Fisheries Research Report No. 228, 2012 Biology and stock status of inshore demersal scalefish indicator species in the Gascoyne Coast Bioregion R. Marriott, G. Jackson, R. Lenanton, C. Telfer, E. Lai, P. Stephenson, C. Bruce, D. Adams and J. Norriss Fisheries Research Division Western Australian Fisheries and Marine Research Laboratories PO Box 20 NORTH BEACH, Western Australia 6920 Correct citation: Marriott, R., Jackson, G., Lenanton, R., Telfer, C., Lai, E., Stephenson, P., Bruce, C., Adams, D. and Norriss, J. (2012) Biology and stock status of inshore demersal scalefish indicator species in the Gascoyne Coast Bioregion. Fisheries Research Report No. 228. Department of Fisheries, Western Australia. 216pp. Enquiries: WA Fisheries and Marine Research Laboratories, PO Box 20, North Beach, WA 6920 Tel: +61 8 9203 0111 Email: [email protected] Website: www.fish.wa.gov.au ABN: 55 689 794 771 A complete list of Fisheries Research Reports is available online at www.fish.wa.gov.au © Department of Fisheries, Western Australia. July 2012. ISSN: 1035 - 4549 ISBN: 978-1-921845-13-0 ii Fisheries Research Report [Western Australia] No. 228, 2012 Contents Executive Summary .............................................................................................................. 1 Summary ........................................................................................................................ 4 Acknowledgements ........................................................................................................ 4 1.0 Introduction .................................................................................................................. 6 1.1 Background ............................................................................................................. 6 1.2 Indicator species approach ..................................................................................... 8 1.3 Need ........................................................................................................................ 8 1.4 Objectives .............................................................................................................. 9 2.0 The Gascoyne Marine Environment .......................................................................... 10 3.0 The Gascoyne Fishery and Management Arrangements ......................................... 11 3.1 Spatial management and jurisdictions .................................................................... 11 3.2 Commercial ........................................................................................................... 11 3.3 Recreational ............................................................................................................ 13 3.4 Charter .................................................................................................................... 14 3.5 Indigenous .............................................................................................................. 14 4.0 General methods ........................................................................................................... 15 4.1 Sample collection ................................................................................................... 15 4.1.1 Fishery-dependent methods ......................................................................... 15 4.1.2 Fishery-independent methods ....................................................................... 16 4.2 Sample processing .................................................................................................. 17 4.2.1 Otoliths ......................................................................................................... 17 4.2.2 Gonads .......................................................................................................... 19 4.3 Logbook data collection ......................................................................................... 19 4.4 Analyses – Rationale for spatial and temporal grouping of data ........................... 20 4.5 Analyses – Rationale for adopting different assessment approaches for the different indicator species ..................................................................................................... 22 5.0 Biological characteristics of key indicator species ..................................................... 24 5.1 Pink snapper ........................................................................................................... 24 5.1.1 Distribution, structure and movement ......................................................... 24 5.1.2 Age and growth ............................................................................................ 25 5.1.2.1 Introduction ............................................................................................... 25 5.1.2.2 Methods ..................................................................................................... 25 5.1.2.3 Results ....................................................................................................... 25 5.1.2.3.1 Contribution of samples from each sector ........................................... 25 5.1.2.3.2 Bias and precision ............................................................................... 26 5.1.2.3.3 Validation ............................................................................................. 27 5.1.2.3.4 Length and age composition of stock ................................................. 27 5.1.2.3.5 Growth ................................................................................................. 30 5.1.2.3.6 Natural mortality ................................................................................ 31 5.1.3 Recruitment .................................................................................................. 33 5.1.4 Reproduction ............................................................................................... 35 5.1.4.1 Introduction ............................................................................................... 35 5.1.4.2 Methods ..................................................................................................... 35 5.1.4.3 Results ....................................................................................................... 35 Fisheries Research Report [Western Australia] No. 228, 2012 iii 5.1.4.3.1 Annual reproductive cycles ................................................................. 35 5.1.4.3.2 Length and age at maturity .................................................................. 36 5.1.4.3.3 Fecundity ............................................................................................. 39 5.1.5 Other factors influencing susceptibility to exploitation ............................... 40 5.2 Spangled emperor .................................................................................................. 42 5.2.1 Distribution, structure and movement .......................................................... 42 5.2.2 Age and growth ............................................................................................ 42 5.2.2.1 Introduction ............................................................................................... 42 5.2.2.2 Methods ..................................................................................................... 43 5.2.2.3 Results ....................................................................................................... 43 5.2.2.3.1 Contribution of samples from each sector ........................................... 43 5.2.2.3.2 Bias and precision ................................................................................ 45 5.2.2.3.3 Validation ............................................................................................. 45 5.2.2.3.4 Length and age composition of stock .................................................. 45 5.2.2.3.5 Growth ................................................................................................. 49 5.2.2.3.6 Natural mortality ................................................................................. 50 5.2.2.4 Discussion.................................................................................................. 51 5.2.3 Recruitment .................................................................................................. 51 5.2.4 Reproduction ................................................................................................ 52 5.2.4.1 Introduction ............................................................................................... 52 5.2.4.2 Methods ..................................................................................................... 53 5.2.4.3 Results ....................................................................................................... 53 5.2.4.4 Discussion.................................................................................................. 55 5.2.5 Other factors influencing susceptibility to exploitation ............................... 55 5.3 Goldband snapper .................................................................................................. 56 5.3.1 Distribution, structure and movement .......................................................... 56 5.3.2 Age and growth ............................................................................................ 56 5.3.2.1 Introduction ..............................................................................................