RADIOMETRIC AGE VALIDATION AND SPATIAL DISTRIBUTION OF THE ANTARCTIC TOOTHFISH, (DISSOSTICHUS MAWSONI): IMPLICATIONS FOR A DEEP-SEA ANTARCTIC FISHERY A Thesis Presented to The Faculty of Moss Landing Marine Laboratories In Partial Fulfillment of the Requirements for the Degree Master of Science By Cassandra M. Brooks June, 2008 i © 2008 Cassandra M. Brooks ALL RIGHTS RESERVED ii ABSTRACT RADIOMETRIC AGE VALIDATION AND SPATIAL DISTRIBUTION OF THE ANTARCTIC TOOTHFISH, DISSOSTICUS MAWSONI: IMPLICATIONS FOR A DEEP-SEA ANTARCTIC FISHERY by Cassandra M. Brooks Antarctic toothfish (Dissostichus mawsoni) are subject to an increasingly important commercial fishery in the Southern Ocean, yet their life history characteristics and population structure remain largely unknown. In this study, Antarctic toothfish otoliths were obtained from American long-line fishing vessels in the Ross Sea, Antarctica. Age estimates obtained by counting annual growth increments in otolith sections indicate Antarctic toothfish live to at least 39 years of age. Lead-radium dating was used to validate ages up to 27.3 (range 21.7 -34.1) and provided support for ages up to 39 years of age using the methodology applied in this study. Validation also provided support for VBGF parameters, which indicate toothfish grow relatively slowly (k = 0.111; L∞ = 158.9; t0 = -0.605). Fish ages were then superimposed on a habitat map of the Ross Sea, Antarctica and broken into discrete spatial areas. Differences in age data within these areas was tested using ANOVA. There was a relationship between fish age and maturity increasing with depth; younger, less mature fish were more often found on the shallower continental shelf and older fish were more often found in the deeper regions on the continental slope. However, there was far more variability than expected and iv other oceanographic and ecological factors likely effect age structure distribution significantly. Older and most mature individuals were found on ridges in the northern Ross Sea, consistent with the hypothesis of an austral summer spawning migration. An effective management strategy might focus on protecting the northern ridge habitat to potentially maintain long-term viability of Antarctic toothfish populations. Additionally, Antarctic toothfish vital rates should be considered before expanding the Ross Sea fishery. v ACKNOWLEDGEMENTS This thesis would not have been possible without the help, encouragement and continued support of my mentors, colleagues, friends and family. A deep thanks to Dr. Gregor Cailliet who has been a wonderful teacher, advisor and mentor. Being his student has been a truly enjoyable experience and I thank him for always making time for me amidst the dozens of other students. My sincere appreciation goes out to Dr. Julian Ashford for constantly challenging me to understand the scientific process better. Working under him has given me invaluable insight into the ecology of toothfish and I thank him for his patience and continued support. My deepest gratitude goes out to Allen Andrews for being a simultaneous friend, mentor and colleague. Working with him has been a pleasure and I cannot thank him enough for all his encouragement, time and support, all of which led directly to my success as a student at MLML. Thanks to Dr. Gary Greene for providing insight on habitat and for his continued support. These four individuals, who all served on my thesis committee, have played a huge role in helping me become the scientist I am today. A warm thanks to Dr. Valerie Loeb and the entire AMLR crew for providing an amazing Antarctic experience, without which I may have never laid my eyes and hands (and chopsticks) on a live Antarctic toothfish. Special thanks to AMLR scientists Dr. Christian Reiss and Chris Jones. The age and growth portion of this study was made possible with the help of those at the CQFE lab at Old Dominion University. Special thanks to Nakul Ramanna for time put in reading otoliths and Karen Underkoffler for training me in the intricate details of sectioning toothfish otoliths. vi Thanks also to Craig Lundstrom for ICPMS processing of all samples. Deep gratitude to Dr. Brian Wells for providing invaluable insight into the world of statistics and for his continued friendship. Thanks to Bryan Dieter for his insight into the world of GIS and to Yusuf Sinan Husrevoglu at Old Dominion University for help in formatting my data. Without both of your help, the habitat portion of this study may not have been possible. Thanks to all the Antarctic toothfish scientists who have me obtain a better understanding of this species and its environment. Special thanks to Dr. Joe Eastman, and the folks at NIWA, including Peter Horn, Stuart Hanchet, Alistair Dunn and Dr. Malcom Francis. A heartfelt thanks to the folks at MLML who have now become dear life-long friends. Thanks to Elsie Tanadjaja for being my partner in all things beautiful and silly. Thanks to Tonatiuh Trejo for your continued love and support throughout my tenure at MLML. Thanks to Ashley Greenley for sharing in endless ridiculousness. Thanks to Berkeley Kauffman for your relentless friendship. Thanks also to Kristen Green, Phil Hoos and all the other wonderful members of the Moss Landing community that have offered their friendship and support. Special thanks to the members of the Ichthyology lab, the library staff, the IT staff and Shop guys. Thanks to the administrative staff, especially Kenneth Coale and Donna Kline. Thanks to the wonderful faculty and their contagious enthusiasm for teaching students about the marine science world. My deepest gratitude goes out to my entire immediate and extended family in New England. My eldest sister, Dr. Lisa Brooks, has always been an inspiration and vii role-model for me. I cannot thank her enough for her consistent positive support and celebration of my accomplishments. She is largely the reason I had the confidence to pursue graduate school and continues to be a strong and guiding force in my life. I thank both of my parents for working hard for the duration of their lives to afford me the opportunities of a good education and the freedom to choose my own career. I thank my mother for giving me a hard work ethic and for her continued support of my life choices. I thank my father for giving me incredible organization skills and a sense of adventure in all that I do. I thank the rest of my siblings, my nieces, and all of my extended family for their love and support. The age and growth portion of this project was funding by the National Science Foundation as part of the larger project “Collaborative Research: Age estimation of toothfish in support of radiometric age validation,” grant # 0232000. The habitat portion of this study was funded in part by NOAA’s Environmental Entrepreneurship Program. Additional funding was provided the Project Aware Foundation. viii PREFACE This thesis presents an application of lead-radium dating to the Antarctic toothfish which was further used to assess spatial age structure of this species in the Ross Sea, Antarctica. Chapter one provides an introduction to the Antarctic toothfish fishery, age and growth, lead-radium dating and the importance of habitat. Chapter two is the results of an age and growth study with radiometric age validation on Antarctic toothfish using lead-radium dating. Chapter three is a comprehensive geological history of the Ross Sea, Antarctica giving background regarding the processes that shape the seafloor habitat. Chapter four provides the habitat characterizations of the Ross Sea, Antarctica and the relationship between Antarctic toothfish life history and habitat. Both chapter two and four are in journal submission format; Canadian Journal of Fisheries and Aquatic Sciences is the intended journal for chapter two and the journal for chapter four has yet to be determined. ix CONTENTS PREFACE………………………………………………………………………………. ix LIST OF TABLES……………………………………………………………….......... xii LIST OF FIGURES…………………………………………………………………... xiii CHAPTER 1 – Introduction…………………………………………………………… 1 An important international resource……………………………………………... 1 Age and growth estimates………………………………………………………... 3 Lead-radium dating/Age validation……………………………………………… 6 The importance of habitat in life history………………………………………… 8 References……………………………………………………………………… 10 CHAPTER 2 – Age estimation and lead-radium dating of Antarctic toothfish…... 17 Abstract………………………………………………………………………… 17 Introduction……………………………………………………………………..18 Methods……………………………………………………………………….... 20 Estimation of age and precision using otolith growth zones…………… 20 Validation: Age-group determination and core extraction……………... 23 Validation: Radiometric analysis……………………………………….. 24 Statistical analysis………..…………………………………………...… 26 Results………………………………………………………………………….. 27 Estimation of age and precision………………………………………… 27 Radiometric analysis……………………………………………………. 28 Accuracy of age estimates……………………………………………… 29 Discussion…………………………………………………………………….... 30 Estimation of age and precision………………………………………… 30 Radiometric analysis……………………………………………………. 33 Accuracy of age estimates ……………………………………………... 35 Implications for management…………………………………………... 35 References……………………………………………………………………… 38 x CHAPTER 3 – Geological history of the Ross Sea, Antarctica…………………...... 55 Antarctic geological history…………………………………………………... 55 Ross Sea geological history…………………………………………….. 56 Ross Sea glaciology……………………………………………………………. 59 Sedimentation in the Ross Sea………………………………………………... 61 Sedimentation as recorded in