Inland Waters and Catchment Ecology Diet and trophic characteristics of mulloway (Argyrosomus japonicus), congolli (Pseudaphritis urvillii) and Australian salmon (Arripis truttaceus and A. trutta) in the Coorong George Giatas and Qifeng Ye SARDI Publication No. F2015/000479-1 SARDI Research Report Series No. 858 SARDI Aquatics Sciences PO Box 120 Henley Beach SA 5022 September 2015 Giatas and Ye (2015) Diet of three fish species in the Coorong Diet and trophic characteristics of mulloway (Argyrosomus japonicus), congolli (Pseudaphritis urvillii) and Australian salmon (Arripis truttaceus and A. trutta) in the Coorong George Giatas and Qifeng Ye SARDI Publication No. F2015/000479-1 SARDI Research Report Series No. 858 September 2015 II Giatas and Ye (2015) Diet of three fish species in the Coorong This publication may be cited as: Giatas, G.C. and Ye, Q. (2015). Diet and trophic characteristics of mulloway (Argyrosomus japonicus), congolli (Pseudaphritis urvillii) and Australian salmon (Arripis truttaceus and A. trutta) in the Coorong. South Australian Research and Development Institute (Aquatic Sciences), Adelaide. SARDI Publication No. F2015/000479-1. SARDI Research Report Series No. 858. 81pp. South Australian Research and Development Institute SARDI Aquatic Sciences 2 Hamra Avenue West Beach SA 5024 Telephone: (08) 8207 5400 Facsimile: (08) 8207 5406 http://www.pir.sa.gov.au/research DISCLAIMER The authors warrant that they have taken all reasonable care in producing this report. The report has been through the SARDI internal review process, and has been formally approved for release by the Research Chief, Aquatic Sciences. Although all reasonable efforts have been made to ensure quality, SARDI does not warrant that the information in this report is free from errors or omissions. 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Cover photo: Congolli (Chris Bice) Printed in Adelaide: September 2015 SARDI Publication No. F2015/000479-1 SARDI Research Report Series No. 858 Author(s): George Giatas and A/Prof Qifeng Ye Reviewer(s): Chris Bice (SARDI) and Paul McEvoy (DEWNR) Approved by: Prof Xiaoxu Li - Science Leader - Aquaculture Signed: Date: 8 September 2015 Distribution: SAASC Library, University of Adelaide Library, Parliamentary Library, State Library and National Library Circulation: Public Domain III Giatas and Ye (2015) Diet of three fish species in the Coorong TABLE OF CONTENTS TABLE OF CONTENTS ............................................................................................................ IV ACKNOWLEDGEMENTS ....................................................................................................... VIII EXECUTIVE SUMMARY ........................................................................................................... 1 GENERAL INTRODUCTION ...................................................................................................... 4 PART 1 STOMACH-CONTENT ANALYSIS ........................................................................... 7 1.1 Mulloway ...................................................................................................................... 7 1.1.1 Biology and ecology .......................................................................................... 7 1.1.2 Species-specific aims and hypotheses .............................................................. 8 1.1.3 Methods ............................................................................................................ 8 1.1.4 Results .............................................................................................................14 1.1.5 Discussion ........................................................................................................19 1.2 Congolli .......................................................................................................................22 1.2.1 Biology and ecology .........................................................................................22 1.2.2 Species-specific aims and hypotheses .............................................................23 1.2.3 Methods ...........................................................................................................23 1.2.4 Results .............................................................................................................26 1.2.5 Discussion ........................................................................................................33 1.3 Australian salmon .......................................................................................................37 1.3.1 Biology and ecology .........................................................................................37 1.3.2 Species-specific aims and hypotheses .............................................................38 1.3.3 Methods ...........................................................................................................38 1.3.4 Results .............................................................................................................39 1.3.5 Discussion ........................................................................................................42 PART 2 STABLE ISOTOPE ANALYSIS OF COORONG FOOD-WEB ..................................44 2.1 Background.................................................................................................................44 2.2 Methods ......................................................................................................................44 2.3 Results ........................................................................................................................45 2.3.1 Food-web structure and trophic guilds ..............................................................45 2.3.2 Trophic position and fish diet estimation ...........................................................48 2.4 Discussion ..................................................................................................................50 2.4.1 Food-web structure and trophic guilds ..............................................................50 IV Giatas and Ye (2015) Diet of three fish species in the Coorong 2.4.2 Fish diet estimation ..........................................................................................51 2.4.3 Limitations and further research .......................................................................54 PART 3 GENERAL DISCUSSION ........................................................................................56 3.1 Summary of findings ...................................................................................................56 3.2 Comparison to drought ...............................................................................................56 3.2.1 Mulloway ..........................................................................................................56 3.2.2 Congolli ............................................................................................................58 3.2.3 Trophic structure ..............................................................................................58 3.3 Conclusions and management implications ................................................................59 REFERENCES .........................................................................................................................62 APPENDICES ...........................................................................................................................70 V Giatas and Ye (2015) Diet of three fish species in the Coorong LIST OF FIGURES Figure 1. Map of sampling sites in the Coorong and Lower Lakes.............................................. 9 Figure 2. Mid-water salinities of sampling sites in the Coorong during the different months. .....11 Figure 3. Two dimensional MDS ordination of the dietary compositions of three size classes (Small = <400 mm, Medium = 400–700 mm, Large = >700 mm) of mulloway from the Murray Estuary and North Lagoon of the Coorong.. ..............................................................................17 Figure 4. Two dimensional MDS ordination of the dietary compositions of two size classes (Small = <80 mm, Large = >80 mm) of congolli at three sites within the Coorong. ....................29 Figure 5. Importance of prey categories (% index of relative importance, IRI) in small (<80 mm) and large (>80 mm) congolli diet at three sites in the Coorong.. ................................................32 Figure 6. Importance of prey categories (% index of relative importance, IRI) for the two different species of Australian salmon in the Coorong.. ..........................................................................41 Figure 7. Stable nitrogen (δ15N) and carbon (δ13C) isotope signatures