Habitat Modification and its Influence on Prawn and Crab Fisheries Dr Jason E. Tanner Final Report Project No. 98/208 i Habitat Modification and its Influence on Prawn and Crab Fisheries Jason E. Tanner (Editor) Published by SARDI Aquatic Sciences © Fisheries Research and Development Corporation and SARDI Aquatic Sciences 2002 This work is copyright. Except as permitted under the Copyright Act 1968 (Cth), no part of this reproduction 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 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, totious or otherwise, for the contents of this book or for any consequences arising from its use or any reliance placed upon it. 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ISBN 0 7308 5286 5 ii Contents: Non Technical Summary ................................................................................ v Acknowledgements: ..................................................................................... vii Background: .................................................................................................. vii Need: ............................................................................................................. viii Objectives: ..................................................................................................... ix Chapter 1: The influence of prawn trawling on benthic assemblages in Gulf St Vincent, South Australia. .............................................................. 1 Abstract ........................................................................................................ 1 Introduction .................................................................................................. 2 Methods ....................................................................................................... 3 Site description: ........................................................................................ 3 Experimental design: ................................................................................ 4 Statistical Methods: ................................................................................... 6 Results ......................................................................................................... 7 Discussion .................................................................................................. 15 Acknowledgments: ..................................................................................... 18 Literature cited ............................................................................................ 18 Chapter 2: Limited infaunal response to experimental trawling in previously untrawled areas. ......................................................................... 22 Abstract: ..................................................................................................... 22 Introduction ................................................................................................ 22 Materials and Methods ............................................................................... 24 Site selection .......................................................................................... 24 Experimental trawling ............................................................................. 24 Sampling ................................................................................................. 25 Statistical methods .................................................................................. 26 Results ....................................................................................................... 28 Multivariate analyses .............................................................................. 28 Univariate Analyses ................................................................................ 29 Discussion .................................................................................................. 32 Acknowledgments ...................................................................................... 34 References ................................................................................................. 34 Chapter 3: The influence of harvest refugia on penaeid prawn population dynamics and sustainable catch .............................................. 39 Abstract: ..................................................................................................... 39 Introduction: ............................................................................................... 39 Multi-habitat model ..................................................................................... 42 Results: ...................................................................................................... 45 Discussion: ................................................................................................. 51 Acknowledgments: ..................................................................................... 55 References: ................................................................................................ 55 Chapter 4: Stability of optimal harvest regime under stochastic variation in prawn demographic rates and fishing strategies. ................. 58 Abstract: ..................................................................................................... 58 Introduction ................................................................................................ 59 Methods ..................................................................................................... 60 Results ....................................................................................................... 62 iii Discussion .................................................................................................. 67 Acknowledgments ...................................................................................... 69 References ................................................................................................. 69 Chapter 5:The effect of effluent discharge on marine macrofauna in Gulf St Vincent, South Australia. ................................................................. 71 Abstract ...................................................................................................... 71 Introduction ................................................................................................ 72 Materials and Methods ............................................................................... 75 Study site ................................................................................................ 75 Spatial variation in fauna around Bolivar ................................................ 75 Temporal variation in fauna around Bolivar ............................................ 77 Water quality ........................................................................................... 78 Relationship between macrofaunal abundances and water quality ........ 78 Effects of nutrient enrichment on Penaeus latisulcatus growth ............... 78 Results ....................................................................................................... 80 Spatial variation in fauna around Bolivar ................................................ 80 Temporal variation in fauna around Bolivar ............................................ 90 Water Quality .......................................................................................... 92 Relationship between Macrofaunal Abundances and Water Quality ...... 93 Discussion .................................................................................................. 95 Spatial variation in fauna around Bolivar ................................................ 96 Temporal variation in fauna around Bolivar ............................................ 98 Water quality ........................................................................................... 99 Relationship between macrofaunal abundance and water quality ........ 100 Effect of nutrient enrichment on Penaeus latisulcatus growth .............. 100 Conclusion ............................................................................................ 101 Acknowledgments .................................................................................... 101 References ............................................................................................... 102 Chapter 6: Active habitat selection for sand by juvenile western king prawns, Melicertus latisulcatus (Kishinouye). ........................................ 109 Abstract: ................................................................................................... 109 Introduction: ............................................................................................. 110 Methods: .................................................................................................. 111 Results: ...................................................................................................