Seabed Habitat Mapping of the Continental Shelf of NSW
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Seabed habitat mapping of the continental shelf of NSW This report was compiled by Alan Jordan, Peter Davies, Tim Ingleton, Edwina Foulsham, Joe Neilson and Tim Pritchard of the Waters and Coastal Science Section, Scientific Services Division, Department of Environment, Climate Change and Water. Published by: Department of Environment, Climate Change and Water NSW 59–61 Goulburn Street PO Box A290 Sydney South 1232 Report pollution and environmental incidents Environment Line: 131 555 (NSW only) or [email protected] See also www.environment.nsw.gov.au Phone: (02) 9995 5000 (switchboard) Phone: 131 555 (environment information and publications requests) Phone: 1300 361 967 (national parks, climate change and energy efficiency information and publications requests) Fax: (02) 9995 5999 TTY: (02) 9211 4723 Email: [email protected] Website: www.environment.nsw.gov.au © Copyright State of NSW and the Department of Environment, Climate Change and Water NSW (DECCW). With the exception of photographs, DECCW and the State of NSW are pleased to allow this material to be reproduced in whole or in part for educational and non-commercial use, provided the meaning is unchanged and its source, publisher and authorship are acknowledged. Specific permission is required for the reproduction of photographs. DECCW has compiled ‘Seabed habitat mapping of the continental shelf of NSW’ in good faith, exercising all due care and attention. No representation is made about the accuracy, completeness or suitability of the information in this publication for any particular purpose. DECCW shall not be liable for any damage which may occur to any person or organisation taking action or not on the basis of this publication. Readers should seek appropriate advice when applying the information to their specific needs. This component of the NSW Seabed Habitat Mapping Project was undertaken by DECCW, with funding provided by State and Commonwealth governments. The project was overseen by the NSW Seabed Habitat Mapping Project Steering committee, consisting of members of DECCW, coastal catchment management authorities, the NSW Department of Industry and Investment (DII), the Commonwealth Department of Environment, Water, Heritage and the Arts and the University of Newcastle. Data was sourced primarily from the Australian Hydrographic Office, Manly Hydraulics Laboratory, Geoscience Australia, NSW Marine Parks Authority, DII, the University of Newcastle and the University of Colorado. All of these contributions were important for the successful completion of the project. Thanks also to Richard Gardner, Michelle Frolich, Aaron Wright and Martin Krogh for their contribution to the project, Brian Hughes for his enthusiasm in co- ordinating the overall project and communicating the results of the work, and Klaus Koop for his ongoing support of the DECCW seabed mapping program. ISBN 978 1 74293 085 5 DECCW 2010/1057 December 2010 Contents Summary……………………………………………………………………………………………..... 1 1. Introduction……………………………………………………………………………………….... 3 2. Objectives…………………………………………………………………………………………… 6 3. Methods……………………………………………………………………………………………... 7 3.1 Nearshore rocky reef and sand…………………………………………………………… 7 3.2 Broadscale rocky reef………………………………………………………………………. 7 3.3 Broadscale bathymetry…………………………………………………………………….. 7 3.4 Broadscale sediments……………………………………………………………………… 10 3.5 Historical seabed maps from central NSW region………………………………………. 10 3.6. Field surveys……………………………………………………………………………….. 10 3.6.1 Sidescan sonar………………………………………………………………………. 10 3.6.2 Acoustic surveys…………………………………………………………………….. 13 3.6.3 Underwater video surveys………………………………………………………….. 16 3.7 Field data processing and analysis……………………………………………………….. 17 3.7.1 Swath acoustic data………………………………………………………………… 17 3.7.2 Underwater video data……………………………………………………………… 19 3.7.3 Assessment of interpretation accuracy…………………………………………… 22 4. Results………………………………………………………………………………………………. 23 4.1 Broadscale bathymetry…………………………………………………………………….. 23 4.2 Broadscale surficial sediments……………………………………………………………. 24 4.3 Seabed habitat extent and structure……………………………………………………… 30 4.3.1 Tweed Heads to Lennox Head…………………………………………………….. 30 4.3.2 Lennox Head to Yamba…………………………………………………………….. 30 4.3.3 Yamba to Woolgoolga………………………………………………………………. 33 4.3.4 Woolgoolga to Scotts Head………………………………………………………… 46 4.3.5 Scotts Head to Tacking Point………………………………………………………. 71 4.3.6 Tacking Point to Crowdy Head…………………………………………………….. 86 4.3.7 Crowdy Head to Seal Rocks……………………………………………………….. 103 4.3.8 Seal Rocks to Newcastle…………………………………………………………… 116 4.3.9 Newcastle to Broken Bay…………………………………………………………… 132 4.3.10 Broken Bay to Stanwell Park……………………………………………………... 137 4.3.11 Stanwell Park to Crookhaven…………………………………………………..… 137 4.3.12 Crookhaven to Bawley Point……………………………………………………… 140 4.3.13 Bawley Point to Bermagui………………………………………………………… 152 4.3.14 Bermagui to Cape Howe………………………………………………………….. 172 5. Discussion………………………………………………………………………………………….. 180 5.1 North coast region………………………………………………………………………….. 184 5.1.1 Seabed habitats……………………………………………………………………... 184 5.1.2 Benthic communities………………………………………………………………... 187 5.2 Central region……………………………………………………………………………….. 190 5.2.1 Seabed habitats……………………………………………………………………... 190 5.2.2 Benthic communities………………………………………………………………... 192 5.3 Southern region……………………………………………………………………………... 193 5.3.1 Seabed habitats……………………………………………………………………... 193 5.3.1 Benthic communities………………………………………………………………... 195 5.4 Conclusion…………………………………………………………………………………… 196 6. References………………………………………………………………………………………...... 198 7. Appendices………………………………………………………………………………………..... 206 Appendix 1. Physical and habitat classes attributed to classified points………………….. 206 Appendix 2. Error assessment of seabed habitat classes………………………………….. 207 Summary This study details the distribution, extent and structure of seabed habitats on the continental shelf of NSW, with particular focus on habitats within NSW state coastal waters. This involved collating and analysing existing broadscale bathymetric and marine sediment datasets, and seabed habitat data defined from previous single-beam and swath acoustic surveys and aerial photography. This was combined with around 100 square kilometres of new swath acoustic data collected using the NSW Department of Environment Climate Change and Water’s (DECCW’s) interferometric sidescan sonar system, allowing the development of high-resolution maps of the seabed bathymetry and habitats. Data from approximately 120 kilometres of vessel-towed underwater video surveys also allowed field validation of swath acoustic data and a description of the visually dominant sessile biota over large areas of the seabed. Analysis of the broadscale bathymetry revealed significant regional and local variations in the depth-structuring of the continental shelf, reflecting regional changes in the angle of the coastline, the local position of prominent headlands and embayments, the presence of offshore islands, and the presence of reefs on the mid-shelf. In addition, variations in the width of the state coastal- waters boundary (5.6–18.4 kilometres) results in considerable regional variability in depth at the boundary (32–132 metres) and, therefore, variability in the range of seabed habitats within NSW waters. The broadscale sediment data indicates significant variations on the inner-shelf, with the patchy occurrence of finer sediments in areas offshore of Yamba, Wooli, Batemans Bay and offshore of the Newcastle, Sydney and Wollongong regions, as well as the presence of coarser sand on the mid- or outer-shelves. Similar areas of coarse sediment were evident on the inner shelf throughout the Solitary Islands, Port Stephens, Sydney and Wollongong regions. The acoustic mapping involved sending acoustic sidescan sonar beams to the seabed and analysing the reflected signals to measure bathymetry and acoustic backscatter (indicating seabed roughness and hardness). Swath acoustic data was combined with existing mapping layers of nearshore reefs defined from aerial photographs, offshore reefs defined from 1:150,000 Australian hydrographic charts, and seabed habitats digitised from historical sidescan sonar data in the Byron Bay, Sydney and Central Coast regions. These datasets were used to map the distribution and extent of seabed habitats, primarily rocky reef and unconsolidated (soft- sediment) habitats, which were mapped into shallow (0–25 metres depth range), intermediate (25–60 metres) and deep (greater than 60 metres) classes. Approximately 1500 square kilometres of swath acoustic coverage from NSW continental shelf waters has been collated from various sources allowing a significant improvement in the information available on the distribution, extent and structure of seabed habitats throughout the region. In general, the distribution of rocky reef and unconsolidated habitats reflects the regional patterns of geology, geological history, coastal inputs and transport of sediments. The broad distribution of rocky reef habitats reflects the patterns of bedrock geology, which varies in its geomorphic and textural attributes (e.g. hardness, grainsize, jointing, folding) and resistance to weathering. Along most of the NSW coast there are prominent rocky reef outcrops seaward of most headlands, although the present surveys have also identified significant reef systems in areas on the continental shelf that are not continuous to the shore, or are continuous to the shore associated with offshore islands. There are