Estimating Recreational Clam and Oyster Harvest in Puget Sound (Bivalve Regions 1, 5, 6, 7 and 8)
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STATE OF WASHINGTON May 2007 Estimating Recreational Clam and Oyster Harvest in Puget Sound (Bivalve Regions 1, 5, 6, 7 and 8) by Are Strom and Alex Bradbury Washington Department of FISH AND WILDLIFE Fish Program Fish Management Division FPT-07-07 Estimating Recreational Clam and Oyster Harvest in Puget Sound (Bivalve Regions 1, 5, 6, 7 and 8) by Are Strom and Alex Bradbury May 2007 Acknowledgements We would like to thank Robert Conrad, Quantitative Services Manager for the Northwest Indian Fisheries Commission (NWIFC) for statistical advice throughout this project, and for reviewing preliminary drafts. Jennifer Cahalan, WDFW Research Scientist, provided valuable historical context on datasets used in the analyses and cheerfully answered innumerable questions on programming and statistical methods. We thank Melinda McKinley (WDFW) for accurately compiling, organizing and proofing the bulk of egress and creel data used in this study. Karla Weiss, Jennifer Whitney and Debbra Bacon (WDFW) provided additional help in compiling and error checking datasets. Brad Sele and Camille Speck provided reviews of earlier drafts. Camille also supplied detailed information on egress survey methodologies and potential sources of error. We thank David Bramwell (WDFW) for editing and producing the final manuscript. Finally, we wish to thank the many WDFW biologists and technicians who collected the egress and creel survey data. Table of Contents List of Figures...............................................................................................................................iv List of Tables .............................................................................................................................. vii Introduction....................................................................................................................................1 Part I: Current Harvest Estimation Methods..................................................................................3 General Sampling Design ..........................................................................................................3 Creel Surveys.............................................................................................................................5 Aerial Surveys............................................................................................................................6 Low Tide Counts........................................................................................................................8 Effort Expansion Factors (Egress Ratios)..................................................................................8 Plus Tide Effort Estimates .......................................................................................................12 Winter Effort Estimates ...........................................................................................................12 Estimation of Total Effort on a Beach .....................................................................................13 Step 1: Estimation of daily (all-day) effort on a sample day...............................................13 Step 2: Estimation of mean daily effort within a tide-day stratum......................................14 Step 3: Estimation of total season-long effort within a tide-day stratum ............................15 Step 4: Estimation of total effort on a beach (all strata) ......................................................15 Step 5: Estimation of a 95% confidence interval on the estimation of total effort..............16 Step 6: Addition of plus-tide and winter effort estimates....................................................16 Estimation of Within-Stratum Harvest on a Beach..................................................................17 Estimation of Total Harvest on a Beach ..................................................................................18 Part II: Analysis of the Flight Route............................................................................................19 Methods ...................................................................................................................................19 Available Data .....................................................................................................................19 Analysis ...............................................................................................................................20 Results......................................................................................................................................20 Summary of the Flight Route Analysis....................................................................................21 Part III: Analysis of Effort Stratification .....................................................................................22 Tide-Day Stratification ............................................................................................................22 Introduction..............................................................................................................................22 Methods ...................................................................................................................................23 Available Data .....................................................................................................................23 Objectives and Test Procedures...............................................................................................24 1) Analysis of Variance .......................................................................................................24 2) Cluster Analysis...............................................................................................................25 3) Monte Carlo Simulations.................................................................................................26 4) Empirical Tests................................................................................................................29 Results......................................................................................................................................29 1) Analysis of Variance .......................................................................................................29 2) Cluster Analysis...............................................................................................................30 3) Monte Carlo Simulations.................................................................................................32 4) Empirical Tests................................................................................................................33 Estimating Recreational Clam and Oyster Harvest in Puget Sound May 2007 i 5) Summary of Tide-Day Stratification Results ..................................................................34 Month-Group Stratification .....................................................................................................35 Introduction..............................................................................................................................35 Methods ...................................................................................................................................37 Available Data .....................................................................................................................37 Objectives and Test Procedures...............................................................................................38 1) Analysis of Variance .......................................................................................................38 2) Empirical Analyses..........................................................................................................39 Results......................................................................................................................................40 1) Analysis of Variance .......................................................................................................40 2) Empirical Analyses..........................................................................................................40 3) Summary of Month-Group Stratification Results ...........................................................41 Part IV: Analysis of the Effort Expansion Factor........................................................................43 Timing of Flight Counts...........................................................................................................46 Introduction..............................................................................................................................46 Methods ...................................................................................................................................47 Data......................................................................................................................................47 Analysis ...................................................................................................................................47 Results......................................................................................................................................47 1) Histograms.......................................................................................................................47 2) Boxplots...........................................................................................................................49