Biological and fisheries data for managing the deep-sea crabs Hypothalassia acerba and Chaceon bicolor in Western Australia Smith, K.D., Potter, I.C. and Hall, N.G. Projects No. 1999/154 and 2001/055 Fisheries Research and Development Corporation Report FRDC projects 1999/154 and 2001/055 Fisheries Research and Development Corporation Report FRDC projects 1999/154 and 2001/055 FINAL REPORT Biological and fisheries data for managing the deep-sea crabs Hypothalassia acerba and Chaceon bicolor in Western Australia Smith, K. D. Potter,I.C. Hall, N. G. September 2004 ISBN: 0-86905-883-5 Centre for Fish and Fisheries Research Murdoch University Murdoch, Western Australia 6150 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. 2 Table of Contents NON-TECHNICAL SUMMARY: ........................................................................................8 ACKNOWLEDGEMENTS.................................................................................................10 1.0 GENERAL INTRODUCTION .............................................................................11 1.1 THE CHAMPAGNE CRAB HYPOTHALASSIA ACERBA.......................................... 11 1.2 THE CRYSTAL CRAB CHACEON BICOLOR.......................................................... 11 1.3 PREVIOUS BIOLOGICAL STUDIES ON DEEP-SEA CRABS ................................ 13 1.4 NEED ........................................................................................................................ 14 2.0 GENERAL MATERIALS AND METHODS.......................................................16 2.1 SAMPLING OF HYPOTHALASSIA ACERBA ............................................................ 16 2.1.1 Depth-stratified sampling regime.................................................................... 16 2.1.2 Onboard sampling of commercial catches of Hypothalassia acerba.................22 2.1.3 Structure of traps used in the commercial fishery to catch Hypothalassia acerba. .......................................................................................................................22 2.1.4 Tagging of Hypothalassia acerba.....................................................................23 2.1.5 Sampling of Chaceon bicolor ..........................................................................23 2.1.6 Structure of traps used in the commercial fishery to catch Chaceon bicolor ....24 2.2 MEASUREMENTS ................................................................................................... 25 2.2.1 Water temperatures.........................................................................................25 2.2.2 Data recorded for crabs..................................................................................25 3.0 THE FISHERIES FOR HYPOTHALASSIA ACERBA AND CHACEON BICOLOR .............................................................................................................................29 3.1 INTRODUCTION...................................................................................................... 29 3.2 MATERIALS AND METHODS ................................................................................ 30 3.2.1 Data on commercial catches...........................................................................30 3.2.2 Onboard collection of data ............................................................................. 30 Chaceon bicolor.............................................................................................................31 3.2.3 Data Analysis .................................................................................................32 3.3 RESULTS .................................................................................................................. 33 3.3.1 Commercial catch and effort data for Hypothalassia acerba............................33 3.3.2 Commercial catch and effort data for Chaceon bicolor ...................................41 3.3.3 Analysis of catches and sizes of crabs derived from onboard sampling ...........41 3.3.4 Carapace Lengths........................................................................................... 49 3.3.5 Carapace lengths of Chaceon bicolor in non-meshed and meshed traps ..........53 3.3.6 Results from release of tagged Hypothalassia acerba.......................................54 3.4 DISCUSSION ............................................................................................................ 54 3.4.1 Annual trends in catch statistics......................................................................54 3.4.2 Monthly trends in catch statistics .................................................................... 57 3.4.3 Catches and carapace lengths of Hypothalassia acerba and Chaceon bicolor ..58 4.0 RELATIVE ABUNDANCES AND SIZE COMPOSITIONS OF HYPOTHALASSIA ACERBA ON TWO COASTS AND IN DIFFERENT WATER DEPTHS AND SEASONS ...................................................................................................59 4.1 INTRODUCTION...................................................................................................... 59 3 4.2 MATERIALS AND METHODS ................................................................................ 61 4.3 RESULTS .................................................................................................................. 64 4.3.1 Water temperature..........................................................................................64 4.3.2 Relative abundance of crabs in different water depths and temperature ..........64 4.3.3 Relationship between carapace length and water depth, coast and season ...... 69 4.3.4 Sex ratios........................................................................................................74 4.3.5 Results of enclosing traps with mesh...............................................................75 4.4 DISCUSSION ............................................................................................................ 75 4.4.1 Relationship between catch rates and water depth ..........................................75 4.4.2 Relationship between catch rates and water temperature................................ 79 4.4.3 Trap selectivity ...............................................................................................80 5.0 COMPARISONS BETWEEN THE REPRODUCTIVE BIOLOGY OF FEMALES OF TWO SPECIES OF DEEP SEA CRABS WHICH LIVE IN DIFFERENT WATER DEPTHS ...............................................................................................................81 5.1 INTRODUCTION...................................................................................................... 81 5.2 MATERIALS AND METHODS ................................................................................ 83 5.2.1 Collection of samples......................................................................................83 5.2.2 Laboratory processing....................................................................................83 5.3 RESULTS .................................................................................................................. 85 5.3.1 Ovarian maturation stages..............................................................................85 5.3.2 Monthly trends in reproductive indices ........................................................... 89 5.4 DISCUSSION ............................................................................................................ 98 5.4.1 Comparisons between Hypothalassia acerba on the west and south coasts ......98 5.4.2 Comparisons between Hypothalassia acerba and Chaceon bicolor ................101 5.4.3 Investment in gonadal development by Hypothalassia acerba ........................102 6.0 POTENTIAL BIAS IN ESTIMATES OF THE SIZE OF MATURITY OF CRABS DERIVED FROM TRAP SAMPLES .................................................................104 6.1 INTRODUCTION.................................................................................................... 104 6.2 MATERIAL AND METHODS ................................................................................ 106 6.2.1 Sampling and measurement of crabs.............................................................106 6.2.2 Data analysis................................................................................................ 108 6.3 RESULTS ................................................................................................................ 108 6.3.1 Size composition ...........................................................................................108 6.3.2 Size at maturity.............................................................................................110 6.4 DISCUSSION .......................................................................................................... 114 7.0 DO THE CHELAE OF THE MALES OF THREE CRAB SPECIES UNDERGO ALLOMETRIC CHANGES THAT CAN BE USED TO DETERMINE MORPHOMETRIC MATURITY? ..................................................................................117 7.1 INTRODUCTION.................................................................................................... 117 7.2 MATERIAL AND METHODS ...............................................................................