Testing the Management Rules for Scallops in Bass Strait
Total Page：16
File Type：pdf, Size：1020Kb
JUVENILE SCALLOP DISCARD RATES AND BED DYNAMICS: TESTING THE MANAGEMENT RULES FOR SCALLOPS IN BASS STRAIT. Malcolm Haddon, Julian J Harrington, Jayson M Semmens July 2006 FRDC Project 2003/017 © Fisheries Research and Development Corporation and Tasmanian Aquaculture and Fisheries Institute 2006 This work is copyright. Except as permitted under the Copyright Act 1968 (Cth), no part of this publication may be reproduced by any process, electronic or otherwise, without the specific written permission of the copyright owners. Neither may information be stored electronically in any form whatsoever without such permission. The Fisheries Research and Development Corporation plans, invests in and manages fisheries research and development throughout Australia. It is a statutory authority within the portfolio of the federal Minister for Agriculture, Fisheries and Forestry, jointly funded by the Australian Government and the fishing industry. Spatial Dynamics of Scallop Beds Table of Contents Juvenile Scallop Discard Rates and Bed Dynamics: Testing the Management Rules for Scallops in Bass Strait. i Non Technical Summary 1 Objectives: 1 Benefits and Adoption: 2 Non-Technical Summary: 3 Acknowledgements 7 Background 7 Need 9 Objectives 9 Structure of the report 10 1. Commercial Scallops (Pecten fumatus) and Spatial Management. 11 1.1 Introduction 11 1.2 Biology and Ecology of Pecten fumatus 12 1.2.1 Distribution 12 1.2.2 Reproduction and Recruitment 12 1.2.3 Post-Settlement Growth 13 1.3 History of the Bass Strait Scallop Fisheries: Boom and Bust 13 1.3.1 Pre 1980 14 1.3.2 The Boom: 1980 - 1986 14 1.3.3 Post 1990 15 1.4. Why the ‘Busts’? 16 1.5. The Introduction of Spatial Management Strategies 17 1.5.1 Victorian Fishery 17 1.5.2 Central Bass Strait (Commonwealth) Fishery 18 1.5.3 Tasmanian Fishery 18 1.5.4 Other Legislation 18 1.5.5 Current Management Strategies 19 1.6 Testing the Management Rules for Scallops (FRDC 2003/017) 19 2. Use of VMS Data to Determine the Extent and Intensity of Scallop Fishing. 20 2.1 Introduction 20 2.2 Use of VMS in Survey Design and Analysis 20 2.2.1 Data ‘Screening’ 21 2.2.2 Defining Fishing Extent and Intensity of Fishing 21 2.2.3 Defining Fishing Extent and Intensity of Fishing 22 2.3 Results 22 Page ii FRDC Final Report, Project 2003/017 Spatial Dynamics of Scallop Beds 2.3.1 Commonwealth-Managed Fishery – Extent and Intensity of Fishing 22 2.3.2 Tasmanian-Managed Fishery – Extent and Intensity of Fishing 26 2.3.3 Comparison of Tasmanian with Commonwealth Scallop Beds 29 2.3.4 Accuracy of VMS Methodology 29 2.4 Potential Improvements of VMS Methodology 32 2.5 General Discussion 33 2.6 General Conclusions 35 3. Dredged Benthic Assemblages. 36 3.1 Introduction 36 3.2 Methods and Materials 36 3.3 Results / Discussion 40 3.3.1 Species List 40 3.3.2 Basic Descriptive Statistics 44 3.3.3 Distribution of the Major Bycatch Species 45 3.4 Conclusions 51 4. ‘Good’ and ‘Marginal’ Scallop Beds. 52 4.1 Introduction 52 4.2 Methods and Materials 52 4.2.1 Between Scallop Bed Comparison 53 4.2.2 Within Scallop Bed Comparisons 53 4.2.3 Statistical Analysis 54 4.3 Results 55 4.3.1 Between Scallop Bed Differences 55 4.3.2 Benthic Communities in Scallop Beds Located in Commonwealth Managed Regions 57 4.3.3 Benthic Communities in Scallop Beds Located in Tasmanian Managed regions 60 4.4 Discussion 61 4.4.1 Benthic Assemblages of Different Scallop Beds 61 4.4.2 ‘Good’ and ‘Marginal’ Scallop Beds 62 4.4.3 Scallop Abundance: Implications for Scallop Fishery Management 62 4.4.4 Conclusions 63 5. The Consequences of Differing Intensities of Scallop Dredge Fishing Upon Benthic Communities. 64 5.1 Introduction 64 5.2 Methods and Materials 65 5.2.1 Survey Design and Methods 65 5.2.2 Statistical Analysis 67 5.3 Results 67 5.3.1 Commonwealth-Managed Fishery 67 FRDC Final Report Project 2003/017 Page iii Spatial Dynamics of Scallop Beds 5.3.2 Tasmanian-Managed Fishery 70 5.4 Discussion 73 5.4.1 Defining Scallop Beds – Discrete vs. Patchy 75 5.4.2 Implications for Management 75 6. Sequence of Surveys: Overview of Survey Results. 76 6.1 Introduction 76 6.2 General Methods 76 6.2.1 Dredge Surveys 77 6.2.2 Modal Groups and Length Frequency 78 6.3 Results 81 6.3.1 Findings from the Sequence of Surveys 81 6.3.2 Recruitment Events: Overview 83 6.4 Discussion 88 6.4.1 Scallops do not Die at 80 mm Shell Length 88 6.4.2 Broader Scale Settlement of Scallops can Occur 88 6.4.3 Commercial Fishing does Not Kill all Scallops 88 7. Variable Growth of Scallops. 89 7.1 Introduction 89 7.2 Methods 91 7.2.1 General Methods 91 7.2.2 Statistical Analyses 92 7.3 Results 93 7.3.1 Top (Right) Valve Weight vs Lower (Left) Valve Weight 94 7.3.2 Height Predicted by Length 96 7.3.3 Shell Depth Predicted by Length 97 7.3.4 Scallop Shell Weight vs Shell Length 98 7.3.5 Meat Weight as Predicted by Shell Length 100 7.4 Discussion 102 7.4.1 Relative Growth and the Discard Rule 102 7.4.2 Shell Fragility 103 8. Scallop Bed Dynamics. 104 8.1 Introduction 104 8.2 General Methods 104 8.2.1 Modal Analysis of Length Frequency Data: Measuring Scallop Growth 105 8.2.2 The Impact of Fishing on Scallops 106 8.3 Results 107 8.3.1 Growth Rates 107 8.3.2 Effect of Scallop Density on Growth 111 Page iv FRDC Final Report, Project 2003/017 Spatial Dynamics of Scallop Beds 8.3.3 Patterns of Scallop Density and Size within a Bed 113 8.3.4 The Impact of Fishing on Scallops 116 8.4 Discussion 118 8.4.1 Ageing vs Modal Progression 118 8.4.2 The Impact of Commercial Fishing on Scallops 119 8.4.3 Juvenile Settlement Success and Fishing Intensity. 120 8.4.4 Management Implications 120 9. Underwater Video Scallop Surveys. 123 9.1 Introduction 123 9.2 The Underwater Video System 123 9.3 Video Observations of Different Habitat Types 125 9.3.1 Dense Scallop Bed 125 9.3.2 Dense Doughboy and Commercial Scallop Habitat 126 9.3.3 Barren Ground 126 9.3.4 Screwshell Habitat 126 9.3.5 Soft Bottom Sponge Habitat 127 9.4 Problems with Underwater Video Scallop Surveys 127 9.4.1 Collection of Video in the Field 127 9.4.2 Post-Survey Analysis of Video 128 9.5 Future Directions in Video Surveys 129 9.5.1 Ability to Measure Scallops 129 9.5.2 Automated Video Analysis 129 10. Acoustic Surveys of Scallop Beds and Examining the Impact of Dredging. 131 10.1 Introduction 131 10.2 Methods 131 10.2.1 Study Site 131 10.2.2 Detection of Known Scallop Habitat 132 10.2.3 Single Beam Acoustic Survey Design 133 10.2.4 Single Beam Acoustic Data Analysis 133 10.2.5 Detecting Scallop Habitat using Single-Beam Acoustics 135 10.2.6 Detecting the Impact of Scallop Dredging using Single-Beam Acoustics 135 10.2.7 Bathymetry 135 10.2.8 Side Scan Sonar 136 10.3 Results 136 10.3.1 Identifying Levels of Fishing Activity 136 10.3.2 Single Beam Acoustics – Detecting Scallop Habitat 137 10.3.3 Single Beam Acoustics – Detecting the Impact of Scallop Dredging 139 10.3.4 Bathymetry 140 10.3.5 Side Scan Sonar 141 FRDC Final Report Project 2003/017 Page v Spatial Dynamics of Scallop Beds 10.4 Discussion 142 10.4.1 Detecting Scallop Habitat using Single Beam Acoustics 142 10.4.2 Is bathymetry the Answer? 143 10.4.3 Detecting the Impact of Dredge Fishing 143 10.5 Conclusions 144 11. Fishery Dependent Surveys. 145 11.1 Introduction 145 11.2 Exploratory Permit Fishing, 2003 145 11.2.1 Expression of Interest and Allocation of Permits 145 11.2.2 Methodologies: Data Entry and Analysis 146 11.2.3 Results: An Overview 146 11.2.4 Usability of Data in Analysis / Presentation 147 11.2.5 Complete Data / Survey Technique 147 11.2.6 Partially Complete Data / Survey Technique 148 11.2.7 Incomplete Data / Survey Technique 150 11.3 Designing Credible, Industry Based Surveys (FRDC 2005/027) 151 12. Scallop Fishery Regulations and Spatial Management. 153 12.1 Introduction 153 12.2 The Main Biological and Ecological Conclusions 153 12.2.1 The Spectrum of ‘Good’ to ‘Marginal’ Beds 153 12.2.2 Growth Rates, Longevity and Management 154 12.2.3 Recruitment Events 155 12.2.4 Fishing Disturbance and Scallops 155 12.3 History of Management Regulations. 155 12.3.1 Offshore Constitutional Settlement (OCS) 155 12.3.2 Limited Entry Fishery / Non-Transferable Licences 158 12.3.3 Quota Units, Total Allowable Catches (TAC) and Trip / Period Quotas 159 12.3.4 Seasonal Closures 161 12.3.5 Legal Minimum Sizes, the 20% Trashing Rate Rule and Two Spawnings Rule 162 12.3.6 Fishery Closures: Insufficient Scallop Stocks 165 12.4 Alternative Spatial Management Regimes. 165 12.4.1 Spatial Management Strategies Revisited 165 12.4.2 Advantages and Disadvantages of Different Spatial Management Approaches 166 12.4.3 Which Strategy is the Best? 168 12.4.4 Other Management Requirements in a Most Closed / Little Open Spatial Management Regime 168 12.5 Spatial Management and a Fishery Each Year.