STABLE ISOTOPE ANALYSIS OF RIVERS INLET SOCKEYE SALMON (ONCORHYNCHUS NERKA): INVESTIGATING THE CONTRIBUTION OF ENVIRONMENTAL CONDITIONS IN THE HIGH SEAS TO BRITISH COLUMBIA POPULATION DECLINES by Yago Doson Coll A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Resource Management and Environmental Studies) THE UNIVERISTY OF BRITSH COLUMBIA (Vancouver) May 2015 © Yago Doson Coll, 2015 Abstract Sockeye salmon (Oncorhynchus nerka) populations in BC have undergone varying degrees of decline coinciding with a shift to a warmer phase of the Pacific Decadal Oscillation (PDO) in 1977. The PDO, and other climate cycles, have been shown to significantly affect the physical and biological characteristics of the North East Pacific Ocean. Changes in ocean productivity have implications for pelagic food webs and may cause shifts in the abundance of potential prey for sockeye salmon, impacting their long-term production patterns. We investigated the coupling of ocean conditions and population fluctuations using Rivers Inlet as a case study, a system that suffered probably the most catastrophic sockeye stock collapse in BC history. Stable isotope analysis was used to access information on ocean conditions stored in the carbon and nitrogen isotope ratios of archived sockeye scales for the period 1915-2013. Our results indicated that Rivers Inlet sockeye salmon experienced highly variable open ocean conditions during this period. Both decadal scale shifts in North Pacific climate (e.g., PDO) and interannual scale shifts in climate (e.g., El Niño/La Niña events) were reflected in the physical and biological environment of the offshore Gulf of Alaska. Positive phases of the PDO and El Niño events were associated with a warmer and less productive ocean, while negative phases of the PDO and La Niña events were associated with a colder and more productive ocean. Moreover, the carbon and nitrogen stable isotope time-series indicated that the foraging habits of Rivers Inlet sockeye salmon were affected by these shifts of North Pacific climate. A lengthening (shortening) of the food web was associated to warm (cold) and less productive (more productive) periods. In addition, the isotope data also supports Rivers Inlet sockeye salmon shifting diet depending upon prey availability. We concluded that a combination of the ii two factors was responsible for the changes in the feeding ecology of Rivers Inlet sockeye salmon during the period 1915-2013. Such variation in the feeding ecology of Rivers Inlet sockeye salmon could potentially have a negative effect in the overall survival rates of sockeye salmon. iii Preface This thesis is the result of a long journey that started four years ago. Both my supervisor Dr. Evgeny Pakhomov and co-supervisor Dr. Brian Hunt started the work for this thesis way before I did. They proposed the research topic, applied for funding and made all the arrangements needed in order to obtain all tissue samples and perform the stable isotope analysis. The collaboration of the Department of Fisheries and Oceans Canada (DFO) and the Wuikinuxv Nation was vital to obtain all the tissue samples used in this study. Dr. Sven Kaehler at the IsoEnvironmental lab in Rhodes University performed the stable isotope analysis, providing the isotope ratios of Rivers Inlet sockeye salmon scales for us to interpret. The amount of hours that I spent gathering and reading scientific literature, running statistical analyses, and interpreting the resulting data were not as surprising as the amount of hours I spent trying to figure out how to structure every paragraph of this thesis. To anyone reading this, if you ever have trouble to figure out a problem and you cannot think of a good idea on how to approach it, go outside for a walk, a run or a cycle. I had the most brilliant ideas while riding my bike. iv Table of contents Abstract ......................................................................................................................................................... ii Preface ......................................................................................................................................................... iv Table of contents .......................................................................................................................................... v List of tables ................................................................................................................................................. vii List of figures ............................................................................................................................................... viii Acknowledgements ....................................................................................................................................... x Dedication .................................................................................................................................................... xii 1 Introduction .......................................................................................................................................... 1 2 Materials and methods ....................................................................................................................... 15 2.1 Overview of study site and Owikeno sockeye stock. .................................................................. 15 2.2 Sample collection ........................................................................................................................ 17 2.2.1 Archived samples ................................................................................................................ 17 2.2.2 Recent samples ................................................................................................................... 18 2.3 Sample preparation .................................................................................................................... 20 2.4 Measurement of stable isotopes ................................................................................................ 21 2.4.1 13C correction for Suess Effect .......................................................................................... 21 2.4.2 13C correction for C:N ........................................................................................................ 22 2.4.3 Muscle and scale isotopic offset ......................................................................................... 26 2.5 Statistical analyses ...................................................................................................................... 26 2.6 Principal component analysis (PCA) ............................................................................................ 27 2.6.1 Data and methods. .............................................................................................................. 28 2.7 Additional data sets .................................................................................................................... 32 2.7.1 Baseline Isotope data. ......................................................................................................... 32 2.7.2 Nutrient data. ...................................................................................................................... 33 3 Results ................................................................................................................................................. 34 3.1 Comparison of 2013 pre-spawn and post-spawn samples ......................................................... 34 3.2 Isotopic relatioship between muscle and scale tissue ................................................................ 42 3.3 Carbon and nitrogen stable isotope time-series from rivers inlet sockeye salmon scales ......... 47 3.4 Principal component analysis (PCA) ............................................................................................ 52 3.4.1 PCA on the 33 environmental time-series (PCAenv) ............................................................ 52 v 3.4.2 PCA on the 15 physical time-series (PCAphys) ...................................................................... 57 3.4.3 PCA on the 18 biological time-series (PCAbiol) ..................................................................... 60 3.5 Relationships between environmental conditions and stable isotope time-series.................... 64 3.6 Baseline isotopic data ................................................................................................................. 66 3.7 Nutrient data ............................................................................................................................... 68 4 Discussion ............................................................................................................................................ 70 4.1 Comparison of pre-spawn and post-spawn isotope data: physiological implications ............... 70 4.2 Isotopic relationship between muscle and scale tissue .............................................................. 72 4.3 Principal component analysis (PCA) ............................................................................................ 73 4.4 Stable isotope variability ............................................................................................................. 75 4.5 Stable isotopes and climate shifts