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ICES WGNSSK REPORT 2013 403
7 Plaice in Skagerrak (IIIaN)
Significant changes have been provided to the assessment of this stock in 2012. Before then, ICES presented analyses for the combined area IIIa (Skagerrak + Kattegat), but there hadn’t been produced a final assessment since 2005 because of notable discrep-ancies in the catch at age and tuning information.
A dedicated workshop was convened in early March 2012 (ICES WKPESTO 2012) to address these issues more specifically, following the recommendations from ICES WKFLAT 2010. WKPESTO provided an overview of the distribution and linkages between the various plaice populations in the North Sea region and adjacent areas, and concluded that the collected information on biology and fishery of plaice in IIIa and adjacent waters suggested for changes in assessment units as well as in manage-ment areas. WKPESTO considered plaice in Skagerrak (Division 20) to be closely as-sociated with plaice in the North Sea, and proposed to include this area in the North Sea plaice stock assessment, although it was also recognized that local populations are present in the area and should be monitored. WKPESTO explored also the possi-bilities for combined or disaggregated assessments of current defined stocks. In par-ticular, WKPESTO considered plaice in Kattegat (Division 21), the Belts (Div. 22) and the Sound (Div 23) as one stock unit and proposed it to be assessed as such.
Last year, WGNSSK 2012 produced both the old setup (combined assessment Skager-rak-Kattegat) and the new setups (Kattegat, 22 and 23 assessment and North Sea-Skagerrak assessment, section 18). In addition, an answer to an EU-Norway request dealing with management options for Skagerrak plaice was also produced (ICES 2012). The new setup was accepted as the basis of the 2012 advice, and the TAC for 2013 was consequently de-coupled between Kattegat and Skagerrak.
In 2013, ICES does not present the combined IIIa assessment, but only the considera-tions specific to Plaice in Skagerrak. The Plaice Kattegat-SD22-23 assessment is now part of the WGBFAS. As a consequence, this section has been largely rewritten and differs substantially from the previous year’s report.
As the methodological approach to this stock is still under ongoing development, the stock annex has not been updated this year and relates still to the old combined IIIa setup. The stock annex will be updated at the latest during the benchmark scheduled for 2015.
7.1 Ecosystem aspects
A general description of the ecosystem is given in the Stock Annex.
7.1.1 Fisheries
A general description of the fishery is given in the Stock Annex.
Technical Conservation Measures
Minimum Landing Size is 27 cm.
404 ICES WGNSSK REPORT 2013
Changes in fleet dynamics
A detailed description of the fishing activities in area IIIa is available in STECF (2012)1, although results are presented aggregated for the annex IIa-Area 3b of the North Sea cod area, i.e. including North Sea (IV), Skagerrak (IIIaN) and Eastern Channel (VIId)
In 2012, 20% of the plaice landings in Skagerrak came from Fully Documented Fisher-ies, mainly from the Danish seiners operating under that scheme.
Fisheries Science Partnerships
No Fisheries Science Partnerships are applicable for this stock, but national Danish research projects involving both DTU Aqua and Danish Fishermen Association have been ongoing since 2011, driven by the initial need to address the shortcomings of this stock assessment and thereby supporting MSC certification for the Danish plaice fisheries in area IIIa. These collaborations have then extended into some international initiatives led by the NSRAC and involving EU and Norway in order to suggest some harvest control rules that could form the basis of an interim management plan2. The 2013 ICES advice sheet for Skagerrak plaice has included considerations for this.
7.1.2 ICES Advice
Until 2011, ICES produced advice for the combined area IIIa. Given that no assess-ment was produced, ICES advice was only based on trends in recent catches.
In 2012, ICES produced for the first time a separate advice for the Skagerrak, based on the new guidelines for the Data Limited Stocks (DLS). ICES used as harvest con-trol rule an index-adjusted status quo catch. The advice was based on a comparison of the two most recent index values with the three preceding values, combined with recent catch or landings data. The index value used was the Western Skagerrak IBTS biomass index from Cardinale et al. (2011) as modified by ICES WKPESTO (2012) and ICES WGNSSK (2012). On these considerations, ICES advised that catches in Skager-rak could increase by 7% compared to the recent average catch of the last 3 years, cor-responding to catches of no more than 8400 t. ICES noted also that in the depleted Eastern Skagerrak, no directed fisheries should occur and bycatch and discards should be minimized.
7.1.3 Management
There are no explicit management objectives for this stock. However as noted above, EU and Norway are considering options for an interim management plan for plaice in Skager-rak, on the basis of the putative linkages between this stock and North Sea Plaice.
In 2011, The TAC had been decreased by 15% compared to 2010, to 9 938 t (7 950 t in Skagerrak and 1 988 t for Kattegat), following the EC Policy Paper (COM(2010) 241), This corresponded to the level of landings in 2010. (Table 7.1.4).
1 http://stecf.jrc.ec.europa.eu/documents/43805/394916/12-11_STECF+12-16+-+Evaluation+of+Fishing+Effort+Regimes+pII_JRC76738.pdf
and http://stecf.jrc.ec.europa.eu/data-reports
2 http://nsrac.org/reports/meetings-c/skwg/skagerrak-and-kattegat-working-group-16th-april-2013-copenhagen/
ICES WGNSSK REPORT 2013 405
In 2012, the TAC was rolled over to the same level as 2011. In 2013, the TAC for Skag-errak was decoupled from the TAC in Kattegat for the first time. The TAC was in-creased by 15% compared to 2012, on the basis of the increasing stock and TAC in the neighbouring North Sea.
Since 2010 the TAC uptake has been close to 100%, (Figure 7.1.1)
Effort restrictions in the EC were introduced in 2003 (annual annexes to the TAC reg-ulations) for the protection of the cod stock in North Sea, Skagerrak and Eastern Channel. In 2009, the management programme switched from a days-at-sea to a kW-day system (2009 Council Regulation (EC) N° 43/2009), in which different amounts of kW-days are allocated within each area by member state to different groups of ves-sels, depending on gear and mesh size. Effort ceilings are updated annually. Plaice in Skagerrak is primarily caught by Danish seines with >120 mm mesh size with limited by-catch of cod; however, this fishery is included in the regulated TR1 category and has been deemed to annual effort ceilings reductions.
7.2 Data available
7.2.1 Catch
The official landings reported to ICES were not distinguished between Skagerrak and Kattegat until 2011. Official statistics for Skagerrak are only available for 2012. The annual landings used by the Working Group, available since 1972, are given by coun-try in Tables 7.1.1. Denmark usually stands for more than 90% of the landings (96% in 2012).
Previously, misreporting had been considered to potentially occur in the area be-tween the North Sea and the Skagerrak, and notably in the ICES rectangle 43F8 which is shared between both areas and represents a large part of the landings (Figure 7.2.1). However, extensive checks using VMS data (for vessels >15m) and investiga-tion of departure harbour for the vessels <15m showed that no obvious pattern of misreporting could be detected, and that only minor mismatch occurred between VMS and logbooks information (ICES WGNSSK 2011, ICES WKPESTO 2012). In 2012, the fishing pattern moved slightly away from that boundary rectangle towards the more central Skagerrak.
As in previous years, InterCatch was used to raise catch-at-age information. This year, as last year, information was provided by DCF metier as specified in the data call (see section 1)
Landings at age information is available from Denmark only, and this was used to raise to international landings, all metiers together. Landings strata for which age composition was available summed up to more than 95% of all landings weight. (Figure 7.2.2). There are almost no landings from age 1 plaice, and generally poor tracking of the cohorts (Figure 7.2.3).
A discards time series for the full area IIIa from Denmark and Sweden over 2002-2011 is available, but these data have not been re-compiled yet to distinguish between Skagerrak and Kattegat (the work is planned for the 2015 benchmark).
However, 2012 discards data were worked out separately for the two areas. Inter-Catch discards raising in bulk weight was applied separately to the third largest metier (FDF Danish seine), using the discards ratio from the non-FDF seiners (12%). Missing discards data for the other metiers were raised using all available discards information except those from the Swedish Nephrops and Pandalus fisheries using
406 ICES WGNSSK REPORT 2013
sorting devices, which have very low landings and consequently relatively high dis-cards rates. Average discards age composition was applied to all unsampled strata.
2012 discards were estimated at 1025 tonnes, corresponding to a discards ratio to landings of 13.4 % (=12% ratio of discards to catches). 70% of this discards estimates come from sampled strata, and 30% from the raising to unsampled strata.
7.2.2 Weight at age
Weight at age in landings is presented in Table 7.2.2 and Figure 7.2.3.
A major issue for this stock assessment is the extreme variability of the growth pat-terns obtained from biological samples, with extreme overlap of length distributions of the main ages (ICES, 2012 and Ulrich et al., 2013). This is considered as the main cause of the lack of year class signal in the catch-at-age matrix.
7.2.3 Maturity and natural mortality
Not estimated
7.2.4 Catch, effort and research vessel data
In 2013, landings and effort data by gear were computed at the level of the ICES rec-tangle. 2011 Data for the European fleet was available from the STECF online data [http://stecf.jrc.ec.europa.eu/data-reports], on the basis of the main “cod plan catego-ries”. 2012 data from Sweden, Denmark and Germany were added in the same for-mat. (Figure 7.2.1).
Additionally, ICES (2012) and Ulrich et al. (2013) considered that the area IIIa should b split in various spatial components with potentially different stock origins (Figure 7.2.4). Since 2010, nearly all catches have been taken in the Western area, while plaice by-catches in the targeted Nephrops fishery in the Eastern area have dropped to very low levels with the increased adoption of more selective gears (Figure 7.2.5). Skager-rak landings amount to around 10% of North Sea landings.
IBTS data are available in the area IIIaN. Since 2007 the WG discussed the limited spatial coverage of the surveys with regards to main fishing grounds. The IBTS sam-pling in Skagerrak has only few hauls in the Western Skagerrak. No improvements have been brought to this yet, but the issue is still being considered.
7.3 Data analyses
7.3.1 Comments from the technical review group 2012
General comments
The recommendation to redefine the stock structure is based on extensive work by the WKPESTO which reviewed all of the available information. This yet to be ap-proved plaice stock represents a divergence from the traditional stock structure where IIIaW is not considered part of the traditional Division IIIa complex. Not hav-ing been involved in the discussions, the review group has taken the approach to re-view the documentation provided for each of the Plaice stock definitions and await the decision on which stock structure is accepted.
ICES WGNSSK REPORT 2013 407
Technical comments
The report implies that it is unlikely there will be an independent assessment for IIIaW (Skagerrak) and there is inadequate survey coverage of the area. Commercial CPUE will be used as a proxy for the western Skagerrak and IBTS for the eastern.
Suggestion to using an updated version of the spatially explicit abundance indices of adult aggregations Cardinale et al. (2011) as an alternative to the commercial LPUE. This would provide new indices for the Division IIIa sub-populations and possibly eliminate the need for commercial LPUE.
Under the new assessment the IIIaW would be lumped in with the North Sea assess-ment with increased catches leading to an increase in stock biomass. This is a scaling factor with trends very similar.
Based on the NSRAC rules the West of Skagerrak TAC could increase or be rolled over as it appears to be increasing or stable and the NS is above Btrigger and rising.
Conclusions
The RG agrees with the WG conclusions on the technical aspects of the assessment for this stock. Given the recent stock affinity review and the influence of the North Sea on the Skagerrak, an analytical assessment on a single stock in area IIIa is likely not appropriate. This partitioning represents one feasible option.
7.3.2 Catch-at-age matrix
The Landings-at-age matrix is shown on the figure 7.2.3. The matrix shows clearly a limited ability to track down the cohorts over time in the Skagerrak. Weight at age has been increasing over the decade for the main ages.
7.3.3 Tuning series
Catches trends in fishing patterns by the main gear groups across areas were com-puted (Figure 7.3.1). 2012 lpue for the main fishery (TR1 in Western Skagerrak, 81% of total landings for the stock in 2012) have remained at the recent high level. Highest CPUE used to be observed at the western entrance but in 2012, these were mainly observed in the Central area.
Trends in IBTS area different between spring and autumn (Figure 7.3.2). The autumn survey seems to show consistent high signals for some year classes, and in particular at age 3 the picks correspond to the large year classes 2007, 2004 and 2002 observed in the North Sea. The spring survey is less consistent.
However, there are usually only weak correlations between the IBTS abundance indi-ces in Eastern North Sea (area 7) and the Skagerrak (area 8) (Figure 7.3.3)
A spatially-disaggregated abundance index from IBTS Quarter 1 (modified from Cardinale et al., 2011) has been suggested by ICES WKPESTO (2012) and ICES WGNSSK (2012). This index measures the density of adult aggregation during spawning and is used as an indicator of abundance of local components outside of migration periods. In 2013, the computation of this index was redrawn and made di-rectly calculated from ICES DATRAS database (Figure 7.3.4 and Table 7.3.1).
This index is relatively noisy and based on a limited number of hauls, therefore trends have been computed using a non parametric smoother (lowess with span 0.5). This indicates a smoothed recent increase in the Western component (where nearly all catches take place) of 4% per year. Conversely, in the Eastern component the abundance shows a smoothed decreasing trend of 4% also for the recent period.
408 ICES WGNSSK REPORT 2013
7.4 Exploratory analysis
No analytical assessment is presented for this stock. However, a combined assess-ment, where Skagerrak landings are included in the North Sea catches, is performed (Figure 7.4.1). Overall, an addition of around 10% of the catches scales the assess-ment, with a 15-17% increase of the SSB estimates and a 5-10% decrease in F. The rea-son why the SSB estimate is increased relatively higher than the increase in catches is that catches in Skagerrak are mainly of larger animals compared to the North Sea, as the fishery takes place with targeted and larger meshed gears.
7.4.1 Final assessment
The WG decided not to include a final assessment
7.5 Historic Stock Trends
No historical stock trends are available from the final assessment.
7.5.1 Stock perception from the North Sea fishers survey (FNSSS)
The annual FNSSS was made available to the WG. With regards to plaice, the trends in Skagerrak (areas 8) are comparable to the ones from the Eastern North Sea. Re-cruitment is also considered “moderate” to “high” in both areas.
7.6 Recruitment estimates
Not available
7.7 Short-term forecasts
Not performed
7.8 Medium-term forecasts - none
7.9 Biological reference points
No reference points
7.10 Quality of the assessment
The sustained research activity on that stock has finally led to some major changes for this stock (Ulrich et al., 2013). Skagerrak and Kattegat are no longer considered to be from the same biological unit, and the assessment has been changed accordingly.
The approach for plaice in Skagerrak is now based on a non-standard tailored ap-proach. As the stock structure is still poorly defined in Skagerrak, the assessment now builds on survey trends (Data Limited Stock category 3) by areas defined within the subdivision IIIaN, with a combined North Sea-Skagerrak.
Further work is now ongoing, aiming at clarifying the knowledge base on stock struc-ture and growth patterns using a combination of genetics, otolith analysis and hy-drodynamic modelling, which may shed new light on the dynamics of plaice population in Skagerrak. A benchmark is scheduled for 2015.
7.11 Status of the Stock
It is not possible to provide a reliable status of the stock based on analytical assess-ment. Since 2003 where a final assessment was presented for the last time, a number of indicators tended to sustain the hypothesis that the stock was currently not ex-ploited unsustainably. Landings have been stable over a long time period, and the
ICES WGNSSK REPORT 2013 409
effort of commercial fleets has decreased. There had never been sign of impaired re-cruitment.
The landings and lpue have been high in the recent years. The spring survey indi-cates that there has not been large year classes in the recent years in Skagerrak but that the abundance is globally increasing in the Western area, while the autumn sur-vey reflect to some extent some of the large year-classes estimated in the North Sea. It is therefore hypothesed that the increased Western landings are driven to some ex-tent by the increased abundance of the North Sea stock.
7.12 Management Considerations
No analytical assessment is available for the Skagerrak alone. Therefore, detailed management options cannot be presented.
ICES approach to data-limited stocks
For data-limited stocks for which an abundance index is available (DLS category 3), ICES uses as harvest control rule an index-adjusted status quo catch. This year advice is based on an estimation of the most recent trends in survey index values, combined with recent catch or landings data. Knowledge about the exploitation status also in-fluences the advised catch.
The spatially-disaggregated abundance index presented Figure 7.3.4 is used as the basis of advice. This indicates a smoothed recent increase in the Western component (where nearly all catches take place) of 4% per year, Considering that effort has de-creased recently and that lpue of the main fisheries in 2012 have remained around the same high level as in 2011, no additional reductions to reduce exploitation rate are deemed necessary in this area.
Conversely, in the Eastern component the abundance shows a smoothed decreasing trend of 4% also for the recent period, and the component is considered depleted. Catches in the area are very low (under 1% of the 2012 catches), but the actual exploi-tation rate is uncertain due to the reduced stock status.
On these considerations, ICES advises that catches in Skagerrak could increase by 4% compared to the recent average catch of the last 3 years, corresponding to catches of no more than 9833 t in 2014 (average of landings 2010-2012 with 2012 discards rate of 12% of catches =9454 t, x 1.04=9833 tonnes). In the depleted Eastern Skagerrak, no di-rected fisheries should occur and bycatch and discards should be minimized.
Alternative options for potential interim management plans
In 2013, EU and Norway are considering options for an interim management plan for plaice in Skagerrak, on the basis of the putative linkages between this stock and North Sea Plaice.
In 2012 ICES considered that a pragmatic harvest control rule indexing changes in Skagerrak TAC to the changes in the North Sea TAC or in the SSB of the combined assessment could potentially form the basis of an interim management plan, with provisions explicitly linked to a monitoring of the dynamics in local components within Skagerrak (ICES, 2012 and Table 7.12.1). The SSB estimated from the com-bined assessment raised by 10% between 2011 and 2012 and is well above MSY Btrig-ger. The West Skagerrak survey index also shows a slightly increasing trend.
An increase in the TAC in Skagerrak indexed to the changes in TAC in the North Sea (+15%) would imply catches in 2014 to be no more than 11 880 t (TAC 2013 = 9142 t
410 ICES WGNSSK REPORT 2013
landings x 1.15 = 10 513 t landings, with 12% discard ratio to catches = 11 880 tonnes catches).
An increase indexed to the changes in the combined assessment SSB would imply catches in 2014 to be no more than 11 364 t (TAC 2013 = 9142 t landings x 1.1 = 10 056 t landings, with 12% discard rate = 11 364 tonnes catches)
This interim harvest control rule should be reconsidered after the assessment bench-mark scheduled for early 2015.
7.13 References
Cardinale, M., Bartolino, V., Llope, M., Maiorano, L., Sköld M., Hagberg., J., 2011. Historical spatial baselines in conservation and management of marine resources. Fish Fish 12, 289–298.
ICES. 2012. Report of the Workshop on the Evaluation of Plaice Stocks (WKPESTO), 28 Febru-ary - 1 March 2012, ICES Headquarters, Copenhagen. ICES CM 2012/ACOM:32. 23 pp
Ulrich et al., 2013
ICES WGNSSK REPORT 2013 411
Year Total TACICES
estimatesOfficial
statisticsICES
estimatesOfficial
statisticsICES
estimatesOfficial
statisticsICES
estimatesOfficial
statisticsICES
estimatesOfficial
statisticsICES
estimatesOfficial
statisticsICES
estimates1972 5 095 70 3 5 1681973 3 871 80 6 3 9571974 3 429 70 5 3 5041975 4 888 77 6 4 9711976 9 251 51 717 6 10 0251977 12 855 142 846 6 13 8491978 13 383 94 371 9 13 8571979 11 045 67 763 9 11 8841980 9 514 71 914 11 10 5101981 8 115 110 263 13 8 5011982 7 789 146 127 11 8 0731983 6 828 155 133 14 7 1301984 7 560 311 27 22 7 9201985 9 646 296 136 18 10 0961986 10 645 202 505 26 11 3781987 11 327 241 907 27 12 5021988 9 782 281 716 41 10 8201989 5 414 320 230 33 5 9971990 8 729 779 471 69 10 0481991 5 809 472 15 315 68 6 6791992 8 514 381 16 537 106 9 554 11.21993 9 125 287 37 326 79 9 854 11.21994 8 783 315 37 325 91 9 551 11.21995 8 468 337 48 302 224 9 379 11.21996 7 304 260 11 428 8 003 11.21997 7 306 244 14 249 7 813 11.21998 6 132 208 11 98 6 449 11.21999 6 473 233 7 336 7 049 11.22000 6 680 230 5 67 6 982 11.22001 9 045 125 61 9 231 9.42002 6 470 140 3 58 6 671 6.42003 4 847 143 8 74 1 584 6 656 10.42004 5 717 179 106 1 511 7 513 9.52005 4 515 144 116 915 5 690 7.62006 6 334 175 14 142 1 190 7 855 7.62007 5 467 159 21 100 1 659 7 406 8.52008 6 901 219 5 79 403 7 607 9.32009 5 617 92 13 60 253 6 035 9.32010 7 644 153 10 49 1 332 9 187 9.32011 7 744 179 13 185 215 6 8 342 7.92012 7 328 7 104 155 155 12 9.3 122 126 10 15 021 7.92013 9.142
Norway Netherlands
Table 7.1.1. Plaice in Skagerrak. Landings in tonnes. Working Group estimates 1972-2012, and official statistics since 2012. TAC in thousands tonnes
Denmark Sweden Germany Belgium
412 ICES WGNSSK REPORT 2013
Table 7.2.1. Plaice in Skagerrak. Landings number at age.
1 2 3 4 5 6 7 8 9 10+1984 1 809 8059 9177 3915 1760 375 73 25 231985 1 142 3816 17915 5815 1633 624 154 116 971986 1 3 2172 12185 17220 3886 509 214 107 1521987 1 16 1814 8845 16315 9804 1983 293 167 1211988 1 33 1922 10081 12460 6358 2512 803 254 1481989 1 296 2256 6024 5530 2404 1032 468 194 2161990 1 1311 6462 7785 9284 3084 888 436 319 3581991 1 851 5312 8195 4480 2810 828 268 129 1621992 1 54 1406 9159 16174 4146 932 260 89 711993 1 224 2369 9351 12579 6392 1381 309 82 431994 1 19 5087 7295 9521 7596 2129 292 91 341995 1 0 655 5404 11006 6475 4848 843 119 691996 1 863 3517 6322 4849 4609 1768 1318 137 251997 1 0 541 4647 8783 4875 2985 1332 832 1211998 1 198 4783 5307 5991 2700 685 348 210 2001999 1 0 1160 6174 7456 7234 1239 361 71 1292000 1 0 1114 7270 10566 3276 854 109 10 222001 1 1035 5422 8212 10722 4540 288 76 8 332002 1 68 1513 6294 6760 4526 1672 412 44 242003 6 2606 3271 6378 7429 3942 885 121 12 92004 0 1299 14378 2847 2169 1206 173 81 8 112005 37 2449 3876 8787 2873 1334 583 144 65 112006 0 810 11177 8397 6366 840 316 141 34 162007 143 3989 6079 6977 4130 3329 486 101 34 132008 16 1183 5786 8111 5339 2260 1413 63 57 362009 0 871 7347 6457 2715 995 207 97 0 42010 26 1365 7399 9297 2826 741 186 62 51 182011 214 3494 4503 6869 5676 1796 245 124 47 02012 165 1701 8461 5514 2898 1675 180 134 68 50
ICES WGNSSK REPORT 2013 413
Table 7.2.2. Plaice in Skagerrak. Landings weight at age.
CW 1 2 3 4 5 6 7 8 9 10+1984 0.276 0.299 0.301 0.373 0.423 0.548 0.817 1.029 1.3191985 0.212 0.294 0.309 0.351 0.434 0.55 0.759 0.872 0.9931986 0.395 0.26 0.28 0.304 0.379 0.543 0.736 0.94 1.0411987 0.205 0.245 0.266 0.285 0.358 0.525 0.728 0.911 1.1271988 0.22 0.251 0.261 0.285 0.343 0.466 0.551 0.746 1.1111989 0.216 0.24 0.274 0.315 0.372 0.465 0.639 0.703 0.8761990 0.267 0.28 0.289 0.333 0.389 0.484 0.667 0.756 1.0771991 0.27 0.26 0.248 0.27 0.361 0.49 0.577 0.653 1.0321992 0.274 0.318 0.265 0.278 0.334 0.506 0.67 0.85 0.8721993 0.229 0.25 0.266 0.291 0.338 0.456 0.581 0.669 0.8841994 0.365 0.246 0.265 0.286 0.33 0.41 0.586 0.653 0.7851995 0.297 0.296 0.286 0.325 0.366 0.498 0.726 0.7671996 0.225 0.252 0.282 0.384 0.399 0.437 0.428 0.559 1.0131997 0.248 0.266 0.291 0.335 0.408 0.458 0.441 0.4921998 0.226 0.242 0.273 0.328 0.401 0.468 0.513 0.574 0.6551999 0.277 0.294 0.287 0.292 0.33 0.357 0.661 0.5852000 0.24 0.273 0.301 0.351 0.38 0.489 0.857 0.9112001 0.257 0.282 0.292 0.322 0.306 0.423 0.604 0.876 0.6582002 0.219 0.274 0.27 0.285 0.336 0.399 0.6 0.794 1.1532003 0.217 0.238 0.254 0.271 0.292 0.297 0.4 0.45 0.647 0.832004 0.237 0.278 0.338 0.379 0.405 0.576 0.783 0.816 0.8272005 0.227 0.25 0.258 0.29 0.327 0.357 0.398 0.523 0.644 0.8232006 0.166 0.254 0.264 0.287 0.346 0.357 0.405 0.478 0.578 0.6462007 0.245 0.246 0.29 0.318 0.308 0.343 0.347 0.528 0.511 1.0162008 0.239 0.274 0.299 0.295 0.328 0.396 0.456 0.567 0.551 0.4762009 0.24 0.284 0.326 0.375 0.479 0.518 0.646 1.121 0.7582010 0.206 0.271 0.307 0.331 0.393 0.482 0.524 0.453 0.526 0.7862011 0.254 0.296 0.318 0.353 0.417 0.456 0.565 0.617 0.4872012 0.232 0.271 0.347 0.366 0.406 0.473 0.492 0.498 0.605 0.638
414 ICES WGNSSK REPORT 2013
Table 7.3.1 Plaice in Subdivision 20 (Skagerrak). Biomass indices per local component. NumObs = number of observations, avg.cpue= adult biomass indices (g/hour), sd. = standard de-viation. Lowess : lowess smoothed cpue value (span=0.5)
West Skagerrak
East Skagerrak
numObs avg.cpue sd.cpue lowess
numObs avg.cpue sd.cpue lowess
1974 4 4038 3097 2599
1974 1 2464 NA 1482 1975 4 2428 3782 2912
1975 1 2909 NA 1742
1976 9 3465 6291 3226
1976 2 1418 1597 2016 1977 5 1816 1108 3541
1977 6 3189 1472 2301
1978 6 3579 4951 3853
1978 2 2584 2837 2598 1979 8 2591 2952 4164
1979 4 2055 1300 2903
1980 8 5050 3699 4475
1980 4 1256 559 3214 1981 12 9085 11638 4791
1981 6 1736 1034 3526
1982 6 10455 11913 5123
1982 6 3023 2225 3839 1983 9 2290 1418 5487
1983 10 3521 2232 4163
1984 11 4652 3579 5837
1984 11 6366 3379 4581 1985 8 5605 5569 6159
1985 9 6781 5089 4994
1986 7 3714 2253 6448
1986 13 3622 2573 5356 1987 12 9700 6122 6706
1987 13 6438 4594 5663
1988 7 10129 9012 6938
1988 9 5591 4021 5921 1989 11 7236 7289 7122
1989 10 10243 7094 6108
1990 9 7516 7001 7231
1990 9 9788 7980 6218 1991 11 5905 3950 7258
1991 8 2692 1713 6245
1992 11 7155 4801 7222
1992 9 10123 6841 6193 1993 10 13403 10930 7127
1993 9 5414 5034 6072
1994 10 8661 6426 6986
1994 11 3704 2982 5883 1995 10 13497 15000 6809
1995 12 7376 2458 5621
1996 10 6574 6168 6623
1996 10 8240 13898 5296 1997 10 4402 3359 6460
1997 12 2886 3327 4965
1998 10 4434 2045 6316
1998 10 6078 4323 4686 1999 11 5234 3562 6167
1999 11 3268 2621 4492
2000 11 7287 4838 6031
2000 9 4300 2713 4346 2001 11 5421 2053 5951
2001 9 2814 1679 4207
2002 11 6135 4249 5991
2002 6 1731 1046 4053 2003 8 3585 2458 6175
2003 9 3167 1422 3867
2004 11 6249 4247 6475
2004 11 2621 1865 3669 2005 15 5579 3203 6894
2005 11 7907 5146 3514
2006 11 8573 11857 7273
2006 11 6028 3939 3411 2007 11 20073 19761 7637
2007 11 5193 4547 3332
2008 10 6787 4058 7999
2008 11 1880 1175 3260 2009 11 4312 3658 8366
2009 10 3224 3409 3186
2010 11 12123 7692 8740
2010 9 1709 915 3105 2011 11 10542 17779 9126
2011 7 1448 812 3015
2012 10 16005 13045 9524
2012 9 1268 901 2917 2013 11 6691 8863 9930
2013 10 6025 4844 2814
ICES WGNSSK REPORT 2013 415
Table 7.12.1. candidate harvest control rule for an interim management plan (as evaluated by IC-ES, 2012)
a) If the survey abundance is at or below the lower abundance threshold*, then advise a de-crease or no fishing.
b) If the survey abundance is above the lower abundance threshold* then: North Sea / Skagerrak combined assessment SSB
West Skagerrak Survey abundance
RISING
STABLE / FALLING
Above MSY Btrigger
RISING
Skagerrak TAC increases with same rate as NS SSB** (a
Skagerrak TAC remains at same level as previous year (b)
STABLE / FALLING
Skagerrak TAC remains at same level as previous year (c
Skagerrak TAC decreases with same rate as NS SSB ** (d)
Below MSY Btrigger
RISING
Skagerrak TAC remains at same level as previous year (e
Skagerrak TAC remains at same level as previous year (f)
STABLE / FALLING
Skagerrak TAC decreases with same rate as NS SSB ** (g
Skagerrak TAC decreases with the rate of the NS SSB ** (h)
* Lower abundance threshold to be decided. ** It could be considered to use the rate of the North Sea TAC increases/decreases ra-ther than the SSB value.
416 ICES WGNSSK REPORT 2013
0
2
4
6
8
10
12
14
16
1974 1979 1984 1989 1994 1999 2004 2009
'000 t
onne
s
Landings
0
2
4
6
8
10
12
1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
'00
0 t
on
ne
s
TAC Skagerrak
ICES landings
ICES catches
Figure 7.1.1. Plaice Skagerrak. Upper : total landings 1974-2012. Lower : Landings vs. TAC in Skagerrak, 1992-2012. Total catches 2012 added.
ICES WGNSSK REPORT 2013 417
+ +
F5 F7 F9 G1
4142434445464748
5658
605 7 9 11
+
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
+
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
+
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
++ +
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
+
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
++F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
+ +
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
+++
++
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
F5 F7 F9 G1
4142434445464748
5658
60
5 7 9 11
Figure 7.2.1. EU Landings all gears 2003-2012 (from left to right then top to bottom) all gears (STECF data). Bubble max size= 4400 tonnes.
418 ICES WGNSSK REPORT 2013
SD
N_D
EF_
>=12
0_0_
0_al
lO
TB_C
RU
_90-
119_
0_0_
all
SD
N_D
EF_
>=12
0_0_
0_al
l_FD
FO
TB_D
EF_
>=12
0_0_
0_al
lG
NS
_DE
F_12
0-21
9_0_
0_al
lTB
B_D
EF_
>=12
0_0_
0_al
lM
IS_M
IS_0
_0_0
_HC
OTB
_DE
F_>=
120_
0_0_
all_
FDF
OTB
_CR
U_9
0-11
9_0_
0_al
l_FD
FS
SC
_DE
F_>=
120_
0_0_
all_
FDF
SS
C_D
EF_
>=12
0_0_
0_al
lG
NS
_DE
F_12
0-21
9_0_
0_al
l_FD
FG
NS
_DE
F_10
0-11
9_0_
0_al
lG
NS
_DE
F_>=
220_
0_0_
all
GN
S_D
EF_
>=22
0_0_
0_al
l_FD
FO
TB_C
RU
_32-
69_0
_0_a
llM
IS_M
IS_0
_0_0
_IB
CO
TB_C
RU
_90-
119_
0_0_
all
MIS
_MIS
_0_0
_0_H
CM
IS_M
IS_0
_0_0
_HC
GTR
_DE
F_al
l_0_
0_al
lO
TB_D
EF_
>=12
0_0_
0_al
lO
TB_C
RU
_32-
69_0
_0_a
llO
TB_D
EF_
>=12
0_0_
0_al
l_FD
FO
TB_C
RU
_90-
119_
0_0_
all
GN
S_D
EF_
all_
0_0_
all
GN
S_D
EF_
all_
0_0_
all
OTB
_CR
U_7
0-89
_2_3
5_al
lM
IS_M
IS_0
_0_0
_HC
LLS
_FIF
_0_0
_0_a
llO
TB_C
RU
_32-
69_2
_22_
all
0
500
1000
1500
2000
2500ple-IIIaN LandWt
landings sampled landings unsam
DenmarkGermanyNetherlandsNorwaySweden
SD
N_D
EF_
>=12
0_0_
0_al
lO
TB_C
RU
_90-
119_
0_0_
all
SD
N_D
EF_
>=12
0_0_
0_al
l_FD
FO
TB_D
EF_
>=12
0_0_
0_al
lG
NS
_DE
F_12
0-21
9_0_
0_al
lTB
B_D
EF_
>=12
0_0_
0_al
lM
IS_M
IS_0
_0_0
_HC
OTB
_DE
F_>=
120_
0_0_
all_
FDF
OTB
_CR
U_9
0-11
9_0_
0_al
l_FD
FS
SC
_DE
F_>=
120_
0_0_
all_
FDF
SS
C_D
EF_
>=12
0_0_
0_al
lG
NS
_DE
F_12
0-21
9_0_
0_al
l_FD
FG
NS
_DE
F_10
0-11
9_0_
0_al
lG
NS
_DE
F_>=
220_
0_0_
all
GN
S_D
EF_
>=22
0_0_
0_al
l_FD
FO
TB_C
RU
_32-
69_0
_0_a
llM
IS_M
IS_0
_0_0
_IB
CO
TB_C
RU
_90-
119_
0_0_
all
MIS
_MIS
_0_0
_0_H
CM
IS_M
IS_0
_0_0
_HC
GTR
_DE
F_al
l_0_
0_al
lO
TB_D
EF_
>=12
0_0_
0_al
lO
TB_C
RU
_32-
69_0
_0_a
llO
TB_D
EF_
>=12
0_0_
0_al
l_FD
FO
TB_C
RU
_90-
119_
0_0_
all
GN
S_D
EF_
all_
0_0_
all
GN
S_D
EF_
all_
0_0_
all
OTB
_CR
U_7
0-89
_2_3
5_al
lM
IS_M
IS_0
_0_0
_HC
LLS
_FIF
_0_0
_0_a
llO
TB_C
RU
_32-
69_2
_22_
all
0
50
100
150
200
250
300ple-IIIaN DisWt
landings sampled landings unsam
DenmarkGermanyNetherlandsNorwaySweden
Figure 7.2.2. Landings and discards information as provided to InterCatch before raising.
ICES WGNSSK REPORT 2013 419
Landings at age
year
age
2
3
4
5
6
7
8
1985 1990 1995 2000 2005 2010
landings weight
year
kg
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1985 1990 1995 2000 2005 2010
Figure 7.2.3. Landings number and landings weight at age (age 2 to 8) in Skagerrak
420 ICES WGNSSK REPORT 2013
Latitude
Long
itude
56
57
58
59
8 9 10 11 12
Skagerrak West
Skagerrak East
Kattegat West Kattegat
East
Figure 7.2.4 Areas defined within ICES division IIIa. From ICES WKPESTO 2012.
2004 2006 2008 2010 2012
020
000
4000
060
000
land
ings
North SeaSkagerrak WSkagerrak E
Figure 7.2.5 Landings in Skagerrak areas and compared with the North Sea.
ICES WGNSSK REPORT 2013 421
lpue
0.00
0.02
0.04
0.06
0.08
0.10
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
G G G G G G GG
G G1
1 1
1 1
11
1
1
1
2 22 2 2 2 2 2 2 2
1_SkaW
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
0.00
00.
001
0.00
20.
003
0.00
4
G
G G
G GG
G G G
G
1
1
1
1
1
11
1
11
2
22
2 22
2
2 2 2
2_SkaE
Effo
rt50
000
1000
0020
0000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
G G G GG G G G G G
1 1
1 1 1 1 1 1
11
2 2
2
2
22 2 2
22
1_SkaW
2003 2004 2005 2006 2007 2008 2009 2010 2011 20120
2000
0400
0060
0008
0000
G G G G G G G G G G1 1 1 1 1 1 1 1 1 1
2
2 2 2
22 2
22
2
2_SkaE
Land
ings
1000
2000
3000
4000
5000
6000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
G G G G GG G
G G G1
1
1
1 1
1
1
11
1
2 2
2 2 2 2 2 22 2
1_SkaW
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
050
100
150
200
G G G G G G G G G G1 1 1 1 1 1 1 1 1 1
2
2
2
2
2 2
2
22
2
2_SkaE
Figure 7.3.1 Trends in Landings, effort and lpue by gear and Skagerrak area. G=Gillnets fishery, 1 = TR1 (otter trawls and seines with >100 mesh size), 2= TR2 (otter trawls and seines with 70-99 mesh size).
422 ICES WGNSSK REPORT 2013
Age_
2_8
0
50
100
150
19911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013
11
1 11 1
11 1
1
1 1
1
1
1
1
1 1
11 1
1 133
3
3
33
3 3
3
3
3
3
3
3
3 Age_
3_8
0
50
100
150
19911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013
1 1 11 1
1 1 11 1 1
1 1
1 1
11
1 11
1
1 13 3
3
3
3
3
3
3
3
33
3
3
3
3
Age_
4_8
0
20
40
60
19911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013
1
1
1
1
11
1 1 1
1
11
1 1
11
1
1 1
11
11
3 3 3
3
3
3 3
3
3
3
3
3
3
3
3
Age_
5_8
0
5
10
15
20
19911992199319941995199619971998199920002001200220032004200520062007200820092010201120122013
1
1
1
1 11
11
11 1
1
1 11 1
1
1
1
1
1
1 1
33
3
3
3
3
33
3
3
3
3
3
3
3
Figure 7.3.2. IBTS index in Skagerrak (area 8) by quarter (1 and 3) and age.
ICES WGNSSK REPORT 2013 423
0 5 10 15 20 25
020
4060
IBTS CPUE East NS
Age_2_8
Age
_2_7
R2= 0.2
5 10 20 30
020
4060
80
IBTS CPUE East NS
Age_3_8
Age
_3_7
R2= 0.1
5 10 15 20 25
020
40
IBTS CPUE East NS
Age_4_8
Age
_4_7
R2= 0.4
5 10 15 20
05
1015
IBTS CPUE East NS
Age_5_8
Age
_5_7
R2= 0.0
20 60 100 140
050
100
IBTS CPUE East NS
Age_2_8
Age
_2_7
R2= 0
0 50 100 150
040
8012
0 IBTS CPUE East NS
Age_3_8
Age
_3_7
R2= 0.0
5 10 20 30
515
2535
IBTS CPUE East NS
Age_4_8
Age
_4_7
R2= 0.3
0 5 10 15 20
05
1015
IBTS CPUE East NS
Age_5_8
Age
_5_7
R2= 0.3
Figure 7.3.3 correlation between IBTS index at age in the Skagerrak (area 8, x-axis) and in the Eastern North Sea (area 7, y-axis). Quarter 1 : 1991-2013. Quarter 3 : 1997-2012.
424 ICES WGNSSK REPORT 2013
Figure 7. 3.4 Trends in the spawning-stock biomass index (cpue of fish above 25 cm, g/hour) in the local Skagerrak components Eastern and Western (IBTS). The dotted line is a loess smoother (span 0.5).
ICES WGNSSK REPORT 2013 425
Figure 7.4.1. top : SSB for the North Sea stock, with and without the Skagerrak landings data included in the assessment. Bottom : differences in North Sea plaice assessment with and without the Skagerrak landings included.