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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/

http://stecf.jrc.ec.europa.eu/documents/43805/394916/12-11_STECF+12-16+-+Evaluation+of+Fishing+Effort+Regimes+pII_JRC76738.pdf

http://stecf.jrc.ec.europa.eu/documents/43805/394916/12-11_STECF+12-16+-+Evaluation+of+Fishing+Effort+Regimes+pII_JRC76738.pdf


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


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.


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.


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


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


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


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


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


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


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


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.


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.


+ +

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.


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.


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


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.


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).


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.


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.


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).


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.

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