Reference point management and the role of catch-per-unit effort in prawn and scallop fisheries Michael F. O’Neill, Anthony J. Courtney, Norm M. Good, Clive T. Turnbull, Kate M. Yeomans, Jonathan Staunton-Smith and Celeste Shootingstar Project No. 1999/120 QO 05001 ISSN 0727-6281 Reference point management and the role of catch-per-unit effort in prawn and scallop fisheries Michael F. O’Neill, Anthony J. Courtney, Norm M. Good, Clive T. Turnbull, Kate M. Yeomans, Jonathan Staunton-Smith and Celeste Shootingstar © The State of Queensland, Department of Primary Industries and Fisheries; Fisheries Research and Development Corporation, 2005 Copyright protects this publication. The State of Queensland has no objection to this material being reproduced but asserts its right to be recognised as author of its original material and the right to have its material remain unaltered. 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Inquiries should be addressed to: Manager, DPI&F Publications Department of Primary Industries GPO Box 46 Brisbane Qld 4001 Table of Contents 1 NON-TECHNICAL SUMMARY.......................................................................1 2 BACKGROUND ..................................................................................................4 3 NEED ....................................................................................................................6 4 OBJECTIVES ......................................................................................................7 5 OBJECTIVE 1. PRODUCE AN IN-DEPTH DESCRIPTION OF THE GEAR AND TECHNOLOGICAL IMPROVEMENTS OF A REPRESENTATIVE SAMPLE FOR THE A) TORRES STRAIT TIGER PRAWN, B) QUEENSLAND EASTERN KING PRAWN AND C) SOUTH- EAST QUEENSLAND SAUCER SCALLOP FISHERIES FOR THE PERIOD 1970 TO PRESENT. ....................................................................................................8 5.1 ABSTRACT ......................................................................................................8 5.2 INTRODUCTION ...............................................................................................9 5.3 MATERIALS AND METHODS ...........................................................................10 5.4 RESULTS .......................................................................................................12 5.4.1 Trends in skippering vessels ................................................................12 5.4.2 Changes in general vessel characteristics...........................................12 5.4.3 Try gear................................................................................................16 5.4.4 Changes in trawl gear..........................................................................17 5.4.5 Uptake of turtle excluder devices and bycatch reduction devices .......25 5.4.6 Changes in navigational technology....................................................25 5.4.7 Changes in communication technology ...............................................26 5.5 DISCUSSION ..................................................................................................29 5.5.1 General vessel characteristics .............................................................29 5.5.2 Changes in nets, ground chains and otter boards ...............................30 5.5.3 Uptake of TEDs and BRDs ..................................................................30 5.5.4 Navigational improvements .................................................................31 5.5.5 Changes in communication..................................................................31 5.6 REFERENCES .................................................................................................32 6 OBJECTIVE 2. ESTABLISH A STANDARDISED CATCH-PER-UNIT EFFORT SERIES: COMPARISON OF RELATIVE FISHING POWER BETWEEN DIFFERENT SECTORS OF THE QUEENSLAND TRAWL FISHERY, AUSTRALIA ..........................................................................................33 6.1 ABSTRACT ....................................................................................................33 6.2 INTRODUCTION .............................................................................................33 6.3 MATERIALS AND METHODS ...........................................................................36 iii 6.3.1 Catch Data...........................................................................................36 6.3.2 Fishing gear and technology data .......................................................36 6.3.3 Statistical analysis ...............................................................................37 6.3.4 Estimating relative fishing power ........................................................38 6.4 RESULTS .......................................................................................................39 6.4.1 Summary of fishing gears and technologies ........................................39 6.4.2 Analysis of prawn and scallop catches ................................................41 6.4.3 Estimates of Fishing Power .................................................................46 6.5 DISCUSSION ..................................................................................................49 6.5.1 Fishing power ......................................................................................49 6.5.2 Stock assessment ..................................................................................51 6.5.3 Statistical comments.............................................................................51 6.5.4 Conclusion ...........................................................................................52 6.6 FURTHER DEVELOPMENT..............................................................................52 6.7 ACKNOWLEDGMENTS....................................................................................52 6.8 REFERENCES .................................................................................................53 7 OBJECTIVE 3. COMPARE PRESENT MANAGEMENT PLAN REFERENCE POINTS WITH THE ADJUSTED AND UNADJUSTED CATCH-PER-UNIT EFFORT SERIES..................................................................55 7.1 ABSTRACT ....................................................................................................55 7.2 INTRODUCTION .............................................................................................55 7.2.1 Current Queensland reference points..................................................56 7.3 METHODS......................................................................................................57 7.3.2 Chart interpretation.............................................................................58 7.4 RESULTS .......................................................................................................59 7.4.1 Review charts based on average over all months within period. ........59 7.4.2 Review period charts based on each month within a period. ..............67 7.5 DISCUSSSION.................................................................................................76 7.6 REFERENCES .................................................................................................76 8 OBJECTIVE 4. INVESTIGATE AND ESTABLISH ROBUST REFERENCE POINTS AND RESPONSE MECHANISMS THROUGH SIMULATION ...........................................................................................................77 8.1 ABSTRACT ....................................................................................................77 iv 8.2 INTRODUCTION .............................................................................................77 8.3 METHODS......................................................................................................81 8.3.1 Catch and Effort Data..........................................................................81 8.3.2 Standardisation of Catch Rates ...........................................................83 8.3.3 Delay Difference Modelling.................................................................85 8.3.4 Age Structured Modelling....................................................................88 8.3.5 Surplus Production Modelling.............................................................91 8.3.6 Statistical Uncertainty in Models.........................................................92 8.3.7 Historical Trawl Data..........................................................................94 8.3.8 Spawner-recruitment Relationships.....................................................97 8.3.9 Equilibrium Reference Points..............................................................99 8.3.10