Prawn Fishery By-catch and Discards: marine ecosystem analysis – population effects Ib Svane, Kate Rodda & Philip Thomas 2007 Project No. 2003/023 Prawn Fishery By-catch and Discards: marine ecosystem analysis – population effects Ib Svane, Kate Rodda & Philip Thomas 2007 Project No. 2003/023 SARDI Aquatic Sciences Publication No. RD 03-0132 SARDI Research Report Series No. 199 Principal Investigator Dr Ib Svane South Australian Research and Development Institute Aquatic Sciences Lincoln Marine Science Centre Hindmarsh Street, Port Lincoln SA 5606 Ph: +618 8683 2562 Fax: +618 8683 2520 Email: [email protected] COPYRIGHT © Fisheries Research and Development Corporation and SARDI, 2007. 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. DISCLAIMER Although SARDI has taken all reasonable care in preparing this report, neither SARDI nor its officers accept any liability resulting from the interpretation or use of the information set out in this document. Information contained in this document is subject to change without notice. SARDI Aquatic Sciences Publication No RD 03-0132 SARDI Research Report Series No. 199 ISBN: 0 7308 5361 6 Printed in Adelaide, March 2007 Authors: Ib Svane, Kate Rodda, Philip Thomas Reviewed by: J. Tanner and J. Carragher Approved by: J. Carragher Signed: Date: 21st March 2007 Distribution: PIRSA Fisheries, South Australian Fisheries Research Advisory Boards, WC&SGPFA, SARDI Aquatic Sciences Library, State Library, Parliamentary Library, National Library, SARDI Executive Library. Circulation: Public domain “It’s an accident that our culture invented writing and reading. It’s a cultural artefact we’ve developed, but it’s not in the nature of man. Two hundred years from now, we won’t need this medium to transmit knowledge.” Marcel Just, neuroscientist – the Bulletin, June 2006. TABLE OF CONTENTS COPYRIGHT..........................................................................................................4 DISCALIMER ........................................................................................................4 NON TECHNICAL SUMMARY ...............................................................................1 OBJECTIVES ................................................................................................................1 KEYWORDS .................................................................................................................4 ACKNOWLEDGEMENTS................................................................................................4 CHAPTER 1: GENERAL INTRODUCTION..........................................................5 BACKGROUND.............................................................................................................6 NEED...........................................................................................................................7 OBJECTIVES ................................................................................................................9 OVERVIEW ..................................................................................................................9 THE STUDY SITES ......................................................................................................12 STRUCTURE OF THE REPORT......................................................................................16 REFERENCES .............................................................................................................17 CHAPTER 2: FISHERY INDEPENDENT SURVEYS OF THE BY-CATCH OF THE SPENCER GULF PRAWN FISHING GROUNDS ......................................21 ABSTRACT ................................................................................................................22 INTRODUCTION .........................................................................................................23 MATERIALS AND METHODS ......................................................................................23 RESULTS ...................................................................................................................24 DISCUSSION ..............................................................................................................34 REFERENCES .............................................................................................................36 CHAPTER 3: POPULATION PARAMETERS OF KEY ELASMOBRANCH BY-CATCH SPECIES IN SPENCER GULF .........................................................39 SECTION I. GENERAL INTRODUCTION ..........................................................39 BACKGROUND...........................................................................................................40 Current knowledge of key elasmobranch by-catch species in Spencer Gulf .......42 Aims of this study .................................................................................................49 REFERENCES .............................................................................................................51 SECTION II. DIVERSITY, DISTRIBUTION AND ABUNDANCE ...................57 vii ABSTRACT ................................................................................................................58 INTRODUCTION .........................................................................................................59 MATERIALS AND METHODS ......................................................................................59 Sampling ..............................................................................................................59 Diversity...............................................................................................................60 Abundance............................................................................................................61 Data analysis .......................................................................................................61 RESULTS ...................................................................................................................62 Diversity...............................................................................................................62 Distribution..........................................................................................................62 Abundance............................................................................................................69 DISCUSSION ..............................................................................................................82 Diversity, richness and distribution.....................................................................82 Abundance............................................................................................................83 REFERENCES .............................................................................................................87 SECTION III. TAGGING AND MOVEMENT IN SPENCER GULF ...............89 ABSTRACT ................................................................................................................90 INTRODUCTION .........................................................................................................91 MATERIALS AND METHODS ......................................................................................91 Tagging ................................................................................................................91 Data analysis .......................................................................................................94 RESULTS ...................................................................................................................94 Recaptures............................................................................................................95 Site of tag attachment...........................................................................................98 Recapture site and rates.......................................................................................98 Distance travelled ................................................................................................99 Rate of displacement..........................................................................................101 Direction of movement.......................................................................................101 DISCUSSION ............................................................................................................105 Recapture rates ..................................................................................................105 Movement of Port Jackson sharks in Spencer Gulf ...........................................106 Implications for fishing fleet ..............................................................................107 Limitations to tagging studies............................................................................108 viii Site of tag attachment.........................................................................................109 Tag shedding......................................................................................................110 REFERENCES ...........................................................................................................110