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On the British Columbia Geoduck Clam (Panopea Abrupta) Fishery

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On the British Columbia Geoduck Clam (Panopea Abrupta) Fishery THE POTENTIAL IMPACT OF SEA OTTERS (ENHYDRA LUTRIS) ON THE BRITISH COLUMBIA GEODUCK CLAM (PANOPEA ABRUPTA) FISHERY by Rhonda Reidy B.Sc., University of Victoria, 2000 RESEARCH PROJECT SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF RESOURCE MANAGEMENT (PLANNING) In the School of Resource and Environmental Management Report No. 513 © Rhonda Reidy 2011 SIMON FRASER UNIVERSITY Spring 2011 All rights reserved. However, in accordance with the Copyright Act of Canada, this work may be reproduced, without authorization, under the conditions for Fair Dealing. Therefore, limited reproduction of this work for the purposes of private study, research, criticism, review and news reporting is likely to be in accordance with the law, particularly if cited appropriately. APPROVAL Name: Rhonda Reidy Degree: Master of Resource Management (Planning) Title of Thesis: The potential impact of sea otters (Enhydra lutris) on the British Columbia geoduck clam (Panopea abrupta) fishery Project No. 513 Examining Committee: Chair: Erica Olson Master of Resource Management Candidate ___________________________________________ Sean Cox Senior Supervisor Associate Professor School of Resource and Environmental Management Simon Fraser University ___________________________________________ Murray Rutherford Supervisor Associate Professor School of Resource and Environmental Management Simon Fraser University Date Defended/Approved: April 20 2011 ii ABSTRACT I used fishery-independent survey data and catch curve analysis to assess the potential predation effects of sea otters (Enhydra lutris) on the British Columbia geoduck (Panopea abrupta) fishery on the west coast of Vancouver Island, by estimating geoduck total mortality rates across a gradient of sea otter abundance. Linear regression provided strong evidence of a fishing effort effect on geoduck total mortality while the main effect of otters was not significant. Harvesters, however, have increasingly reported seeing sea otters eating geoduck; thus a more balanced study design and greater sampling intensity are needed to increase the power to detect whether sea otters affect geoduck harvests. This paper concludes with an examination of the different legislative mandates of fisheries and wildlife management in Canada, and establishes that artificially limiting the sea otter’s range in B.C. would be difficult under federal law and for socio-political reasons. Keywords: Geoduck; sea otter; predation; catch curve analysis; total mortality rate; conflict. iii DEDICATION To my father Tom Reidy, who instilled in me the importance of education and whose intellectual strength and determination will inspire me always. iv ACKNOWLEDGEMENTS I would like to thank my advisor, Dr. Sean Cox, for his wisdom and understanding of my project, as well as my second committee member, Dr. Murray Rutherford, for his insight and sincere patience. Funding was provided through an NSERC Industrial Postgraduate Scholarship. Thank you to the Underwater Harvesters’ Association who contributed to my scholarship, as well as Archipelago Marine Research Ltd., for their contribution to the scholarship. Thanks to the many people at DFO who provided key logistical support, particularly Dominique Bureau who helped with designing and selecting study sites on the west coast of Vancouver Island, and Ian Murfitt and Wayne Hajas for their database work. Thanks also to Grant Dovey of West Coast Geoduck Corp. who helped me to understand the idiosyncrasies of geoduck clams. Thank you to Dr. Jane Watson and Linda Nichol who provided important clarifications about sea otters in B.C. I am particularly grateful to my colleagues in the Fisheries Science and Management Group at SFU who provided invaluable support and encouragement throughout this journey. Finally, I would like to thank Mark Malleson who, as always, provided unconditional friendship and support along the way. v TABLE OF CONTENTS Approval .......................................................................................................................................... ii Abstract .......................................................................................................................................... iii Dedication ....................................................................................................................................... iv Acknowledgements .......................................................................................................................... v Table of Contents ............................................................................................................................ vi List of Figures .............................................................................................................................. viii List of Tables ................................................................................................................................... ix Chapter 1 General Introduction .................................................................................................. 1 The geoduck clam ............................................................................................................................ 3 Geoduck habitat and biology ................................................................................................... 3 Geographic distribution of geoduck clams in B.C. ................................................................. 5 Management of geoduck fisheries ........................................................................................... 6 The sea otter ..................................................................................................................................... 9 Sea otter habitat and biology ................................................................................................... 9 Geographic distribution of sea otters in B.C. ........................................................................ 10 Status of sea otters in B.C. .................................................................................................... 11 Challenges to assessing conflict between sea otters and geoduck fisheries ................................... 12 Study objectives and project overview ........................................................................................... 14 Chapter 2 Estimating Potential Sea Otter Predation Effects on the West Coast Vancouver Island Geoduck (Panopea abrupta) Fishery ............................................................ 16 Abstract .......................................................................................................................................... 16 Introduction .................................................................................................................................... 17 Methods .......................................................................................................................................... 21 Study area .............................................................................................................................. 21 Study design and site selection .............................................................................................. 21 Geoduck survey data ............................................................................................................. 23 Sea otter survey data ............................................................................................................. 24 Number of sea otters in study sites ........................................................................................ 25 Data analysis ......................................................................................................................... 25 Analysis of geoduck densities ............................................................................................... 26 Analyses of age composition data ......................................................................................... 27 Catch curve analysis .............................................................................................................. 28 Simulation model .................................................................................................................. 30 Analysis of the effects of sea otters ....................................................................................... 31 Results ............................................................................................................................................ 33 Analysis of geoduck densities ............................................................................................... 33 Analysis of geoduck age composition ................................................................................... 34 Estimates of geoduck instantaneous total mortality rate ....................................................... 36 vi Analysis of the effects of sea otters ....................................................................................... 37 Discussion ...................................................................................................................................... 38 Estimates of geoduck total mortality ..................................................................................... 41 Future study design ..............................................................................................................
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