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.

Notes

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.

Doherty, PJ: AIMS (Principal Investigator)

Speare, PJ: AIMS

Stowar, M: AIMS

Cappo, M: AIMS