R2006/823 l 30/06/2009 GHATF shark survey of population abundance and population size composition for target, byproduct and bycatch species GHATF shark survey of population abundance and population size composition for target, byproduct and bycatch species J. Matias Braccini, Terence I. Walker and Anne S. Gason Department of Primary Industries PO Box 114, Queenscliff, Victoria 3225 June 2009 © Australian Fisheries Management Authority and Primary Industries Research Victoria. 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. ISBN 978‐1‐74217‐386‐3 Preferred way to cite: Braccini, J. M., Walker, T. I., and Gason, A. S. (2009). GHATF shark survey of population abundance and population size composition for target, byproduct and bycatch species. Final report to Australian Fisheries Management Authority. Project No. R2006/823. June 2009. iv + 123 pp. (Fisheries Research Branch, Department of Primary Industries: Queenscliff, Victoria, Australia). Published by Department of Primary Industries, Fisheries Research Branch, Queenscliff, Victoria, 3225. DISCLAIMER The authors do not warrant that the information in this book is free from errors or omissions. The authors do not accept any form of liability, be it contractual, tortious or otherwise, for the contents of this book or for any consequences arising from its use or any reliance placed. upon it The information, opinions and advice contained in this book may not relate to, or be relevant to, a readerʹs particular circumstances. Opinions expressed by the authors are the individual opinions of those persons and are not necessarily those of the publisher or research provider. GHATF shark survey ii Table of Contents Non‐technical Summary...........................................................................................................................1 Acknowledgements...................................................................................................................................3 Background ................................................................................................................................................3 Need ................................................................................................................................................4 Objectives ................................................................................................................................................5 Methods ................................................................................................................................................5 Collection of data.......................................................................................................................................5 Catch rate comparisons.............................................................................................................................6 Post‐capture mortality...............................................................................................................................7 Estimating length‐frequency and age‐frequency structure of population .....................................8 Estimating total mortality ......................................................................................................................10 Results/Discussion ..................................................................................................................................10 Sampling summary .................................................................................................................................10 Catch rate comparisons...........................................................................................................................11 Commercial species.................................................................................................................................11 Bycatch species.........................................................................................................................................13 Size‐frequency composition of the catch ............................................................................................14 Retained and discarded species............................................................................................................15 Post‐capture mortality.............................................................................................................................15 Age‐frequency composition of the catch.............................................................................................15 Wildlife interactions ...............................................................................................................................16 Carcass damage ........................................................................................................................................16 Reproductive sampling ..........................................................................................................................16 Estimating size‐ and age‐structure of commercial shark populations ..........................................16 Estimating total mortality of gummy shark and school shark for each sex .................................17 Benefits / Management Outcomes........................................................................................................18 Conclusion ..............................................................................................................................................18 References ..............................................................................................................................................20 Supplements and Appendices ..............................................................................................................97 Appendix 1. Fishing sites for 2007–08 shark survey .........................................................................97 Appendix 2. Catch rate of commercial species caught in each surveys.......................................107 Appendix 3. Catch rate of bycatch species caught in each survey................................................121 GHATF shark survey iii List of Tables Table 1. Sampling summary for the 2007–08 survey 21 Table 2. Number of individuals and species caught during the 2007–08 survey 22 Table 3. Number of individuals of each species caught during the 2007–08 survey 23 Table 4. Between-survey comparisons of the number of individuals of commercial species 28 Table 5. Between-survey comparisons of the number of individuals of bycatch species 43 Table 6. Size-frequency composition of species caught in the 2007–08 survey 46 Table 7. Retained and discarded individuals caught in the 2007–08 survey. 53 Table 8. Retained and discarded individuals caught by mesh size in the 2007–08 survey. 54 Table 9. Post-capture mortality for the species caught in the 2007–08 survey 59 Table 10. Wildlife interactions in the 2007–08 survey 61 Table 11. Carcass damage from predation on commercial species 62 Table 12. Number of samples collected for reproduction during 2007–08 survey 63 Table 13. Gillnet relative length selectivity analysis for gummy shark (Mustelus antarcticus) during 1973–76 64 Table 14. Gillnet relative length selectivity analysis for gummy shark (Mustelus antarcticus) during 1986–87 65 Table 15. Gillnet relative length selectivity analysis for gummy shark (Mustelus antarcticus) during 2007–08 66 Table 16. Gillnet relative length selectivity analysis for school shark (Galeorhinus galeus) during 1986–87 67 Table 17. Gillnet relative length selectivity analysis for school shark (Galeorhinus galeus) during 2007–08 68 Table 18. Gillnet relative length selectivity analysis for common sawshark (Pristiophorus cirratus) during 2007–08 69 Table 19. Gillnet relative length selectivity analysis for southern sawshark shark (Pristiophorus nudipinnis) during 2007–08 70 Table 20. Gillnet relative length selectivity analysis for elephant fish (Callorhinchus milii) during 2007–08 71 Table 21. Gillnet relative age selectivity analysis for male gummy shark (Mustelus antarcticus) during 1986–87 72 Table 22. Gillnet relative age selectivity analysis for female gummy shark (Mustelus antarcticus) during 1986–87 73 Table 23. Gillnet relative age selectivity analysis for male school shark (Galeorhinus galeus) during 1986–87 74 Table 24. Gillnet relative age selectivity analysis for female school shark (Galeorhinus galeus) during 1986–87 75 Table 25. Gillnet relative age selectivity analysis for male gummy shark (Mustelus antarcticus) during 2007–08 76 Table 26. Gillnet relative age selectivity analysis for female gummy shark (Mustelus antarcticus) during 2007–08 77 Table 27. Gillnet relative age selectivity analysis for male school shark (Galeorhinus galeus) during 2007–08 78 Table 28. Gillnet relative age selectivity analysis for female school shark (Galeorhinus galeus) during 2007–08 79 Table 29. Summary of length and age at maximum selectivity for gummy and school shark 80 Table 30. Total mortality estimates for male gummy shark (Mustelus antarcticus) 1986–87 81 Table 31. Total mortality estimates for female gummy shark (Mustelus antarcticus) 1986–87 82 Table 32. Total mortality