7 Plaice in Skagerrak (IIIaN)

Transcription

1 ICES WGNSSK REPORT Plaice in Skagerrak (IIIaN) Significant changes have been provided to the assessment of this stock in 0. Before then, ICES presented analyses for the combined area IIIa (Skagerrak + Kattegat), but there hadn t been produced a final assessment since 005 because of notable discrepancies in the catch at age and tuning information. A dedicated workshop was convened in early March 0 (ICES WKPESTO 0) to address these issues more specifically, following the recommendations from ICES WKFLAT 00. 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 management areas. WKPESTO considered plaice in Skagerrak (Division 0) to be closely associated 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 possibilities for combined or disaggregated assessments of current defined stocks. In particular, WKPESTO considered plaice in Kattegat (Division ), the Belts (Div. ) and the Sound (Div ) as one stock unit and proposed it to be assessed as such. Last year, WGNSSK 0 produced both the old setup (combined assessment Skagerrak-Kattegat) and the new setups (Kattegat, and assessment and North Sea- Skagerrak assessment, section 8). In addition, an answer to an EU-Norway request dealing with management options for Skagerrak plaice was also produced (ICES 0). The new setup was accepted as the basis of the 0 advice, and the TAC for 0 was consequently de-coupled between Kattegat and Skagerrak. In 0, ICES does not present the combined IIIa assessment, but only the considerations specific to Plaice in Skagerrak. The Plaice Kattegat-SD- 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 Ecosystem aspects A general description of the ecosystem is given in the Stock Annex. 7.. Fisheries A general description of the fishery is given in the Stock Annex. Technical Conservation Measures Minimum Landing Size is 7 cm.

2 404 ICES WGNSSK REPORT 0 Changes in fleet dynamics A detailed description of the fishing activities in area IIIa is available in STECF (0), although results are presented aggregated for the annex IIa-Area b of the North Sea cod area, i.e. including North Sea (IV), Skagerrak (IIIaN) and Eastern Channel (VIId) In 0, 0% of the plaice landings in Skagerrak came from Fully Documented Fisheries, 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 0, 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 plan. The 0 ICES advice sheet for Skagerrak plaice has included considerations for this. 7.. ICES Advice Until 0, ICES produced advice for the combined area IIIa. Given that no assessment was produced, ICES advice was only based on trends in recent catches. In 0, 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 control 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. (0) as modified by ICES WKPESTO (0) and ICES WGNSSK (0). On these considerations, ICES advised that catches in Skagerrak could increase by 7% compared to the recent average catch of the last years, corresponding 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.. 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 Skagerrak, on the basis of the putative linkages between this stock and North Sea Plaice. In 0, The TAC had been decreased by 5% compared to 00, to 9 98 t (7 950 t in Skagerrak and 988 t for Kattegat), following the EC Policy Paper (COM(00) 4), This corresponded to the level of landings in 00. (Table 7..4). +Evaluation+of+Fishing+Effort+Regimes+pII_JRC7678.pdf and 6th-april-0-copenhagen/

3 ICES WGNSSK REPORT In 0, the TAC was rolled over to the same level as 0. In 0, the TAC for Skagerrak was decoupled from the TAC in Kattegat for the first time. The TAC was increased by 5% compared to 0, on the basis of the increasing stock and TAC in the neighbouring North Sea. Since 00 the TAC uptake has been close to 00%, (Figure 7..) Effort restrictions in the EC were introduced in 00 (annual annexes to the TAC regulations) for the protection of the cod stock in North Sea, Skagerrak and Eastern Channel. In 009, the management programme switched from a days-at-sea to a kwday system (009 Council Regulation (EC) N 4/009), in which different amounts of kw-days are allocated within each area by member state to different groups of vessels, depending on gear and mesh size. Effort ceilings are updated annually. Plaice in Skagerrak is primarily caught by Danish seines with >0 mm mesh size with limited by-catch of cod; however, this fishery is included in the regulated TR category and has been deemed to annual effort ceilings reductions. 7. Data available 7.. Catch The official landings reported to ICES were not distinguished between Skagerrak and Kattegat until 0. Official statistics for Skagerrak are only available for 0. The annual landings used by the Working Group, available since 97, are given by country in Tables 7... Denmark usually stands for more than 90% of the landings (96% in 0). Previously, misreporting had been considered to potentially occur in the area between the North Sea and the Skagerrak, and notably in the ICES rectangle 4F8 which is shared between both areas and represents a large part of the landings (Figure 7..). However, extensive checks using VMS data (for vessels >5m) and investigation of departure harbour for the vessels <5m showed that no obvious pattern of misreporting could be detected, and that only minor mismatch occurred between VMS and logbooks information (ICES WGNSSK 0, ICES WKPESTO 0). In 0, 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 ) 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..). There are almost no landings from age plaice, and generally poor tracking of the cohorts (Figure 7..). A discards time series for the full area IIIa from Denmark and Sweden over 00-0 is available, but these data have not been re-compiled yet to distinguish between Skagerrak and Kattegat (the work is planned for the 05 benchmark). However, 0 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 (%). Missing discards data for the other metiers were raised using all available discards information except those from the Swedish Nephrops and Pandalus fisheries using

4 406 ICES WGNSSK REPORT 0 sorting devices, which have very low landings and consequently relatively high discards rates. Average discards age composition was applied to all unsampled strata. 0 discards were estimated at 05 tonnes, corresponding to a discards ratio to landings of.4 % (=% ratio of discards to catches). 70% of this discards estimates come from sampled strata, and 0% from the raising to unsampled strata. 7.. Weight at age Weight at age in landings is presented in Table 7.. and Figure 7... A major issue for this stock assessment is the extreme variability of the growth patterns obtained from biological samples, with extreme overlap of length distributions of the main ages (ICES, 0 and Ulrich et al., 0). This is considered as the main cause of the lack of year class signal in the catch-at-age matrix. 7.. Maturity and natural mortality Not estimated 7..4 Catch, effort and research vessel data In 0, landings and effort data by gear were computed at the level of the ICES rectangle. 0 Data for the European fleet was available from the STECF online data [ on the basis of the main cod plan categories. 0 data from Sweden, Denmark and Germany were added in the same format. (Figure 7..). Additionally, ICES (0) and Ulrich et al. (0) considered that the area IIIa should b split in various spatial components with potentially different stock origins (Figure 7..4). Since 00, 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..5). Skagerrak landings amount to around 0% of North Sea landings. IBTS data are available in the area IIIaN. Since 007 the WG discussed the limited spatial coverage of the surveys with regards to main fishing grounds. The IBTS sampling 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. Data analyses 7.. Comments from the technical review group 0 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 approved plaice stock represents a divergence from the traditional stock structure where IIIaW is not considered part of the traditional Division IIIa complex. Not having been involved in the discussions, the review group has taken the approach to review the documentation provided for each of the Plaice stock definitions and await the decision on which stock structure is accepted.

5 ICES WGNSSK REPORT 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. (0) 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 assessment 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.. Catch-at-age matrix The Landings-at-age matrix is shown on the figure 7... 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.. Tuning series Catches trends in fishing patterns by the main gear groups across areas were computed (Figure 7..). 0 lpue for the main fishery (TR in Western Skagerrak, 8% of total landings for the stock in 0) have remained at the recent high level. Highest CPUE used to be observed at the western entrance but in 0, these were mainly observed in the Central area. Trends in IBTS area different between spring and autumn (Figure 7..). The autumn survey seems to show consistent high signals for some year classes, and in particular at age the picks correspond to the large year classes 007, 004 and 00 observed in the North Sea. The spring survey is less consistent. However, there are usually only weak correlations between the IBTS abundance indices in Eastern North Sea (area 7) and the Skagerrak (area 8) (Figure 7..) A spatially-disaggregated abundance index from IBTS Quarter (modified from Cardinale et al., 0) has been suggested by ICES WKPESTO (0) and ICES WGNSSK (0). 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 0, the computation of this index was redrawn and made directly calculated from ICES DATRAS database (Figure 7..4 and Table 7..). 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.

6 408 ICES WGNSSK REPORT Exploratory analysis No analytical assessment is presented for this stock. However, a combined assessment, where Skagerrak landings are included in the North Sea catches, is performed (Figure 7.4.). Overall, an addition of around 0% of the catches scales the assessment, with a 5-7% increase of the SSB estimates and a 5-0% decrease in F. The reason 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 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 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. Recruitment 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 7.0 Quality of the assessment The sustained research activity on that stock has finally led to some major changes for this stock (Ulrich et al., 0). 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 approach. As the stock structure is still poorly defined in Skagerrak, the assessment now builds on survey trends (Data Limited Stock category ) 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 structure and growth patterns using a combination of genetics, otolith analysis and hydrodynamic modelling, which may shed new light on the dynamics of plaice population in Skagerrak. A benchmark is scheduled for Status of the Stock It is not possible to provide a reliable status of the stock based on analytical assessment. Since 00 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 exploited unsustainably. Landings have been stable over a long time period, and the

7 ICES WGNSSK REPORT effort of commercial fleets has decreased. There had never been sign of impaired recruitment. The landings and lpue have been high in the recent years. The spring survey indicates 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 survey 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 extent by the increased abundance of the North Sea stock. 7. 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 ), 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 influences the advised catch. The spatially-disaggregated abundance index presented Figure 7..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 decreased recently and that lpue of the main fisheries in 0 have remained around the same high level as in 0, 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 % of the 0 catches), but the actual exploitation 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 years, corresponding to catches of no more than 98 t in 04 (average of landings 00-0 with 0 discards rate of % of catches =9454 t, x.04=98 tonnes). In the depleted Eastern Skagerrak, no directed fisheries should occur and bycatch and discards should be minimized. Alternative options for potential interim management plans In 0, 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 0 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, 0 and Table 7..). The SSB estimated from the combined assessment raised by 0% between 0 and 0 and is well above MSY Btrigger. 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 (+5%) would imply catches in 04 to be no more than 880 t (TAC 0 = 94 t

8 40 ICES WGNSSK REPORT 0 landings x.5 = 0 5 t landings, with % discard ratio to catches = 880 tonnes catches). An increase indexed to the changes in the combined assessment SSB would imply catches in 04 to be no more than 64 t (TAC 0 = 94 t landings x. = t landings, with % discard rate = 64 tonnes catches) This interim harvest control rule should be reconsidered after the assessment benchmark scheduled for early References Cardinale, M., Bartolino, V., Llope, M., Maiorano, L., Sköld M., Hagberg., J., 0. Historical spatial baselines in conservation and management of marine resources. Fish Fish, ICES. 0. Report of the Workshop on the Evaluation of Plaice Stocks (WKPESTO), 8 February - March 0, ICES Headquarters, Copenhagen. ICES CM 0/ACOM:. pp Ulrich et al., 0

9 ICES WGNSSK REPORT 0 4 Table 7... Plaice in Skagerrak. Landings in tonnes. Working Group estimates 97-0, and official statistics since 0. TAC in thousands tonnes Year Denmark Sweden Germany Belgium Norway Netherlands Total TAC ICES estimates Official statistics ICES estimates Official statistics ICES estimates Official statistics ICES estimates Official statistics ICES estimates Official statistics ICES estimates Official statistics ICES estimates

10 4 ICES WGNSSK REPORT 0 Table 7... Plaice in Skagerrak. Landings number at age

11 ICES WGNSSK REPORT 0 4 Table 7... Plaice in Skagerrak. Landings weight at age. CW

12 44 ICES WGNSSK REPORT 0 Table 7.. Plaice in Subdivision 0 (Skagerrak). Biomass indices per local component. NumObs = number of observations, avg.cpue= adult biomass indices (g/hour), sd. = standard deviation. Lowess : lowess smoothed cpue value (span=0.5) West Skagerrak East Skagerrak numobs avg.cpue sd.cpue lowess numobs avg.cpue sd.cpue lowess NA NA

13 ICES WGNSSK REPORT 0 45 Table 7... candidate harvest control rule for an interim management plan (as evaluated by IC- ES, 0) a) If the survey abundance is at or below the lower abundance threshold*, then advise a decrease 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 RISING MSY B trigger Skagerrak TAC increases Skagerrak TAC remains with same rate as NS SSB** (aat same level as previous year (b) STABLE / FALLING Skagerrak TAC remains Skagerrak TAC decreases at same level as previous year (cwith same rate as NS SSB ** (d) Below RISING MSY B trigger Skagerrak TAC remains Skagerrak TAC remains at same level as previous year (eat same level as previous year (f) STABLE / FALLING Skagerrak TAC decreases Skagerrak TAC decreases with same rate as NS SSB ** (gwith 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 rather than the SSB value.

14 46 ICES WGNSSK REPORT 0 '000 tonnes 6 Landings TAC Skagerrak ICES landings ICES catches 8 '000 tonnes Figure 7... Plaice Skagerrak. Upper : total landings Lower : Landings vs. TAC in Skagerrak, Total catches 0 added.

15 ICES WGNSSK REPORT F5 F7 F9 G F5 7 F7 9 F9 G F5 7 F7 9 F9 G F5 7 F7 9 F9 G F5 F7 F9 G F5 F7 F9 G F5 7 F7 9 F9 G F5 7 F7 9 F9 G F5 7 F7 9 F9 G F5 7 F7 9 F9 G Figure 7... EU Landings all gears 00-0 (from left to right then top to bottom) all gears (STECF data). Bubble max size= 4400 tonnes.

16 48 ICES WGNSSK REPORT ple-iiian LandWt landings sampled landings unsam Denmark Germany Netherlands Norway Sweden SDN_DEF_>=0_0_0_all OTB_CRU_90-9_0_0_all SDN_DEF_>=0_0_0_all_FDF OTB_DEF_>=0_0_0_all GNS_DEF_0-9_0_0_all TBB_DEF_>=0_0_0_all MIS_MIS_0_0_0_HC OTB_DEF_>=0_0_0_all_FDF OTB_CRU_90-9_0_0_all_FDF SSC_DEF_>=0_0_0_all_FDF SSC_DEF_>=0_0_0_all GNS_DEF_0-9_0_0_all_FDF GNS_DEF_00-9_0_0_all GNS_DEF_>=0_0_0_all GNS_DEF_>=0_0_0_all_FDF OTB_CRU_-69_0_0_all MIS_MIS_0_0_0_IBC OTB_CRU_90-9_0_0_all MIS_MIS_0_0_0_HC MIS_MIS_0_0_0_HC GTR_DEF_all_0_0_all OTB_DEF_>=0_0_0_all OTB_CRU_-69_0_0_all OTB_DEF_>=0_0_0_all_FDF OTB_CRU_90-9_0_0_all GNS_DEF_all_0_0_all GNS_DEF_all_0_0_all OTB_CRU_ _all MIS_MIS_0_0_0_HC LLS_FIF_0_0_0_all OTB_CRU_-69 all ple-iiian DisWt landings sampled landings unsam Denmark Germany Netherlands Norway Sweden SDN_DEF_>=0_0_0_all OTB_CRU_90-9_0_0_all SDN_DEF_>=0_0_0_all_FDF OTB_DEF_>=0_0_0_all GNS_DEF_0-9_0_0_all TBB_DEF_>=0_0_0_all MIS_MIS_0_0_0_HC OTB_DEF_>=0_0_0_all_FDF OTB_CRU_90-9_0_0_all_FDF SSC_DEF_>=0_0_0_all_FDF SSC_DEF_>=0_0_0_all GNS_DEF_0-9_0_0_all_FDF GNS_DEF_00-9_0_0_all GNS_DEF_>=0_0_0_all GNS_DEF_>=0_0_0_all_FDF OTB_CRU_-69_0_0_all MIS_MIS_0_0_0_IBC OTB_CRU_90-9_0_0_all MIS_MIS_0_0_0_HC MIS_MIS_0_0_0_HC GTR_DEF_all_0_0_all OTB_DEF_>=0_0_0_all OTB_CRU_-69_0_0_all OTB_DEF_>=0_0_0_all_FDF OTB_CRU_90-9_0_0_all GNS_DEF_all_0_0_all GNS_DEF_all_0_0_all OTB_CRU_ _all MIS_MIS_0_0_0_HC LLS_FIF_0_0_0_all OTB_CRU_-69 all Figure 7... Landings and discards information as provided to InterCatch before raising.

17 ICES WGNSSK REPORT 0 49 Landings at age age year landings weight kg year Figure 7... Landings number and landings weight at age (age to 8) in Skagerrak

18 40 ICES WGNSSK REPORT 0 Longitude Skagerrak West Skagerrak East 57 Kattegat West Kattegat East Latitude Figure 7..4 Areas defined within ICES division IIIa. From ICES WKPESTO 0. landings North Sea Skagerrak W Skagerrak E Figure 7..5 Landings in Skagerrak areas and compared with the North Sea.

19 ICES WGNSSK REPORT lpue _SkaW G G G G G G G G G G G _SkaE G G G G G G G G G _SkaW _SkaE Effort G G G G G G G G G G G G G G G G G G G G Landings _SkaW G G G G G G G G G G _SkaE G G G G G G G G G G Figure 7.. Trends in Landings, effort and lpue by gear and Skagerrak area. G=Gillnets fishery, = TR (otter trawls and seines with >00 mesh size), = TR (otter trawls and seines with mesh size).

20 4 ICES WGNSSK REPORT Age 8 Age Age_4_8 40 Age_5_ Figure 7... IBTS index in Skagerrak (area 8) by quarter ( and ) and age.

21 ICES WGNSSK REPORT 0 4 IBTS CPUE East NS IBTS CPUE East NS Age R= 0. Age R= Age 8 Age 8 IBTS CPUE East NS IBTS CPUE East NS Age_4_ R= 0.4 Age_5_ R= Age_4_8 Age_5_8 Age IBTS CPUE East NS R= 0 Age IBTS CPUE East NS R= Age 8 Age 8 IBTS CPUE East NS IBTS CPUE East NS Age_4_ R= 0. Age_5_ R= Age_4_8 Age_5_8 Figure 7.. correlation between IBTS index at age in the Skagerrak (area 8, x-axis) and in the Eastern North Sea (area 7, y-axis). Quarter : Quarter :

22 44 ICES WGNSSK REPORT 0 Figure 7..4 Trends in the spawning-stock biomass index (cpue of fish above 5 cm, g/hour) in the local Skagerrak components Eastern and Western (IBTS). The dotted line is a loess smoother (span 0.5).

23 ICES WGNSSK REPORT 0 45 Figure 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.