UNIVERSITY OF COPENH AGEN DEPARTMENT O F B I O L O G Y PhD thesis Julius Nielsen The Greenland shark (Somniosus microcephalus) Diet, tracking and radiocarbon age estimates reveal the world’s oldest vertebrate Academic supervisors Professor John Fleng Steffensen, Senior Scientist Rasmus Berg Hedeholm, Professor Jørgen Schou Christiansen, Professor Peter Gerald Bushnell and Associate Professor Kim Præbel Submitted: 30 November 2017 2 Table of contents 1. PREFACE ........................................................................................................................ 5 2. ACKNOWLEDGEMENTS ............................................................................................... 6 3. ENGLISH SUMMARY ..................................................................................................... 8 4. DANSK SAMMENDRAG ................................................................................................. 9 5. KALAALLISUT EQIKKAANEQ .................................................................................... 10 6. PROLOGUE .................................................................................................................. 12 7. INTRODUCTION TO THE GREENLAND SHARK ........................................................ 15 7.1 Historical interactions with humans ....................................................................................................................... 15 7.2 Taxonomy .................................................................................................................................................................. 18 7.3 Distribution ............................................................................................................................................................... 19 7.4 Morphology and sensory organs.............................................................................................................................. 21 7.5 Body size .................................................................................................................................................................... 23 7.6 Reproduction ............................................................................................................................................................. 25 7.7 Migration ................................................................................................................................................................... 28 7.8 Diet ............................................................................................................................................................................. 29 8. AGE INVESTIGATIONS ................................................................................................ 33 8.1 Age determination techniques on elasmobranchs .................................................................................................. 33 8.2 The eye lens as biogenic archive .............................................................................................................................. 35 8.3 Marine radiocarbon dating ...................................................................................................................................... 37 8.3.1 Bomb radiocarbon dating .................................................................................................................................... 38 8.3.2 Pre-bomb radiocarbon dating .............................................................................................................................. 41 9. RATIONALE, HYPOTHESIS, AIMS .............................................................................. 43 9.1 Rationale .................................................................................................................................................................... 43 3 9.2 Hypothesis ................................................................................................................................................................. 43 9.3 Aims ........................................................................................................................................................................... 43 10. SUMMARY OF RESULTS ........................................................................................... 44 10.1 Manuscript 1 (MS1) – Feeding ecology ................................................................................................................. 44 10.2 Manuscript 2 (MS2) – Tracking ............................................................................................................................ 45 10.3 Article 1 (A1) – Age ................................................................................................................................................ 46 11. DISCUSSION .............................................................................................................. 47 11.1 Rationale .................................................................................................................................................................. 47 11.1.1 The Greenland shark chronology ...................................................................................................................... 47 11.1.2 The carbon source of the eye lens nucleus Greenland shark chronology .......................................................... 49 11.1.3 Radiocarbon in the northern North Atlantic ...................................................................................................... 50 11.1.4 Conventional use of bomb radiocarbon for age validation ............................................................................... 52 11.1.5 Bomb radiocarbon dating of the Greenland shark chronology ......................................................................... 52 11.1.6 The Bayesian model on the pre-bomb portion of the Greenland shark chronology .......................................... 53 11.1.7 How to interpret calibrations ............................................................................................................................. 54 11.1.8 The challenge of reservoir age .......................................................................................................................... 54 11.2 The bomb pulse at living depth of the Greenland shark ..................................................................................... 55 11.2.1 Existing reference chronologies of dietary origin ............................................................................................. 55 11.2.2 The bomb pulse in deep sea and abyssal food webs ......................................................................................... 57 11.3 Weaknesses and potential improvements of the study ........................................................................................ 58 11.3.1 Calibration-associated weaknesses ................................................................................................................... 58 11.3.2 Future improvements ........................................................................................................................................ 59 12. CONCLUSION ............................................................................................................. 62 13. PERSPECTIVES ......................................................................................................... 63 14. REFERENCES ............................................................................................................ 65 15. APPENDIX I ................................................................................................................ 75 16. MANUSCRIPTS........................................................................................................... 76 4 1. Preface This thesis has been submitted to the PhD School of The Faculty of Science, University of Copenhagen (Denmark) to obtain the PhD degree. The main part of this work has been carried out at the Marine biological section, Department of Biology, Faculty of Science, University of Copenhagen, Denmark with Professor John Fleng Steffensen as main supervisor. Several co- supervisors have also been involved: Senior Scientist Rasmus Berg Hedeholm from the Greenland Institute of Natural Resources (Greenland), Professor Peter Bushnell from the Indiana University South Bend (USA), Associate Professor Kim Præbel and Professor Jørgen Schou Christiansen from UiT The Arctic University of Norway (Norway). The thesis consists of a general introduction to the Greenland shark and to marine radiocarbon dating - the age determination technique applied. Two unpublished manuscripts and one published article are included, as well as a discussion meticulously elaborating the theoretical rationale associated with applying radiocarbon dating on an animal living in the North Atlantic deep ocean. The manuscript on feeding ecology is to be submitted to Polar Biology and the manuscript on tracking is in preparation as tags are still deployed on sharks. The finding of great longevity of the Greenland shark was published as a report in Science, August 2016. In addition to the work presented here, I have been involved in and carried out several spin-off studies from the 310 sharks of which various data has been sampled during my PhD project. A full list of these studies (published and in preparation) is