Population connectivity of Peltorhamphus novaezeelandiae between the neighbouring Otago and Southland regions of New Zealand. Patricia Mary Mockett A thesis submitted for the degree of Master of Science at the University of Otago, Dunedin, New Zealand. July 2013 ii Abstract Connectivity among subpopulations of organisms is a primary focus in marine ecology and this knowledge is particularly imperative to the development of regulations in the management of fisheries (Cowen et al., 2007). The structure of local populations can be identified using intrinsic markers such as morphological and life history characteristics, as well as genetic markers (Bailey, 1997, Begg and Waldman, 1999). Genetic techniques are limited in that they cannot detect low levels of exchange (Thresher, 1999). Life history, morphological and meristic characteristics have been regularly employed to identify differentiation between local populations and in order to create a robust study it is reccomended that a combination of traits be examined (Begg and Waldman, 1999). The objective of the present study is to determine the level of connectivity among subpopulations of the flatfish species Peltorhamphus novaezeelandiae in the neighbouring Otago and Southland regions of New Zealand. I endeavoured to determine whether these fish form a single panmictic population over this geographical landscape or, are in fact segregated into discrete sub- populations. Flatfish as a group are an important component in New Zealand’s annual commercial catch particularly in the Otago and Southland regions, yet there is little biological information available on each species including Peltorhamphus novaezeelandiae. Fish from each region were sampled by otter trawl and morphological, stable isotope, stomach content and age determination analyses were conducted. As a result of these analyses I concluded that Peltorhamphus novaezeelandiae exhibit a complex population structure within the Otago and Southland regions of New Zealand. These subpopulations experience connectivity whether it be via the dispersal and recruitment of eggs, larvae or juveniles or through the migration of adults. Subpopulations are subject to enough separation over spatial and temporal scales to enable and maintain significant differences in life history characteristics. It is evident that the population structure of P.novaezeelandiae occurs at smaller spatial scales than is currently recognised by the Quota Management System and it is hoped that the knowledge gained through the completion of this study enables more informed management decisions and the sustainability of this important fish stock. iii Acknowledgements Firstly, I would like to thank my supervisor Steve Wing for the extensive knowledge you have imparted on me during the development and completion of my thesis and to the University of Otago’s Marine Science Department which has given me the opportunity to meet some amazing people of whom I hope to never lose contact with. Early on in my thesis work I had the opportunity to travel to the National Fish Collection unit at Te Papa museum in Wellington where I was fortunate to meet collection manager, Andrew Stewart and visiting flatfish researcher from NOAA, Thomas Monroe. I would like to extend my sincere thanks to Tom as his knowledge and training in Peltorhamphus identification was invaluable. Your enthusiasm for the amazing world of flatfishes was very contagious. A special thanks to all staff at the Portobello Marine Lab, it was nice to see your smiling faces when I was getting frustrated with my work! To the Marine Studies Centre staff, I am grateful to have had the opportunity to work with you all and to be able to pursue my passion for all marine creatures while working in the aquarium. I even discovered that I enjoyed teaching much to my amazement. A big thank you to Ant Smith of the F.V Aurora, who went to immense trouble to collect fish required for this study, all of which were donated to me. And finally, to all of my family and friends who had lost hope that they would ever see the day that I finally submitted this thesis, my parents Debbie and Bruce Mockett, my In-laws Viv and Colin Adam. Thank you for your never ending support, there were times when I wanted to quit but you kept me going. To my dad Bruce, thank you for all your help in the field and the never ending discussions and requests for progress reports. To my loving husband Scott Adam, your ongoing enthusiasm for all marine creatures is my greatest encouragement of all and my involvement in your varied work history in the commercial fishing sector has enabled me to have some incredible experiences that I wouldn’t have had the opportunity to otherwise. Thank you for all of the hours you spent assisting me in fish collections, transporting animals back to the lab and frequent visits out to Portobello to feed them. This is just the beginning of many more adventures together. iv Table of contents Abstract ......................................................................................................................................... iii Acknowledgements ....................................................................................................................... iiv Table of contents............................................................................................................................. v List of figures ............................................................................................................................... ixx List of tables ................................................................................................................................... xi Chapter 1: GENERAL INTRODUCTION 1 1.1 Marine populations ............................................................................................................ 1 1.2 Population connectivity ..................................................................................................... 1 1.3 Identification of fish stocks ............................................................................................... 2 1.4 Techniques for identifying population connectivity and structure .................................... 3 1.5 Flatfish biology .................................................................................................................. 4 1.6 Peltorhamphus species ....................................................................................................... 5 1.7 Commercial interest and management .............................................................................. 5 1.8 Study Sites ........................................................................................................................ 8 1.8.1 Otago .......................................................................................................................... 8 1.8.2 Southland .................................................................................................................... 9 1.9 Objectives ....................................................................................................................... 10 Chapter 2: AGE AND GROWTH .............................................................................................. 11 2.1 Introduction ................................................................................................................... 11 2.1.1 The importance of age and growth in fisheries management................................... 11 2.1.2 Age determination using otoliths ............................................................................. 12 2.1.3 Forms of aging error ................................................................................................. 13 2.2 Objectives ....................................................................................................................... 15 2.3 Materials and Methods ................................................................................................. 16 2.3.1 Sample collection ..................................................................................................... 16 2.3.2 Otolith preparation for aging .................................................................................... 18 v 2.3.3 Age estimation...................................................................................................... 1919 2.3.4 Freezing Effects.................................................................................................... 1919 2.4 Data Analysis ............................................................................................................. 2222 2.4.1 Von Bertalanffy growth function 23 2.4.2 Growth curve comparison ........................................................................................ 23 2.5 Results ............................................................................................................................. 23 2.5.1 Length frequency and sex ratio ................................................................................ 23 2.5.2 Analysis of precision between readers ..................................................................... 26 2.5.3 Von Bertalanffy growth model ................................................................................ 27 2.6 Discussion ....................................................................................................................... 31 2.6.1 Aging precision between readers ............................................................................