Assessment of the Snapper Fishery in Victoria Final Report Project No. 97
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Assessment of the snapper fishery in Victoria Patrick C. Coutin, Shellie Cashmore and K.P. Sivakumuran Final Report Project No. 97/128 Assessment of the snapper fishery in Victoria Patrick C. Coutin, Shellie Cashmore and K.P. Sivakumuran Project No. 97/127 Fisheries Research and Development Corporation Assessment of the snapper fishery in Victoria Patrick C. Coutin, Shellie Cashmore and K.P. Sivakumuran Marine and Freshwater Resources Institute PO Box 114, Queenscliff, Victoria, 3225 June 2003 © The State of Victoria, Department of Primary Industries, 2003 ISBN: 1 74106 185 7 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. FRDC 97/127 Snapper Assessment in Victoria Final Report TABLE OF CONTENTS LIST OF TABLES ..................................................................................................... III LIST OF FIGURES .................................................................................................... V ABBREVIATIONS .................................................................................................. VIII NON–TECHNICAL SUMMARY .............................................................................. 1 OUTCOMES ACHIEVED .......................................................................................... 1 SUMMARY .................................................................................................................. 2 BACKGROUND .......................................................................................................... 5 NEED ............................................................................................................................ 6 PROJECT OBJECTIVES ........................................................................................... 7 METHODS ................................................................................................................... 7 Objective 1. Development of models to assess the snapper stocks .......................... 7 Modelling of fisheries data .......................................................................................... 7 Biological models .......................................................................................................... 8 The integrated movement, growth and fisheries model ......................................... 10 Objective 2. Tagging strategies and experimental design ...................................... 12 Development of a snapper tagging database ........................................................... 16 Tag retention experiments ........................................................................................ 17 Objective 3. Environment–recruitment models ...................................................... 18 Objective 4. Spawning season and location ............................................................. 22 Sampling of gut contents ........................................................................................... 25 RESULTS ................................................................................................................... 26 Commercial fisheries data analyses ......................................................................... 26 Analyses and modelling of biological data ............................................................... 31 Development of an integrated movement, growth and fisheries model ................ 42 Recaptures of tagged snapper by tag type and release location ............................ 43 Marine and Freshwater Resources Institute i FRDC 97/127 Snapper Assessment in Victoria Final Report Dispersal of the western snapper stock by location of release ............................... 51 Dispersal of the eastern snapper stock by location of release ................................ 61 Tag retention experiments ........................................................................................ 63 Tag retention models ................................................................................................. 65 Environment and recruitment relationships ........................................................... 68 Spawning season and location ................................................................................... 88 The diet of snapper in Port Phillip Bay and coastal waters ................................... 91 DISCUSSION ............................................................................................................. 99 Snapper stock abundance .......................................................................................... 99 Integrating snapper movement, growth and in fisheries assessment .................. 100 Snapper tagging and movement studies ................................................................ 101 Comparison of snapper dispersal behaviour ......................................................... 102 Performance of different types of tags ................................................................... 104 Environment-recruitment models .......................................................................... 104 Reproductive biology ............................................................................................... 108 Snapper diet .............................................................................................................. 112 Fishery Management Implications ......................................................................... 115 PLANNED OUTCOMES ........................................................................................ 116 BENEFITS ................................................................................................................ 117 FURTHER DEVELOPMENTS ............................................................................. 117 CONCLUSION ........................................................................................................ 118 REFERENCES ......................................................................................................... 119 ACKNOWLEDGMENTS ....................................................................................... 130 APPENDIX 1: INTELLECTUAL PROPERTY ................................................... 132 APPENDIX 2: STAFF ............................................................................................. 133 APPENDIX 3: EXTENSION .................................................................................. 134 APPENDIX 4: SNAPPER TAG RELEASE AND RECAPTURE DATA .......... 136 APPENDIX 5: LATITUDE AND LONGITUDE OF RECAPTURES ............... 201 Marine and Freshwater Resources Institute ii FRDC 97/127 Snapper Assessment in Victoria Final Report List of Tables Page Table 1. Macroscopic maturation stages of snapper gonads ........................................ 23 Table 2. Histological description of the oocytes of female snapper ............................ 24 Table 3. Standardised CPUE models for the commercial snapper fishery in Port Phillip Bay. .................................................................................................. 27 Table 4. Standardised CPUE models for the commercial snapper fishery in the west coast of Victoria ........................................................................................... 27 Table 5. Standardised CPUE models for the commercial snapper fishery in the east coast of Victoria ........................................................................................... 31 Table 6. Length weight relationships for snapper. ...................................................... 31 Table 7. Mean fork length at age estimated from sectioned otoliths of snapper sampled in Port Phillip Bay. ........................................................................ 35 Table 8. Mean fork length at age estimated from sectioned otoliths of snapper in eastern Victoria ............................................................................................ 36 Table 9. Mean fork length at age estimated from sectioned otoliths of snapper in western Victoria ........................................................................................... 37 Table 10. A summary of tagged snapper released in 1948-1994 and recaptured ........ 47 Table 11. A summary of tagged snapper released in 1995-2003 and recaptured ........ 47 Table 12. Tag retention models for internal, dart and Tbar tags derived from linear regressions. .................................................................................................. 67 Table 13. Relationships between environmental variables in the 0+ year and year class strength of 1+ snapper based on trawl surveys between 1989 – 1999. ....... 81 Table 14. Relationships between environmental variables and year class strength from the abundance of +3 to +18 old snapper in catches between 1994-1998. 81 Table 15. Size frequency distribution of oocytes in different stages of development from oocyte diameter measurements. ......................................................... 90 Table 16. The percentage of empty stomachs observed in each zone by season and length class .................................................................................................. 91 Table 17. Changes in diet of snapper (n= 115) caught