Sampling estuarine fish species for stock assessment C.A. Gray, B.C. Pease, S.L. StringfeUow, L.P. Raines, B.K. Rankin, T.R. Walford NSW Fisheries Research Institute P.O. Box 21, CronuUa, NSW, 2230 Australia .v.w, FISHEBIES RESEABCH & FISHERIES DE/ELOPHENT COBPGKOTCN FRDC Project No. 94/042 March 2000 NSW Fisheries Final Report Series No. 18 ISSN 1440-3544 Sampling estuarine fish species for stock assessment C.A. Gray, B.C. Pease, S.L. Stringfellow, L.P. Raines, B.K. Rankin, T.R. Walford Includes Appendices by D.J. Ferrell B.C. Pease, T.R. Walford G.N.G. Gordon, C.A. Gray, G.W. Liggins NSW Fisheries Research Institute P.O. Box 21, Cronulla, NSW, 2230 Australia FRDC Project No. 94/042 March 2000 NSW Fisheries Final Report Series No. 18 ISSN 1440-3544 Contents TABLE OF CONTENTS TABLE OF CONTENTS.................................................................................................................................! LIST OF TABLES......................................................................................................................................... IV LISTOFFIGURES.........................................................................................................................................V LIST OF APPENDICES............................................................................................................................... IX ACKNOWLEDEMENTS...............................................................................................................................X NON-TECHNICAL SUMMARY................................................................................................................. XI 1. INTRODUCTION.......................................................................................................................................! 1.1 BACKGROUND.......................................................................................................................................... 1 1.2 NEED........................................................................................................................................................4 1.3 OBJECTIVES .............................................................................................................................................5 1.4 ACHIEVEMENT OF OBJECTIVES.................................................................................................................5 2. SPATIAL AND TEMPORAL VARIATION IN RECRUITMENT AND GROWTH OF JUVENILE ESTUARINE FISHES......................................................................................................................................? 2.1 INTRODUCTION........................................................................................................................................? 2.2 METHODS.................................................................................................................................................? 2.2.7 Development of sampling strategy...................................................................................................7 2.2.2 Study locations and sampling procedure......................................................................................... 8 2.2.3 Analyses q/'fife)rto............................................................................................................................./0 2.3 RESULTS ................................................................................................................................................ 10 2.3.1 &»n^w/!;?/ng................................................................................................................................... ,0 2.3.2 Z)u^y?a^eac?................................................................................................................................ 76 2.3.3 fiream............................................................................................................................................. ,6 2.3.4 Tarwhine......................................................................................................................................... 16 2,3.5 LutfemA..........................................................................................................................................22 2.4 DISCUSSION ...........................................................................................................................................22 3. GENERAL PROCEDURES AND LOGISTICS OF SAMPLING FISHES IN THE NSW ESTUARINE COMMERCIAL FISHERY..................................................................................................35 3.1 INTRODUCTION .......................................................................................................................................35 3.2 STUDY LOCATIONS AND SAMPLING RATIONAL.......................................................................................35 3.3 SAMPLING FOR SIZE AND SEX COMPOSITION OF COMMERCIAL CATCHES................................................37 3.4 SAMPLING OF COMMERCIAL CATCHES FOR AGE COMPOSITION...............................................................37 3.5 DETERMINATION OF AGE AND GROWTH.................................................................................................39 3.5.1 Otolith preparation and reading....................................................................................................39 3.5.2 Determination of the age structure of commercial catches............................................................ 40 3.5.3 Estimation of growth models.......................................................................................................... 40 4. VARIATIONS W SIZE, SEX AND AGE COMPOSITIONS OF COMMERCIAL CATCHES OF YELLOWFIN BREAM (ACANTHOPAGRUS AUSTRALIS} IN NSW .....................................................41 4.1 SUMMARY OF RELEVANT ECOLOGICAL LITERATURE..............................................................................41 4.2 OVERVIEW OF THE NSW COMMERCIAL FISHERY...................................................................................42 4.3 AIMS OF THIS CHAPTER..........................................................................................................................45 4.4 METHODS..............................................................................................................................................45 4.5 RESULTS ................................................................................................................................................46 4.5.1 Variation in size and sex composition of commercial catches....................................................... 46 FRDC Project No. 94/042 Sampling estuarineflsh species for stock assessment Contents 4.5.2 Age determination.......................................................................................................................... 56 4.5.3 Variation in age structure of commercial catches.......................................................................... 59 4.5.4 Variation in size at age relationships and growth.......................................................................... 63 4.6 DISCUSSION ...........................................................................................................................................63 4.6.1 Age determination..........................................................................................................................63 4.6.2 Variations in size at age and growth..............................................................................................65 4.6.3 Variations in size, sex and age compositions of commercial catches ............................................ 65 4.6.4 Consequences for future monitoring programs of the commercial fishery.................................... 67 4.6.5 Conclusions and stock assessment considerations.......................................................................... 68 5. VARIATIONS IN SIZE, SEX AND AGE COMPOSITIONS OF COMMERCIAL CATCHES OF SAND WHITING (SILLAGO CILIATA) IN NSW.......................................................................................69 5.1 SUMMARY OF RELEVANT ECOLOGICAL LITERATURE..............................................................................69 5.2 OVERVIEW OF THE NSW COMMERCIAL FISHERY...................................................................................69 5.3 AIMS OF THIS CHAPTER..........................................................................................................................72 5.4 METHODS...............................................................................................................................................72 5.5 RESULTS ................................................................................................................................................72 5.5.7 Variation in size and sex composition of commercial catches.......................................................72 5.5.2 Age determination..........................................................................................................................80 5,5.3 Variation in age structure of commercial catches..........................................................................83 5.5.4 Variation in size at age and growth...............................................................................................83 5.6 DISCUSSION ...........................................................................................................................................83