FRDC FINAL REPORT LINKING FISHERY-DEPENDENT AND FISHERY-INDEPENDENT ASSESSMENTS OF ABALONE FISHERIES Craig Mundy, Tim Karlov and Malcolm Haddon July 2006 FRDC Project No. 2001/074 National Library of Australia Cataloguing-in-Publication Entry Mundy, C. N. Linking fishery-dependent and fishery-independent assessments of abalone fisheries. Bibliography. ISBN 1 86295 333 3. 1. Abalone fisheries - Tasmania. 2. Abalone populations - Tasmania. 3. Fish surveys - Tasmania. 4. Fish stock assessment - Tasmania. I. Karlov, Tim. II. Haddon, Malcolm, 1953- . III. Tasmanian Aquaculture and Fisheries Institute. IV. Title. (Series : FRDC project ; no. 2001/074). 639.483209946. Published by the Marine Research Laboratories, Tasmanian Aquaculture and Fisheries Institute, University of Tasmania, Private Bag 49, Hobart, Tasmania 7001. E-mail: [email protected]. Ph. (03) 6227 7277 Fax (03) 6227 8035 The opinions expressed in this report are those of the author/s and are not necessarily those of the Tasmanian Aquaculture and Fisheries Institute. © Tasmanian Aquaculture and Fisheries Institute, University of Tasmania 2005. Copyright protects this publication. Except for purposes permitted by the Copyright Act, reproduction by whatever means is prohibited without the prior written permission of the Tasmanian Aquaculture and Fisheries Institute. FRDC FINAL REPORT LINKING FISHERY-DEPENDENT AND FISHERY- INDEPENDENT ASSESSMENTS OF ABALONE FISHERIES Craig Mundy, Tim Karlov and Malcolm Haddon July 2006 FRDC Project No. 2001/074 Tasmanian Aquaculture and Fisheries Institute Marine Research Laboratories TABLE OF CONTENTS Project Summary....................................................................................................................6 1. Background ...................................................................................................................11 2. Need................................................................................................................................12 3. Objectives ......................................................................................................................13 4. Sampling Designs and Methods for Estimating Abalone Abundance. ....................14 4.1. Fixed vs random sampling designs for Tasmanian habitats...................................14 4.1.1. Practicality of using completely random versus permanent sites...................14 4.1.2. Sampling of spatially-fixed sample units within permanent sites ..................14 4.1.3. Sampling of randomly positioned transects within permanent sites ..............16 4.2. Relative versus absolute abundance .......................................................................16 4.3. Evaluation of potential abundance estimation techniques......................................17 4.3.1. Use of electronic DiveTracker® to collect spatial data on abalone distribution and abundance. ...............................................................................................................17 4.3.2. Plotless sampling techniques. .........................................................................18 4.3.3. Variable Area Transects. ................................................................................19 4.3.3.1. Comparison of VAT and strip transect techniques.................................20 4.3.3.1.1. Methods ..................................................................................................20 4.3.3.1.2. Results from VAT simulations...............................................................22 4.3.3.1.3. Discussion of simulated VAT and strip transect techniques and recommendations........................................................................................................25 4.3.4. Timed swims...................................................................................................27 4.3.5. Tag-recapture..................................................................................................30 4.3.6. Area-based sampling ......................................................................................30 5. Radial Sampling Theory and Development of Algorithms for Representative Sampling................................................................................................................................32 5.1. The Victorian Radial Transect Protocol .................................................................32 5.2. Theory of radial techniques and complications with achieving representative sampling..............................................................................................................................34 5.2.1. Representative sampling.................................................................................34 5.2.2. Spatial biases ..................................................................................................35 5.3. Generating representative radial samples ...............................................................40 5.3.1. Background.....................................................................................................40 FRDC Final Report Page 1 5.3.2. Methods.......................................................................................................... 40 5.3.2.1. Assessment of bias in radial transect coordinate generation.................. 42 5.3.2.2. Constraining secondary spatial bias....................................................... 43 5.3.3. Results............................................................................................................ 45 5.3.3.1. Assessment of bias in radial transect coordinate generation.................. 45 5.3.3.2. Constraining secondary spatial bias....................................................... 50 5.3.4. Discussion...................................................................................................... 53 6. Field Evaluation of the Modified Radial Transect Method ..................................... 56 6.1. Comparison of surface-supply vs SCUBA for transect surveys............................ 56 6.2. Field validation of the modified radial transect method ........................................ 56 Overview of field experiments....................................................................................... 56 6.2.1. Methods.......................................................................................................... 57 6.2.1.1. Description of sites used for detailed field validation............................ 57 6.2.1.2. Field data collection............................................................................... 59 6.3. Precision and concordance of density estimates from radial and parallel transects: field validation ................................................................................................................... 62 6.3.1. Results and discussion ................................................................................... 65 6.4. Effect of radial transect length on statistical performance..................................... 68 6.4.1. Methods.......................................................................................................... 68 6.4.2. Results and Discussion .................................................................................. 69 6.5. Assessing serial autocorrelation in radial and parallel transects............................ 71 6.5.1. Methods.......................................................................................................... 71 6.5.2. Results and Discussion .................................................................................. 73 6.6. Minimal detectable population change .................................................................. 76 6.6.1. Methods.......................................................................................................... 76 6.6.2. Results and Discussion .................................................................................. 76 6.6.2.1. Survey sensitivity................................................................................... 79 6.6.2.2. Increasing sensitivity.............................................................................. 81 6.6.2.3. Site size .................................................................................................. 81 6.6.2.4. Replication ............................................................................................. 82 6.6.2.5. Time series ............................................................................................. 83 6.6.2.6. Unidirectional vs bidirectional Analyses ............................................... 83 6.6.2.7. Adjusting the levels of α and β.............................................................. 84 6.6.3. Other applications of survey results............................................................... 84 6.7. Optimal sampling parameters and cost-benefit analysis........................................ 85 6.7.1. Analysis of variance: transect length ............................................................. 86 6.7.2. Optimising survey parameters ....................................................................... 86 6.7.3. Cost-variance products................................................................................... 87 6.7.4. Precision-effort Plots...................................................................................... 88 6.7.5. Results and Discussion .................................................................................