TEMPERATURE PREFERENCE, AEROBIC SCOPE AND UPPER THERMAL TOLERANCE IN SYMPATRIC JUVENILE CHINOOK SALMON (ONCORHYNCHUS TSHAWYTSCHA) AND COHO SALMON (O. KISUTCH) by Hannah Sungaila B.Sc., University of British Columbia, 2009 THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN NATURAL RESOURCES AND ENVIRONMENTAL STUDIES (BIOLOGY) UNIVERSITY OF NORTHERN BRITISH COLUMBIA November 2018 © Hannah Sungaila, 2018 ABSTRACT Populations of Pacific salmon (Oncorhynchus spp.) are locally adapted to environmental conditions, with temperature being the most important abiotic factor. Wild Chinook salmon (O. tshawytscha) and coho salmon (O. kisutch) from the Horsefly River system in central British Columbia (BC) vary in adult migration timing, but often rear sympatrically as juveniles. These species provide an interesting opportunity to investigate adaptations to the environment in the juvenile life-history stage, which may differ from adaptations at the adult stage. I conducted three laboratory studies with wild-caught Horsefly River juvenile Chinook salmon and coho salmon to compare thermal preference, performance and tolerance between species. Temperature preference did not differ significantly between Chinook salmon and coho salmon. Aerobic scope (difference between maximum and routine metabolic rates) was also similar between the two species, and neither showed a distinct temperature optimum for peak physiological performance within the range of temperatures tested. Coho salmon had a significantly higher upper thermal limit compared to Chinook salmon, although the differences were small (0.26 ºC) and may not be biologically meaningful. Thus, these two populations appear to be well adapted for their current environmental conditions rather than show any tendencies to be differentially suited to selective pressures they will experience as adults. It is important to understand how different populations and life stages of salmon will adapt and persist in warming water temperatures, knowledge which has important implications for conservation and management of salmon stocks in BC in a changing climate. ii TABLE OF CONTENTS ABSTRACT ............................................................................................................................ ii TABLE OF CONTENTS ...................................................................................................... iii LIST OF TABLES ................................................................................................................... v LIST OF FIGURES ................................................................................................................ vi ACKNOWLEDGEMENTS ................................................................................................ viii PROLOGUE ............................................................................................................................ 1 CHAPTER 1 ............................................................................................................................. 5 STREAM TEMPERATURES AND FISH CAPTURE ABSTRACT ......................................................................................................................... 6 INTRODUCTION ............................................................................................................... 7 METHODS ........................................................................................................................... 8 Study Area ......................................................................................................................... 8 Temperature Loggers ......................................................................................................... 9 Fish Capture and Transport ............................................................................................. 11 RESULTS ........................................................................................................................... 12 Stream Temperatures ....................................................................................................... 12 Fish Capture ..................................................................................................................... 15 DISCUSSION ..................................................................................................................... 16 CHAPTER 2 ........................................................................................................................... 19 TEMPERATURE PREFERENCE ABSTRACT ....................................................................................................................... 20 INTRODUCTION ............................................................................................................. 21 METHODS ......................................................................................................................... 23 Fish Husbandry ................................................................................................................ 23 Temperature Preference Measurements .......................................................................... 24 Data and Statistical Analysis ........................................................................................... 26 RESULTS ........................................................................................................................... 28 DISCUSSION ..................................................................................................................... 31 Temperature Preference ................................................................................................... 31 Stream Origin and Acclimation Temperature .................................................................. 32 Ecological Relevance................................ ....................................................................... 34 CHAPTER 3 ........................................................................................................................... 35 AEROBIC SCOPE ABSTRACT ....................................................................................................................... 36 INTRODUCTION ............................................................................................................. 37 METHODS ......................................................................................................................... 39 Fish Husbandry ................................................................................................................ 39 iii Metabolic Rate Measurements ........................................................................................ 39 Data and Statistical Analysis ........................................................................................... 42 RESULTS ........................................................................................................................... 45 DISCUSSION ..................................................................................................................... 51 Routine and Maximum Metabolic Rates ......................................................................... 51 Aerobic Scope .................................................................................................................. 53 Fish Size .......................................................................................................................... 55 Acclimation Temperature ................................................................................................ 57 Ecological Relevance................................ ....................................................................... 58 CHAPTER 4 ........................................................................................................................... 61 UPPER THERMAL TOLERANCE ABSTRACT ....................................................................................................................... 62 INTRODUCTION ............................................................................................................. 63 METHODS ......................................................................................................................... 65 Fish Husbandry ................................................................................................................ 65 Critical Thermal Maxima Measurements ........................................................................ 65 Data and Statistical Analysis ........................................................................................... 67 RESULTS ........................................................................................................................... 68 DISCUSSION ..................................................................................................................... 71 Critical Thermal Maximum ............................................................................................. 71 Stream Origin and Acclimation Temperature .................................................................. 73 Fish Size .......................................................................................................................... 75 Ecological Relevance................................ ....................................................................... 75 EPILOGUE ...........................................................................................................................