Determination of the biological parameters required for managing the fisheries of four tuskfish species and western yellowfin bream Fairclough, D. V., Hesp S. A., Potter, I. C. & N. G. Hall Project No. 2000/137 Fisheries Research and Development Corporation Report FRDC project 2000/137 Determination of the biological parameters required for managing the fisheries of four tuskfish species and western yellowfin bream Fairclough D.V. Hesp S.A. Potter I.C. Hall N.G. June 2004 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. June 2004 ISBN: 0-646-39851-2 2 Table of Contents NON-TECHNICAL SUMMARY:............................................................................................6 OUTCOMES ACHIEVED TO DATE .......................................................................................6 ACKNOWLEDGEMENTS.......................................................................................................9 1.0 GENERAL INTRODUCTION .......................................................................................10 1.1 BACKGROUND ...................................................................................................10 1.2 NEED.....................................................................................................................13 1.3 OBJECTIVES........................................................................................................14 1.4 ADDITIONAL OBJECTIVES..............................................................................14 2.0 GENERAL MATERIALS AND METHODS................................................................15 2.1 STUDY AREAS....................................................................................................15 2.2 SAMPLING REGIME ..........................................................................................17 2.3 ENVIRONMENTAL MEASUREMENTS...........................................................18 2.4 FISH MEASUREMENTS.....................................................................................19 2.5 REPRODUCTIVE BIOLOGY..............................................................................19 2.6 AGE AND GROWTH...........................................................................................21 3.0 REPRODUCTIVE BIOLOGY OF ACANTHOPAGRUS LATUS ...............................23 3.1 INTRODUCTION .................................................................................................23 3.2 MATERIALS AND METHODS ..........................................................................25 3.2.1 Hermaphroditism of Acanthopagrus latus.............................................................25 3.2.2 Potential annual fecundity.....................................................................................27 3.2.3 Biomass and egg per recruit analysis....................................................................28 3.3 RESULTS..............................................................................................................29 3.3.1 Macroscopic and histological observations of gonad tissues ...............................29 3.3.2 Seasonal changes in gonadal categories with increasing length and age ............33 3.3.3 Proportions of juveniles, males and females immediately prior to and during the spawning period ....................................................................................................37 3.3.4 Reproductive variables..........................................................................................40 3.3.5 Fecundity ...............................................................................................................43 3.3.6 Spawning biomass per recruit ...............................................................................45 3.4 DISCUSSION........................................................................................................47 3.4.1 Acanthopagrus latus is a protandrous hermaphrodite ..........................................47 3.4.2 Aspects of spawning and estimates of fecundity....................................................49 3.4.3 Implications for management ................................................................................50 4.0 AGE AND SIZE COMPOSITIONS, GROWTH, MORTALITY AND HABITATS OF ACANTHOPAGRUS LATUS.....................................................................................52 4.1 INTRODUCTION .................................................................................................52 4.2 MATERIALS AND METHODS ..........................................................................54 4.2.1 Natural mortality ...................................................................................................54 4.2.2 Total mortality .......................................................................................................55 4.2.3 Integrating the separate mortality estimates.........................................................58 4.3 RESULTS..............................................................................................................60 4.3.1 Comparisons between the number of opaque zones on whole and sectioned otoliths ...................................................................................................................60 4.3.2 Validation that opaque zones are formed annually...............................................60 4.3.3 Length-frequency distributions of the different age classes ..................................62 4.3.4 Length-frequency distributions in different habitats .............................................62 4.3.5 Growth of Acanthopagrus latus .............................................................................65 4.3.6 Mortality estimates and year class strengths ........................................................65 3 4.4 DISCUSSION........................................................................................................72 4.4.1 Age and growth of Acanthopagrus latus................................................................72 4.4.2 Estimates of mortality............................................................................................73 5.0 REPRODUCTIVE BIOLOGY OF THE FOUR TUSKFISH SPECIES ....................76 5.1 INTRODUCTION .................................................................................................76 5.2 MATERIALS AND METHODS ..........................................................................79 5.2.1 Hermaphroditism of the four species of tuskfish..........................................................79 5.2.2 Lengths and ages at sexual maturity and sex change............................................80 5.2.3 Fecundity ...............................................................................................................81 5.3 RESULTS..............................................................................................................83 5.3.1 Histological evidence for hermaphroditism ..........................................................83 5.3.2 Sex ratios ...............................................................................................................85 5.3.3 Reproductive variables..........................................................................................87 5.3.4 Lengths and ages at maturity and sex change.......................................................94 5.3.5 Fecundity .............................................................................................................103 5.4 DISCUSSION......................................................................................................107 5.4.1 Evidence for hermaphroditism ............................................................................107 5.4.2 Spawning periods ................................................................................................108 5.4.3 Lengths and ages at maturity...............................................................................109 5.4.4 Comparisons between Choerodon rubescens in Shark Bay and the Abrolhos Islands..................................................................................................................110 5.4.5 Fecundity .............................................................................................................111 5.4.6 Management implications....................................................................................112 6.0 AGE COMPOSITIONS AND GROWTH OF THE FOUR TUSKFISH SPECIES 113 6.1 INTRODUCTION ...............................................................................................113 6.2 MATERIALS AND METHODS ........................................................................114 6.3 RESULTS............................................................................................................114 6.3.1 Length-weight relationships ................................................................................114 6.3.2 Validation of annual growth zone formation in otoliths and determination of birth dates.....................................................................................................................115