UNIVERSITY OF CALIFORNIA SANTA CRUZ ILLUMINATING THE TWILIGHT ZONE: DIET AND FORAGING STRATEGIES OF A DEEP-SEA PREDATOR, THE NORTHERN ELEPHANT SEAL A dissertation submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in ECOLOGY AND EVOLUTIONARY BIOLOGY by Chandra Goetsch December 2018 The Dissertation of Chandra Goetsch is approved: _________________________________ Professor Daniel P. Costa, Chair _________________________________ Professor Pete Raimondi _________________________________ Dr. Elliott L. Hazen _________________________________ Professor Raphael M. Kudela _________________________________ Lori Kletzer Vice Provost and Dean of Graduate Studies Copyright © by Chandra Goetsch 2018 TABLE OF CONTENTS LIST OF TABLES ...................................................................................... vii LIST OF FIGURES...................................................................................... ix ABSTRACT .............................................................................................. xiv ACKNOWLEDGEMENTS ......................................................................... xvii DEDICATION ......................................................................................... xxvi INTRODUCTION ..........................................................................................1 Broad Context ......................................................................................................... 1 Dissertation Summary ............................................................................................ 5 References ................................................................................................................ 8 CHAPTER 1: Energy-Rich Mesopelagic Fishes Revealed as a Critical Prey Resource for a Deep-Diving Predator using Quantitative Fatty Acid Signature Analysis.........................................................................13 1.1 Abstract............................................................................................................ 13 1.2 Introduction ..................................................................................................... 14 1.3 Materials and Methods ................................................................................... 18 1.3.1 Ethics Statement......................................................................................... 19 1.3.2 Field Methods ............................................................................................ 19 Elephant seal sampling................................................................................. 19 Collecting the prey library ........................................................................... 20 1.3.3 Prey Classification ..................................................................................... 21 1.3.4 Lipid Analysis ............................................................................................ 23 Lipid extraction ............................................................................................ 23 Gas chromatography and FA profiles .......................................................... 24 Fatty acid subset ........................................................................................... 25 1.3.5 QFASA Diagnostics................................................................................... 25 Calculation of calibration coefficients ......................................................... 26 iii Predator FA values outside the range of the prey ........................................ 27 Prey library reduction .................................................................................. 27 Non-metric dimensional scaling ................................................................... 28 LOPO analysis.............................................................................................. 29 Drop core prey (DCP) analysis .................................................................... 29 1.3.6 Quantitative Fatty Acid Signature Analysis .............................................. 31 Final diet estimation ..................................................................................... 31 Quantifying QFASA model error: Diet simulations ..................................... 31 1.4 Results .............................................................................................................. 32 1.4.1 QFASA Diagnostics................................................................................... 32 Reliability of the calibration coefficients ..................................................... 32 Degree of prey confounding ......................................................................... 33 Simulations and prey-specific error ............................................................. 34 1.4.2 Diet Characterization ................................................................................. 35 1.5 Discussion ........................................................................................................ 37 1.5.1 Diet of Female Northern Elephant Seals ................................................... 37 1.5.2 Evaluating QFASA .................................................................................... 43 1.5.3 Conclusions ................................................................................................ 45 1.6 References ........................................................................................................ 47 CHAPTER 2: Spatial, Seasonal, and Interannual Diet Differences Revealed for a Deep-Diving Ocean Predator ......................................68 2.1 Abstract............................................................................................................ 68 2.2 Introduction ..................................................................................................... 69 2.3 Materials and Methods ................................................................................... 73 2.3.1 Sample Collection ...................................................................................... 73 2.3.2 Lipid Analysis and QFASA ....................................................................... 75 2.3.3 Prey Functional Groups ............................................................................. 76 2.3.4 Spatial Strategy Classification ................................................................... 77 2.3.5 Statistical Analyses .................................................................................... 77 2.4 Results .............................................................................................................. 79 iv 2.4.1 Spatial Variability in Diet .......................................................................... 79 Between-province variability: Winter-Spring .............................................. 80 Between-province variability: Summer-Fall ................................................ 81 2.4.2 Temporal Variability in Diet ...................................................................... 82 Interannual variability: Winter-Spring ........................................................ 83 Interannual variability: Summer-Fall .......................................................... 84 2.5 Discussion ........................................................................................................ 85 2.5.1 Influence of Intrinsic Physiological Constraints ........................................ 86 2.5.2 Influence of the Oxygen Minimum Zone (OMZ) ...................................... 88 2.5.3 Influence of Ocean Climate Variability ..................................................... 91 2.5.4 Conclusions ................................................................................................ 94 2.6 References ........................................................................................................ 96 CHAPTER 3: Vertical Foraging Strategies Reflect Spatiotemporal Differences in Diet for a Mesopelagic Predator ................................114 3.1 Abstract.......................................................................................................... 114 3.2 Introduction ................................................................................................... 115 3.3 Materials and Methods ................................................................................. 119 3.3.1 Elephant Seal Sampling ........................................................................... 119 3.3.2 Diet Determination................................................................................... 120 3.3.3 Diving and Movement Data Processing .................................................. 121 3.3.4 Classification of Vertical Foraging Strategies ......................................... 122 3.3.5 Individual Diet Specialization and Site Fidelity ...................................... 122 3.3.6 Statistical Analyses .................................................................................. 123 3.4 Results ............................................................................................................ 125 3.4.1 Spatial Variability in Diet: Key Prey Functional Groups ........................ 125 3.4.2 Variation in Foraging Dive Behavior ...................................................... 125 3.4.3 Spatiotemporal Variability in Vertical Foraging Strategies ..................... 126 3.4.4 Vertical