ICES WKSAND 2016 REPORT ICES ADVISORY COMMITTEE ICES CM 2016/ACOM:33 REF. ACOM: Report of the Benchmark Workshop on Sandeel (WKSand 2016) 31 October – 4 November 2016 Bergen, Norway International Council for the Exploration of the Sea Conseil International pour l’Exploration de la Mer H. C. Andersens Boulevard 44–46 DK-1553 Copenhagen V Denmark Telephone (+45) 33 38 67 00 Telefax (+45) 33 93 42 15 www.ices.dk [email protected] Recommended format for purposes of citation: ICES. 2017. Report of the Benchmark on Sandeel (WKSand 2016), 31 October - 4 No- vember 2016, Bergen, Norway. ICES CM 2016/ACOM:33. 319 pp. For permission to reproduce material from this publication, please apply to the Gen- eral Secretary. The document is a report of an Expert Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the views of the Council. © 2017 International Council for the Exploration of the Sea Contents Executive summary ................................................................................................................ 1 1 Description of the Benchmark Process ...................................................................... 2 1.1 Stock ID and sub-stock structure ........................................................................ 2 1.1.1 Stock delineation ...................................................................................... 2 1.1.2 Demographic comparisons among stock assessment areas ............. 11 1.1.3 Comparison of stock trends .................................................................. 11 1.2 Issue lists .............................................................................................................. 12 1.3 Scorecard on data quality .................................................................................. 21 1.4 Multispecies and mixed fisheries issues .......................................................... 23 1.5 Ecosystem drivers ............................................................................................... 23 1.5.1 Bottom-up effects on sandeel ............................................................... 23 1.5.2 Top-down effects on sandeel ................................................................ 25 1.5.3 Distribution of sandeel predators ........................................................ 28 1.5.4 Spatial patterns in sandeel size and condition ................................... 33 1.5.5 Implications for ecosystem-based management ................................ 34 1.5.6 North East UK Closure ......................................................................... 36 1.5.7 The Norwegian spatial management of sandeel in the North Sea ................................................................................................ 39 1.6 Catch – quality, misreporting, discards ........................................................... 40 1.7 Surveys ................................................................................................................. 45 1.7.1 Dredge surveys ...................................................................................... 45 1.7.2 Acoustic survey ...................................................................................... 47 1.8 Maturity ............................................................................................................... 63 1.8.1 Estimates of main mortality sources and sensitivity of the estimated mortalities to assumptions on overlap with mackerel .................................................................................................. 63 1.9 Changes in SMS estimates of M in different WGSAM key runs .................. 71 1.10 Natural mortalities modified for inclusion in assessment ............................ 72 1.11 References ............................................................................................................ 74 1.12 Weight at age ....................................................................................................... 74 1.13 Weight at age ....................................................................................................... 74 1.14 Commercial data ................................................................................................. 74 1.14.1 Age composition and mean individual weight ................................. 74 1.14.2 Effort time series .................................................................................... 82 1.14.3 Input data ................................................................................................ 83 1.14.4 Standardising effort with respect to vessel size ................................. 83 1.14.5 Evidence of technical creep .................................................................. 83 1.14.6 Estimating b ............................................................................................ 85 1.14.7 Results ..................................................................................................... 87 1.14.8 References ............................................................................................... 89 1.14.9 Real time monitoring ............................................................................. 90 1.14.10 Overview of assessment setting decisions ..................................... 94 1.15 Proposed assessment models ............................................................................ 95 1.15.1 SMS-Effort ............................................................................................... 95 1.15.2 SESAM ..................................................................................................... 99 2 Stock (SA1r) ................................................................................................................ 100 Sandeel (Ammodytes spp.) in divisions 4.b and 4.c, Sandeel Area 1r (central and southern North Sea, Dogger Bank); ICES Statistical Rectangles 31-33 E9-F4; 33 F5; 34-37 E9-F6; 38-40 F0-F5; 41 F4-F5. ............ 100 2.1 Ecosystem drivers ............................................................................................. 100 2.2 Stock Assessment .............................................................................................. 100 2.2.1 Catch – quality, misreporting, discards ............................................ 100 2.2.2 Surveys .................................................................................................. 102 2.2.3 Maturity ................................................................................................ 103 2.2.4 Natural mortality ................................................................................. 104 2.2.5 Weight at age ........................................................................................ 105 2.2.6 Commercial data .................................................................................. 107 2.2.7 Assessment model (primary and exploratory) ................................ 110 2.2.8 Final assessment ................................................................................... 121 2.2.9 Historic Stock Trends .......................................................................... 125 2.3 Short term projections ...................................................................................... 125 2.4 Appropriate Reference Points (MSY) ............................................................. 125 3 Stock SA 2r .................................................................................................................. 126 3.1 Ecosystem drivers ............................................................................................. 126 3.2 Stock Assessment .............................................................................................. 126 3.2.1 Surveys .................................................................................................. 127 3.2.2 Maturity ................................................................................................ 129 3.2.3 Natural mortality ................................................................................. 129 3.2.4 Weight at age ........................................................................................ 129 3.2.5 Commercial data .................................................................................. 131 3.2.6 Assessment model ............................................................................... 133 3.2.7 Final assessment ................................................................................... 143 3.2.8 Historic Stock Trends .......................................................................... 147 3.3 Short term projections ...................................................................................... 147 3.4 Appropriate Reference Points (MSY) ............................................................. 147 Sandeel Area 3r .......................................................................................................... 148 4 148 4.1 Ecosystem drivers ............................................................................................. 148 4.2 Stock Assessment .............................................................................................. 148 4.2.1 Catch – quality, misreporting, discards ............................................ 148 4.2.2 Surveys .................................................................................................. 149 4.2.3