthic filter feeding communities typically surrounded by low relief algae and seagrasses. These communities appear to be founded on loose sediments comprised of sand, rubble and foraminifera.A preliminary assessment of the fish communities enumerated with baited video sets (BRUVS) revealed a diverse assemblage across numerous taxonomic and trophic groups. Fish communities associated with patches of habitat were typically more diverse than those from the open, low relief areas and could be discriminated at the scale of 10s of metres. This result underlined the importance of very accurate deployment of sampling gear, especially in respect of on-going temporal monitoring.The blue sites, nominally representing controls for the no-take green sites, included habitat features not present on Magnetic Shoal. These sites were selected on cross-shelf position/depth (the strongest biological gradient on the GBR) and location. They included artificial habitat (a wreck), calcareous reefal substrate and dense filter feeding communities. Many fish species were common to sites both on Magnetic Shoal and in these blue zones yet the concept of control-treatment contrasts cannot be readily applied in this study. Temporal monitoring should focus on the trajectories of each site as simple metrics of abundance and size may be confounded by the disparity between habitats and fish-habitat associations.Thirty percent of all fishes recorded could be classified as targeted or otherwise taken by fishers. This relatively high percentage offers an excellent foundation for monitoring the impact of fishers who have access to a broad range of well represented species. The objective of this task was to establish a baseline on which to build, via ongoing temporal surveys, an understanding of the responses of biological communities (fish and benthos) to differential zoning of human use on inshore "shoals". Areas closed to fishing (green zones) on Magnetic Shoals were compared with adjacent areas open to fishing (non-green zones). Marine Protected Areas (MPAs) are typically predicted to acquire measurable changes in the size, demographics and species composition of fishes (Russ 2002) and this study was designed to capture such changes which might be effected by the re-zoning. In addition, changes in the structure and complexity of the associated benthic communities are documented. Shoal locations:Green - Rap2, Rap12, Rap13, Rap14, Rap15Blue - Rap4, Rap16, RapMP (Mackerel Patch).This is one component in a series of surveys conducted as part of this MTSRF project, see also separate metadata records on:Southern mid-shelf Shoals (East and West Warregos; Karamea and Barcoo Banks)Reef base shoals (Capricorn-Bunker, Pompey and Swains Groups) Shoals off Cardwell Shoals off Cairns.Note that the 'Northern Shoals' of Cardwell, Cairns, and Magnetic Shoals have individual records as each region was analysed separately.

Lineage

Maintenance and Update Frequency: asNeeded

Statement: Statement: Baited Remote Underwater Video Stations (BRUVS) The consisted of a galvanized roll-bar frame enclosing a simple camera housing made from PVC pipe with acrylic front and rear ports. Bait arms (20 mm plastic conduit) and 6 kg galvanised ballast weights were attached and detached during and after deployment. The 1.5m bait arm held a 350 mm plastic mesh bait canister containing one kilogram of crushed pilchards, Sardinops neopilchardus. BRUVS were deployed with 8mm, polyethylene, floating pot ropes and two 30cm surface floats bearing a flag, and were retrieved with a pot hauler.SonyTM MiniDV Handicams (model TRV19) with wide-angle lenses (0.5X adapters)were used in the housings. Exposure was set to 'Auto', focus was set to 'Infinity/manual', MiniDV tapes (Panasonic AY-DVM83PQ) were loaded, SP recording mode used and time codes were laid on the tapes. The BRUVS were deployed to provide 83 minutes of film and were set equidistantly apart (1km-2km) along depth contours to provide independence of each replicate unit.Further information is available in:Cappo M, Harvey E, Malcolm H and Speare P (2003) Potential of video techniques to monitor diversity, abundance and size of fish in studies of Marine Protected Areas. In: Beumer JP, Grant A and Smith DC (eds) Aquatic Protected Areas - what works best and how do we know?, World Congress on Aquatic Protected Areas proceedings, Cairns, Australia, August 2002. p 455-464.Cappo M, Speare P and De'ath 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.All the BRUVS sets deeper than 80m provided very gloomy, grainy footage that could be interrogated only by adjusting the brightness and colour balance of the screen on the tape player. At this time of year, and in these coastal waters, these depths are at the lower limit of penetration of daylight. Beyond them artificial lighting must be employed to obtain useful footage