A Comprehensive Study of Fish Stocks and Fisheries of Cowichan Lake Tkpics 2012 Tracy Michalski Fish Research Biologist Research Section – West Coast Region Ministry of Forests, Lands and Natural Resource Operations 103-2100 Labieux Road, Nanaimo, BC V9T 6E9 October 5, 2016 Contents Acknowledgments .......................................................................................................................4 1.0 Introduction ......................................................................................................................5 1.1 The Cowichan Lake Operational Management Plan – Background ...................................5 1.2 Lake Characteristics ..........................................................................................................6 1.3 Fisheries ............................................................................................................................8 1.4 Management Issues ..........................................................................................................9 1.5 Specific Objectives ..........................................................................................................10 2.0 Methods ..............................................................................................................................11 2.1 Review of Historical Fisheries and Stock Data ................................................................. 11 2.2 Angler Counts and Interviews ..........................................................................................11 Catch and Harvest .............................................................................................................12 2.3 Angler Preference Surveys ..............................................................................................13 2.4 Gillnet and Trap Net Sampling .........................................................................................13 2.5 Spawning Surveys ...........................................................................................................14 2.6 Electrofishing Surveys .....................................................................................................15 2.7 Fish Aging .......................................................................................................................15 2.8 Kokanee Surveys ............................................................................................................15 2.9 Determining Fisheries Objectives and Management Strategies .......................................16 3.0 Results ................................................................................................................................16 3.1 Angler Effort ....................................................................................................................16 3.2 Catch and Harvest ...........................................................................................................17 3.3 Size of Angler-Caught and Harvested Fish ......................................................................18 3.4 Angler Preferences ..........................................................................................................19 3.5 Cowichan Lake Derbies ...................................................................................................21 Angler Effort ....................................................................................................................... 21 Creel Survey and Weigh-In at the 2012 Frost Bite Derby ...................................................22 Derby Catch ....................................................................................................................... 22 Size of Derby-Caught Cutthroat Trout ................................................................................23 3.6 Stock Assessment ...........................................................................................................26 Relative Abundance ...........................................................................................................26 Length and Weight .............................................................................................................28 Length Frequency Analysis ................................................................................................28 Gillnetting ...........................................................................................................................31 Net Traps ...........................................................................................................................32 Condition Factor ................................................................................................................33 Length Weight Relationships .............................................................................................34 Age and Growth .................................................................................................................35 Immature Fish ....................................................................................................................38 Ageing – Anterior Scale Radius .........................................................................................39 Spawning ...........................................................................................................................41 Juveniles Egg Incubation, Fry Emergence and Juvenile Recruitment ................................45 Estimates of Juvenile Population .......................................................................................46 3.7 Kokanee Salmon .............................................................................................................48 Population Abundance and Status .....................................................................................51 3.8 Cowichan Lake Lamprey ................................................................................................. 52 4.0 Discussion...........................................................................................................................53 4.1 Fisheries Management ....................................................................................................53 4.2 Stock and Fishery Monitoring .......................................................................................... 56 3. Monitor the Cowichan Lake derby fishery ................................................................... 57 Fish Stocks and Fisheries of Cowichan Lake October, 2016 4.3 Recommendations for additional study and assessment to support science and management of trout populations in Cowichan Lake ..............................................................57 5.0 References .........................................................................................................................61 Appendix 1. ...............................................................................................................................68 Cowichan Lake Creel Survey Calendars 2010, 2011 .............................................................68 Appendix 2. ...............................................................................................................................69 Cowichan Lake Creel Survey Instructions .............................................................................69 Appendix 3. ...............................................................................................................................70 Angler Effort and Total Catch Reported in Creel Surveys at Cowichan Lake July, 2009 – June, 2011 ......................................................................................................................................70 Appendix 4 ................................................................................................................................74 Cowichan Lake Derby Schedule 2009 - 2012 ........................................................................74 Appendix 5. ...............................................................................................................................75 Gillnet Catch Summary for August 2009 and August 2011. ....................................................75 Appendix 6. ...............................................................................................................................76 Terms of Reference for the Cowichan Lake Fisheries Subcommittee – November, 2011 ....... 76 Appendix 7. ...............................................................................................................................79 Size of Cutthroat and Rainbow Trout in Vancouver Island Large Lakes ................................. 79 Appendix 8. ...............................................................................................................................80 Length-at-Age of Rainbow Trout and Dolly Varden Char Captured in Vancouver Island Large Lakes1948 – 2010. ................................................................................................................80 Appendix 9 ................................................................................................................................81 Stock and Fisheries Monitoring for Cowichan Lake ...............................................................81 3 Fish Stocks and Fisheries of Cowichan Lake October, 2016 Acknowledgments This project was made possible because of the generous volunteer support