Whiting (Merlangius merlangus) in Division 6.a (West of Scotland)

ICES Advice on fishing opportunities, catch, and effort Celtic Seas Ecoregion Published 30 June 2016 5.3.65 Whiting (Merlangius merlangus) in Division 6.a (West of Scotland) ICES stock advice ICES advises that when the MSY approach is applied, there should be zero catch in each of the years 2017 and 2018. Stock development over time The spawning-stock biomass (SSB) has been increasing since 2006 but remains very low compared to the historical estimates and is well below Blim. Fishing mortality (F) has declined continuously since around 2000 and is now very low. Recruitment is estimated to have been very low since 2002 but estimated to have increased in recent years. Figure 5.3.65.1 Whiting in Division 6.a. Observed catches and summary of stock assessment (weights in thousand tonnes). The shaded areas in the bottom panels correspond to two standard errors for estimates of mortality and SSB. Predicted values in the recruitment plot are not shaded. Stock and exploitation status Table 5.3.65.1 Maximum sustainable yield Whiting in Division 6.a. State of the stock and fishery relative to reference points. Fishing pressure Stock size 2013 2014 2015 2014 2015 2016 F MSY Appropriate MSY B trigger Below trigger Reduced Precautionary F pa, Harvested approach F B lim pa, B lim reproductive sustainably capacity Management plan F MGT - - - Not applicable SSB MGT - - - Not applicable ICES Advice 2016, Book 5 1

Published 30 June 2016 ICES Advice on fishing opportunities, catch, and effort Catch options Table 5.3.65.2 Whiting in Division 6.a. The basis for the catch options. Variable Value Source Notes F ages 2 4 (2016) 0.067 ICES (2016a) Average F (2013 2015) SSB (2017) 18 700 t ICES (2016a) Short term forecast R age1 (2016) 87.9 million ICES (2016a) Assessment model estimate R age1 (2017) 33.4 million ICES (2016a) GM (2006 2015). Catch (2016) 1004 t ICES (2016a) Short term forecast Landings (2016) 356 t ICES (2016a) Average discard rates at age of 2013 2015. Discards (2016) 648 t ICES (2016a) Average discard rates at age of 2013 2015. Table 5.3.65.3 Whiting in Division 6.a. The catch options. Weight in tonnes. Rationale Catch Wanted Unwanted F F wanted F unwanted % TAC % SSB SSB total catch* catch* Basis Total catch catch change change (2018) (2017) (2017) (2017) (2017) (2017) (2017) ** *** MSY approach 0 0 0 Zero catch 0 0 0 16 966 100 9 377 181 199 TAC 2016 15% 0.025 0.011 0.014 16 539 15 12 444 213 234 TAC 2016 0.029 0.013 0.016 16 464 0 12 510 245 269 TAC 2016 +15% 0.034 0.015 0.019 16 388 15 12 991 475 523 F 2016 0.067 0.030 0.037 15 847 123 15 Other 4083 1907 2102 F options^ lim 0.270 0.120 0.150 12 593 795 33 2799 1342 1479 F pa 0.190 0.084 0.106 13 874 530 26 1114 534 589 F MSY SSB 2017/MSY 0.075 0.034 0.042 15 709 151 16 B trigger SSB 2018=B pa=msy Btrigger * Wanted catch is used to describe fish that would be landed in the absence of the EU landing obligation. The unwanted catch refers to the component that was previously discarded. ** Wanted catch in 2016 compared with the TAC of Subarea 6, whereas the stock area is only Division 6.a. *** SSB 2018 relative to SSB 2017. ^ The B pa and MSY B trigger option was left blank because SSB 2018=B pa=msy Btrigger cannot be achieved in 2018 even with zero catch advice. Basis of the advice Table 5.3.65.4 Whiting in Division 6.a. The basis of the advice. Advice basis MSY approach Management plan There is no management plan for whiting in this area. Quality of the assessment The improved optimization of the assessment model this year resulted in a downward revision of the stock biomass and an upward revision of F when compared to the previous assessment. The assessment indicates an increasing mismatch between the survey and the fishery catchabilities. This is most likely linked to changes in fishery selectivity due to changes in effort for different métiers and the introduction of various technical measures in 6.a. These are not explicitly taken into account in the assessment model. The majority of catches have been discarded in recent years. Discard information is imprecise compared to landings data due to low sampling levels. The mean weights-at-age in the catch have been quite variable in recent years because of low and patchy sampling. This implies that the catch information of recent years in the assessment is less certain. The inclusion of the two new Scottish survey time-series increased the precision of the assessment of this stock (ICES, 2015). 2 ICES Advice 2016, Book 5

ICES Advice on fishing opportunities, catch, and effort Published 30 June 2016 Figure 5.3.65.2 Whiting in Division 6.a. Historical assessment results (final-year recruitment estimates included). Issues relevant for the advice The increase in mesh size from 100 mm to 120 mm, under the emergency measures since 2010 and the introduction of large square mesh panels in the Nephrops fishery, are likely to have contributed to the observed reductions in fishing mortality. Given the continued high discards and low TAC this stock could become a major choke species for the 6.a Nephrops fishery in the context of the landing obligation. Reference points Table 5.3.65.5 Whiting in Division 6.a. Reference points, values, and their technical basis. Framework Reference point Value Technical basis Source MSY MSY B trigger 44 600 t B pa ICES (2016a) approach F MSY 0.18 F MSY upper precautionary with B trigger(=b pa) ICES (2016a) B lim 31 900 t B lim = SSB value at the change point in the segmented regression stock recruit function. ICES (2016a) Bpa=Blim*exp(1.645σ) where σ=0.20. The value of the estimated SSB that ensures that the true SSB has less than 5% B pa 44 600 t ICES (2016a) probability of being below Blim, taking into account the Precautionary uncertainty of assessments. approach The F that gives a 50% probability of falling below Blim in the F lim 0.27 ICES (2016a) long term. Fpa=Flim*exp(-1.645σ) where σ=0.20, The value of the F pa 0.19 estimated F that ensures that the true F has less than 5% probability of being above Flim. ICES (2016a) Management plan SSB MGT Not applicable. Not applicable. F MGT ICES Advice 2016, Book 5 3

Published 30 June 2016 ICES Advice on fishing opportunities, catch, and effort Basis of the assessment Table 5.3.65.6 Whiting in Division 6.a. The basis of the assessment. ICES stock data category 1 (ICES, 2016d) Assessment type Age-based analytic assessment (TSA) that uses catches in the model and in the forecast. Commercial landings, estimated discards, age composition of catches; five survey indices (ScoGFS- Input data WIBTS-Q1, ScoGFS-WIBTS-Q4, IGFS-WIBTS-Q4, UKS-WIBTS-Q1 and UKS-WIBTS-Q4); fixed maturity data from surveys; natural mortalities estimated from mean weight-at-age (Lorenzen s model (Lorenzen, 1996) using mean weight data from market sampling and discard observations). Discards and bycatch Included in the assessment, data series from the main fleets (covering 95% of the landings). Indicators None Other information The stock was benchmarked in 2012 (WKROUND; ICES, 2012) and in 2015 (IBPWSRound; ICES, 2015). Working group Working Group for the Celtic Seas Ecoregion (WGCSE) Information from stakeholders Industry notes that the discard information is imprecise. Since 2014, effort has been made to improve coverage by the Scottish industry/science observer sampling scheme in Subarea 6. The sampling coverage now is more likely to reflect fishing patterns. In 2015, the industry group GITAG (Gear Innovation and Technology Advisory Group) was established to stimulate innovation in the development of fishing gear technology aimed at trialing and providing new process and techniques. These will assist the Scottish fishing industry s transition to the operational requirements of the phasing in of the landing obligation whilst protecting economic viability. The first phase of the project focused on gear development in the Nephrops trawling sector to reduce catches, particularly of juveniles. Indications from the first three sets of trials conducted by GITAG provide encouragement that practical solutions will greatly improve the reduction of juvenile whiting catches. 4 ICES Advice 2016, Book 5

ICES Advice on fishing opportunities, catch, and effort Published 30 June 2016 History of advice, catch, and management Table 5.3.65.7 Whiting in Division 6.a. History of ICES advice, the agreed TAC, ICES estimates of landings and discards. Weights in thousand tonnes. Year ICES advice / Predicted catch Official ICES Agreed TAC* Single-stock exploitation boundaries since 2004 corresp. to advice landings landings Discards^ ICES catch 1987 No increase in F 15.0 16.4 12.4 11.5 6.9 18.4 1988 No increase in F; TAC 15.0 16.4 11.9 11.4 11.8 23.1 1989 No increase in F; TAC 13.0 16.4 7.7 7.5 4.1 11.6 1990 No increase in F; TAC 11.0 11.0 6.0 5.6 4.4 10.0 1991 70% of effort (89) - 9.0 6.9 6.7 5.3 12.0 1992 70% of effort (89) - 7.5 6.0 6.0 9.4 15.4 1993 70% of effort (89) - 8.7 6.8 6.9 8.5 15.4 1994 30% reduction in effort - 6.8 5.8 5.9 8.9 14.8 1995 Significant reduction in effort - 6.8 6.3 6.1 7.6 13.7 1996 Significant reduction in effort - 10.0 6.6 7.2 6.9 14.1 1997 Significant reduction in effort - 13.0 6.2 6.3 4.9 11.2 1998 No increase in F 6.5 9.0 4.7 4.6 5.8 10.5 1999 Reduce F below F pa 4.3 6.3 4.7 4.6 3.1 7.7 2000 Reduce F below F pa < 4.3 4.3 3.2 3.0 6.7 9.7 2001 Reduce F below F pa < 4.2 4.0 2.5 2.4 2.4 4.9 2002 SSB >B pa in the short term < 2.0 3.5 1.7 1.7 2.1 3.8 2003 No cod catches - 2.0 1.3 1.3 1.6 2.9 2004 SSB >B pa in the short term ** < 2.1*** 1.6 0.8 0.8 2.6 3.4 2005 Exploitation not allowed to increase < 1.6 1.6 0.29 0.3 0.9 1.2 2006 Lowest possible level 0 1.36 0.38 0.4 0.9 1.3 2007 Lowest possible level 0 1.02 0.48 0.5 0.3 0.8 2008 Lowest possible level 0 0.765 0.44 0.4 0.2 0.4 2009 Same advice as last year 0 0.574 0.49 0.5 0.4 0.9 2010 Same advice as last year 0 0.431 0.35 0.3 0.9 1.2 2011 See scenarios - 0.323 0.23 0.2 0.3 0.6 2012 Reduce catches - 0.307* 0.30 0.3 0.7 1.0 2013 Lowest possible catch, improve selectivity 0 0.292* 0.21 0.2 1.0 1.2 2014 Lowest possible catch, improve selectivity 0 0.292* 0.17 0.2 0.6 0.8 2015 Lowest possible catch 0 0.263* 0.22 0.2 0.8 1.0 2016 Precautionary approach (minimize all catches) 0 0.213* 2017 MSY approach 0 2018 MSY approach 0 * TAC is set for divisions 6.a and 6.b combined. ** TAC is set for Division 5.b and subareas 6, 12, and 14. *** Single-stock boundary and the exploitation of this stock should be conducted in the context of mixed fisheries, protecting stocks outside safe biological limits. ^ Discards estimated for ages 1+ History of catch and landings Table 5.3.65.8 Whiting in Division 6.a. Catch distribution by fleet in 2015 as estimated by ICES. Catch (2015) Landings Discards* Finfish directed otter Nephrops directed Finfish directed Nephrops directed otter Other gear trawl otter trawl otter trawl trawl 1620 tonnes 87% 1% 12% 12% 77% 220 tonnes 1400 tonnes * All discards, including the 0-group (note that discard estimates in Tables 5.3.65.7 and 5.3.65.10 are for 1+ discards). ICES Advice 2016, Book 5 5

Published 30 June 2016 ICES Advice on fishing opportunities, catch, and effort Table 5.3.65.9 Whiting in Division 6.a. History of official landings by countries participating in the fishery. Year Belgium Denmark Faroe Islands France Germany Ireland Netherlands Norway Spain UK (E W & NI) UK (Scot.) UK (total) Total official landings 1989 1 1-199 <0.5 1315 - - - 44 6109 7669 1990 - <0.5-180 <0.5 977 - - - 50 4819 6026 1991 <0.5 3-352 <0.5 1200 - - - 218 5135 6908 1992-1 - 105 1 1377 - - - 196 4330 6010 1993 <0.5 1-149 1 1192 - - - 184 5224 6751 1994 <0.5 <0.5-191 <0.5 1213 - - - 233 4149 5786 1995 <0.5 <0.5-362 - 1448 - - 1 204 4263 6278 1996 - <0.5-202 <0.5 1182 - - - 237 5021 6642 1997 1 <0.5-108 - 977 - - 1 453 4638 6178 1998 1 - - 82-952 - - 2 251 3369 4657 1999 <0.5 - - 300 <0.5 1121 - - <0.5 210 3046 4677 2000 - - - 48-793 - - - 104 2258 3203 2001 - - - 52-764 - - 2 71 1654 2543 2002 - - - 21-577 - - - 73 1064 1735 2003 - <0.5-11 - 568 - - - 35 751 1365 2004 <0.5 <0.5-6 - 356 - - - 13 444 819 2005 - - - 9-172 - - - 5 103 289 2006 - - - 7 <0.5 196 - - - 2 178 383 2007 - - <0.5 6 1 56 - - - 1 424 488 2008 - - <0.5 1-69 - - - - - 370 441 2009 - - - 1-125 - 2 - - - 354 482 2010 - - <0.5 3-99 - - - - - 247 349 2011 - - 1 + - 149 - - - - - 80 230 2012 - - 1 + - 96 - - - - - 204 301 2013 - - - 1-97 - - - - - 116 214 2014 - - - 1-97 - - - - - 83 181 2015* - - - <0.5-88 11 - - - - 122 221 * Preliminary. 6 ICES Advice 2016, Book 5

ICES Advice on fishing opportunities, catch, and effort Published 30 June 2016 Summary of the assessment Table 5.3.65.10 Whiting in Division 6.a. Assessment summary with weights (in tonnes). Year Recruitment Age 1 thousands High Low SSB tonnes High Low Landings tonnes Discards tonnes Mean F Ages 2-4 1981 199 412 239 077 159 746 134 808 149 789 119 827 12 194 2132 0.224 0.263 0.184 1982 165 965 200 628 131 303 92 228 102 103 82 354 13 880 5485 0.252 0.297 0.207 1983 197 470 235 533 159 407 63 447 70 522 56 373 15 962 6294 0.417 0.487 0.348 1984 327 360 379 822 274 899 46 310 52 022 40 598 16 459 4017 0.535 0.622 0.448 1985 311 455 358 800 264 110 42 559 47 887 37 231 12 879 4840 0.62 0.715 0.525 1986 292 148 334 716 249 580 38 534 43 396 33 671 8458 2669 0.484 0.562 0.405 1987 405 448 471 977 338 920 41 043 45 822 36 263 11 542 11 918 0.583 0.673 0.492 1988 107 793 130 312 85 274 41 707 46 704 36 711 11 349 8132 0.681 0.785 0.576 1989 327 864 371 492 284 236 22 949 26 250 19 647 7523 5876 0.606 0.705 0.508 1990 175 330 212 390 138 269 33 896 38 002 29 790 5642 4530 0.437 0.515 0.359 1991 246 749 293 588 199 909 27 710 31 407 24 014 6658 4883 0.443 0.523 0.363 1992 338 629 396 708 280 551 30 931 35 205 26 657 6005 9249 0.428 0.508 0.347 1993 269 148 317 464 220 833 43 908 50 028 37 787 6872 4759 0.452 0.543 0.361 1994 284 536 337 890 231 183 38 773 44 927 32 620 5901 3455 0.403 0.488 0.318 1995 303 509 353 757 253 261 39 057 46 298 31 816 6078 5771 0.451 0.559 0.344 1996 191 840 232 964 150 715 42 712 50 265 35 159 7158 7940 0.563 0.704 0.421 1997 177 171 224 276 130 066 34 061 40 565 27 556 6290 5251 0.623 0.78 0.467 1998 233 525 300 114 166 937 24 199 30 361 18 037 4627 9216 0.699 0.858 0.539 1999 168 645 225 314 111 977 21 983 28 832 15 135 4613 3975 0.845 1.02 0.67 2000 261 927 345 314 178 539 16 493 22 509 10 477 3011 13 285 0.818 0.988 0.649 2001 109 882 144 075 75 689 18 586 24 851 12 321 2439 4263 0.735 0.894 0.576 2002 42 134 60 365 23 902 13 282 17 762 8802 1767 2851 0.534 0.661 0.408 2003 64 743 88 440 41 046 8163 11 038 5289 1355 719 0.565 0.701 0.428 2004 40 492 55 431 25 552 5905 8068 3742 811 2159 0.597 0.763 0.431 2005 23 850 30 614 17 085 3841 5019 2662 341 629 0.493 0.652 0.333 2006 27 953 32 974 22 932 3491 3984 2999 380 946 0.412 0.494 0.33 2007 14 785 18 252 11 318 3454 3867 3041 427 317 0.323 0.393 0.253 2008 16 907 20 087 13 728 3050 3483 2616 445 314 0.355 0.428 0.282 2009 25 932 30 033 21 832 3499 4045 2953 488 419 0.3 0.365 0.236 2010 64 382 76 297 52 468 2889 3335 2443 307 893 0.218 0.267 0.169 2011 20 197 23 901 16 493 6235 7312 5159 230 339 0.132 0.164 0.1 2012 44 057 56 040 32 073 6158 7257 5058 313 727 0.114 0.145 0.082 2013 23 949 31 166 16 732 7558 9234 5883 222 951 0.082 0.107 0.057 2014 65 998 90 357 41 639 7649 9494 5805 184 583 0.061 0.081 0.041 2015 105 780 133 982 77 577 10 020 13 027 7012 227 835 0.057 0.078 0.037 2016 87 905* 146 730 29 080 16 247 20 599 11 896 Average 160 135 194 469 125 802 27 704 32 091 23 317 5230 4018 0.444 0.537 0.351 * Model estimate. High Low ICES Advice 2016, Book 5 7

Published 30 June 2016 ICES Advice on fishing opportunities, catch, and effort Sources and references ICES. 2012. Report of the Benchmark Workshop on Western Waters Roundfish (WKROUND), 22 29 February 2012, Aberdeen, UK. ICES CM 2012/ACOM:49. 283 pp. ICES. 2015. Report of the Inter-Benchmark Protocol of West of Scotland Roundfish (IBPWSRound), February April 2015. By correspondence. ICES CM 2015/ACOM:37. 99 pp. ICES. 2016a. Report of the Working Group for the Celtic Seas Ecoregion (WGCSE), 04 13 May 2016, ICES Headquarters, Copenhagen, Denmark. ICES CM 2016/ACOM:13. ICES. 2016d. General context of ICES advice. In Report of the ICES Advisory Committee, 2016. ICES Advice 2016, Book 1, Section 1.2. ICES. 2016b. EU request to ICES to provide FMSY ranges for selected stocks in ICES subareas 5 to 10. In Report of the ICES Advisory Committee, 2016. ICES Advice 2016, Book 5, Section 5.2.3.1. ICES. 2016c. Report of the Workshop to consider FMSY ranges for stocks in ICES categories 1 and 2 in Western Waters (WKMSYREF4), 13 16 October 2015, Brest, France. ICES CM 2015/ACOM:58. 187 pp Lorenzen, K. 1996. The relationship between body weight and natural mortality in juvenile and adult fish: a comparison of natural ecosystems and aquaculture. Journal of Fish Biology, 49(4): 627 642. 8 ICES Advice 2016, Book 5