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Influence of Environmental Factors on Population Structure of Arrow Squid Nototodarus Gouldi: Implications for Stock Assessment

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Influence of Environmental Factors on Population Structure of Arrow Squid Nototodarus Gouldi: Implications for Stock Assessment INFLUENCE OF ENVIRONMENTAL FACTORS ON POPULATION STRUCTURE OF ARROW SQUID NOTOTODARUS GOULDI: IMPLICATIONS FOR STOCK ASSESSMENT COREY PAUL GREEN, BAPPSC (FISHERIES) SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF TASMANIA OCTOBER 2011 Arrow squid Nototodarus gouldi (McCoy, 1888) (Courtesy of Robert Ingpen, 1974) FRONTISPIECE DECLARATION STATEMENT OF ORIGINALITY This thesis contains no material which has been accepted for a degree or diploma by the University or any other institution, except by way of background information and duly acknowledged in the thesis, and to the best of the my knowledge and belief no material previously published or written by another person except where due acknowledgement is made in the text of the thesis, nor does the thesis contain any material that infringes copyright. ………………………………………….…. 28th October 2011 Corey Paul Green Date AUTHORITY OF ACCESS This thesis may be made available for loan and limited copying in accordance with the Copyright Act 1968. ………………………………………….…. 28th October 2011 Corey Paul Green Date I ACKNOWLEDGEMENTS This thesis assisted in fulfilling the objectives of the Fisheries Research and Development Corporation Project No. 2006/012 ―Arrow squid — stock variability, fishing techniques, trophic linkages — facing the challenges‖. Without such assistance this thesis would not have come to fruition. Research on statolith element composition was kindly funded by the Holsworth Wildlife Research Endowment (HWRE), and provided much information on arrow squid lifecycles. The University of Tasmania (UTAS), the Victorian Marine Science Consortium (VMSC) and the Department of Primary Industries — Fisheries Victoria, assisted in providing laboratories, desks and utilities, as well as offering a wonderful and inviting working environment. I was fortunate enough to receive the VMSC Postgraduate of the Year Award in 2008 with prize money used to fund research and attend conferences. The UTAS Graduate Research Office and the HWRE provided financial assistance to attend at the Cephalopod International Advisory Council Symposium in Spain; whereas the Tasmanian Brach of the Australian Marine Science Association (AMSA) provided a student grant to attend the AMSA conference in 2009. I would like to thank my two co-supervisors, Prof. Natalie Moltschaniwskyj and Dr. Patti Virtue. They provided enormous scientific, managerial and administrative support. Their encouragement and willingness to help, kept me focused throughout the candidature. I‘m also grateful to George Jackson for establishing the FRDC project and giving me a wonderful opportunity to learn, experience, and enjoy many facets of a candidature. Thank you to Simon Wotherspoon for the numerous 1:00 am emails which explained statistical analyses in a logical manner. Simon Robertson was fundamental in providing advice and software for statolith shape analyses. Dr. Terry Walker has been highly influential by providing scientific advice and Dr. David Smith has provided direction and encouragement throughout my candidature and research career. Heidi Pethybridge was vital in providing supplementary information on ecosystem modelling and diet of arrow squid. Without the contribution and willingness from the commercial fishing sector, no squid would have been collected for this research. In particular, thanks go to II Tony Bennett (San Tangaroa), Lisle Ellaway (Veteran) and John Edgar (Jumanji); also operators of the fishing vessels Zeehaan, Moira Elizabeth, Silver Phoenix and Racovolis Fisheries for supplying arrow squid. The Australian Fisheries Management Authority, Graeme Cottier, Paul McCoy and Lauren Brown were pivotal in organising commercial fishing data and squid samples. Many other people are to be acknowledged for their involvement in laboratory processing and data collection including Andrew Brown, Ruth Casper, Alistair Hobday, Matt Koopman, Khyalla Morgan, Anne-Elise Nieblas, Tim Smith, Fabian Trinnie, Emma Woodcock and Kimberly Young. Dr. Paul Hamer and Dr. Jodie Kemp provided training and assistance in using the inductively couple plasma mass spectrophotometer used for statolith element analyses, and assisted in the extraction and interpretation of data. Allister Coots provided maps of sampling areas. I could not have completed this candidature without the inspiration and support from my parents and friends who often provided encouragement and advice when I needed it most. However, my greatest source of inspiration has come from my family. My amazing wife Sharon and two wonderful children, Montana (11) and Hamish (7), have endured so many of my ups and downs; however, have always given their unquestionable love, support and encouragement for which I‘m eternally grateful. III ABSTRACT As separate stocks within a fishery can function differently, ensuring sustainability of each is fundamental when establish or refining management regulations and relies on a firm comprehension of the biological, recruitment, growth, predator-prey, and mortality characteristics in response to environmental factors and fishing pressure. The aim of this study was to analyse the population structure, recruitment variability, migratory characteristics, and catch composition of the arrow squid Nototodarus gouldi collected in the Great Australian Bight (GAB) and Victoria from 2007 – 2009. Nototodarus gouldi is a common oceanic ommastrephid found in waters of southern Australia and are considered commercially and ecologically important. Although research on N. gouldi has already provided biological and population characteristics for fisheries assessments, better estimates of temporal and spatial variability of population structure and the processes responsible are required. Completing their lifecycle in less than one year, N. gouldi exhibited substantial variability in growth, spatial distribution, and recruitment; processes considered to be highly influenced by environment and oceanic factors such as water temperature and productivity. Comparing statolith shape and biological characteristics from squid collected in Victoria to squid collected in the GAB suggested significant phenotypic heterogeneity in stocks; whereas statolith elemental composition analysis indicated that N. gouldi caught at either location hatch throughout their distribution. Both male and female N. gouldi grew faster and were larger in cooler waters off Victoria compared with warmer waters of the GAB. The correlation of sea surface temperature (SST) with growth showed that juveniles experiencing greater SST resulted in slower growth in the GAB; however, juveniles experiencing greater SST had faster growth in Victoria. Distribution of hatch dates calculated from statolith age estimates suggested that N. gouldi collected in Victoria and the GAB during 2007 – 2009 hatch year round with peaks of greater recruitment. Comparing the catch composition of N. gouldi caught inshore from the jig fishery to squid caught offshore from the trawl fishery using measures of size and growth suggested that squid caught inshore by jiggers were larger, consisted of more males than females, and had a greater percentage of mature females. However, statolith elemental composition from N. gouldi collected at IV inshore and offshore locations was likely to be driven by uniform ocean water chemistry and squid physiological processes. Based on biology, reproductive, recruitment, and growth characteristics of N. gouldi found in southern Australia, current fishing effort is unlikely to jeopardize the sustainability of the resource. V TABLE OF CONTENTS 1. GENERAL INTRODUCTION ..................................................................................... 15 Population dynamics and assessment of fisheries resources .......................... 15 Fundamentals of fisheries stock assessment .................................................. 16 Importance, population dynamics, assessment, and sustainability of cephalopods .................................................................................................... 19 A review of Nototodarus gouldi biology and ecology — addressing the knowledge gaps ........................................................................................ 24 The Nototodarus gouldi fishery — History, techniques, and catch ............... 26 Assessment and management of the Nototodarus gouldi fishery .................. 30 Thesis aims and structure ............................................................................... 31 2. AN ANALYSIS OF SPATIAL AND TEMPORAL POPULATION STRUCTURE OF ARROW SQUID NOTOTODARUS GOULDI FROM SOUTHERN AUSTRALIA USING STATOLITH ELEMENTAL COMPOSITION AND SHAPE ................................................. 33 Abstract .......................................................................................................... 33 Introduction .................................................................................................... 34 Methods .......................................................................................................... 38 Results ............................................................................................................ 53 Discussion ...................................................................................................... 59 3. GROWTH AND REPRODUCTIVE VARIABILITY OF ARROW SQUID NOTOTODARUS GOULDI FROM SOUTHERN AUSTRALIAN WATERS IN RELATION TO ENVIRONMENTAL AND OCEANOGRAPHIC FACTORS ............................................ 68 Abstract
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