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This report describes the combined ex post and ex ante evaluation of the multiannual plan for sole and plaice in the North Sea as laid out in Council Regulation (EC) No 676/2007. It extends previous reports by IMARES (C114/09, C104/10). This plan has been in place since 2007. The plan aims to ensure, in its first stage, that stocks of plaice and sole in the North Sea are brought within safe biological limits, i.e. above Bpa and below Fpa. Following this, and after due consideration by the Council on the implementation methods for doing so, the plan will ensure that the stocks are exploited on the basis of maximum sustainable yield and under sustainable economic, environmental and social conditions. This report extends work previously carried out by Wageningen IMARES evaluating the multiannual plan for plaice and sole in the North Sea as described in Council Regulation EC 676/2007 (Machiels et al. 2008). That evaluation has been redesigned to take into account comments and criticisms highlighted by two ICES reviewers. The ex ante evaluation of the plan includes an examination of its implementation, and the stock and fleet dynamics in relation to the measures and objectives of the plan. The stock dynamics were evaluated using two different stock assessment models: an XSA model and a statistical catch at age (SCA) model. Changes in fleet dynamics were evaluated in terms of overall fishing effort and number of vessels in the Dutch beam trawl and otter trawl fleets. The regulations in the Council Regulation have been used as the basis for establishing TACs for North Sea plaice and sole for the last two years. However, the actual implementation of these regulations has required a degree of interpretation by those implementing them. The regulations by themselves lack transparency, without proper specification of how they are to be implemented (e.g. how Fsq is to be calculated) and how the achievement of objectives is to be assessed (neither in terms of the model used to specify this, nor in the level of uncertainty that is acceptable). The multiannual plan, without further specifications than the regulations alone, can appear to lack direction. A simple 10% reduction from an unclearly defined Fsq does not necessarily steer the stock towards the objectives. This is especially true given retrospective problems in the North Sea plaice and sole stock assessment. A stepwise decrease in the ‘distance’ between current F and the target F, while potentially invoking the 15% TAC change more often, may be more successful in assuring progress towards the objectives and prevent issues such as the projected increase in sole F from 2008 to 2009. The rationale for the target fishing mortality reference points in the long term management plan is not given in the Council Regulation. The objective F for the North Sea plaice stock is similar to, though slightly high than, the current proxy of FMSY for this stock as used by ICES. In the case of North Sea sole, the management objective F lies within the broad range of potential proxies for FMSY for the stock. North Sea plaice F is currently below the target F level while, a significant decrease in the F of North Sea sole is still required, especially considering that the current management F for the stock is likely to represent an increase in F from 2008 to 2009. In this context, the long term management plan will steer towards a further decrease in fishing effort by the main fleets targeting sole and plaice. Under the multiannual plan, the North Sea plaice TAC has been increasing. This increasing trend is likely to persist as long as the stock continues to recover because fishing in the near future should fluctuate around what is considered to be the optimum F for long term sustainable yields. Discarding levels remain high, but currently they are near the lowest level of the past ten years and show a downward trend. North Sea sole TACs have stabilised to a degree under the multiannual plan in the most recent years, but these are likely to continue to fluctuate depending on the strength of incoming year classes. The data available to analyse the stock dynamics under the multiannual plan allow the following conclusions to been drawn with respect to the chosen reference points and the safe biological limits of the stock: Spawning Stock Biomass (SSB) of both species have increased since the implementation of the plan. The XSA assessment for plaice (giving only point estimates), indicates that SSB has been larger than Bpa for two consecutive years. The SCA assessment (following Aarts and Poos 2009) indicates that plaice indeed has a larger than 95% probability of having reached a stage where the SSB is above Bpa for two consecutive years. For sole, the XSA stock assessment indicates that SSB has been above Bpa for two consecutive years. An alternative assessment including uncertainty estimates indicate that the probability of being above Bpa in not yet larger than 95%. The annual fishing mortality rates (F) of the two stocks have been declining in recent years. The North Sea plaice stock is now fished at a level below the management regulation target for this stock (0.2 per year). According to the latest assessment results, both stocks appear to be within the precautionary zone with regards to SSB and F in 2008. Hence, despite a lack of clarity in the implementation of the management regulations, the multiannual plan, given the current perception of the stock, appears to be resulting in stock trajectories and fishing levels moving towards the desired objectives and is, therefore, in line with the principles of the precautionary approach. In the first year of its implementation (2008), it appears that the effort regulations defined for the multiannual plan have been having the desired effect. Overall fishing effort has declined, along with a decrease in the size of the main fishing fleets utilising these resources. These reductions in effort seem to be compensating for issues relating to the practical application of management regulations on the setting of TACs. In the ex‐ante evaluation, three different approaches were used to test the effects of the management plan. The first was a yield curve analysis for the two stocks under different stock and recruit relationship assumptions to assess the equilibrium fishing mortality targets in the plan. The second approach is a projection of the two stocks under the rules of the plan, varying only future recruitment under different assumptions. Finally, the third approach is a full feedback MSE approach where in addition to the biology the fisheries system is also modelled. In order to show that the management plan is precautionary for the two species under consideration according to ICES, we use the Criteria agreed during WKOMSE to be applied in the evaluation of Harvest Control Rules/Management Plans in relation to precautionary reference points. The results presented here suggest that the multiannual plan can be considered to be precautionary for both of the managed stocks according to the criteria described by WKOMSE for the evaluation of multiannual plans. The plan allows for increases in yield to 2015 and in the long term while reducing the current levels of F. There is a very high likelihood of stock growth in terms of SSB for both stocks. Both the simple stock projections and full feedback MSE analysis showed that F is likely to remain at low levels allowing for increases in stock biomass. Caution needs to be taken in the interpretation of the MSE, and stock projection results because future projections take the stock to outside the range of historic observations. But by examining the performance of the plan at the lower ends of the simulation ranges and considering ‘worst case’ recruitment scenarios the likely risk of a management failure can be considered to be adequately estimated. The results presented show that the plan is very likely to be precautionary but it is more difficult to assess whether it achieves the goals of long term yields and sustained healthy populations. This is essentially a question over whether the F targets specified for the two stocks are reasonable and whether in practice they can be achieved simultaneously. The former relies of the definition of MSY for these two stocks and the corresponding stock sizes that can deliver these yields while the latter depends on how fisheries behaviour and gear selection changes into the future. Given the uncertainty associated in the estimation of Fmsy reference points and that expert opinion has been incorporated into the determination of target F points, the targets as they stand seem plausible. Regardless, it is clear that both stock growth and long term increases in current yield levels are likely should the multiannual plan be implemented.

For most pelagic fish stocks that are exploited in EU waters, long-term management plans are established and used for TAC setting. North Sea horse mackerel was classi-fied by ICES as a data-limited stock (DLS) in category 5 with only landings data avail-able in 2012. This led to the advice for 2013 being a TAC which represented a reduction of 20% of recent landings as a precautionary measure. In response, the main stake-holder in the fishery - the Dutch Pelagic Freezer-trawler Association (PFA) - sought collaboration with IMARES to develop a multi-annual plan for this stock. The plan should specify a rationale for establishing TACs through a Harvest Control Rules (HCR) and it should stipulate how the stock could be ‘moved up the ladder’ of the DLS categories; ultimately aiming to progress it to become a data rich (category 1) stock in the medium term. As a DLS, no stock assessment has previously been adopted as a basis for advice for North Sea horse mackerel. In recent years, some explorative work on data availability for the stock has been done by the ICES Working Group on Widely Distributed Stocks (WGWIDE), and this work has been taken further in this report to produce two potential indices of stock size from the IBTS Q3 survey data. A thorough analysis of the IBTS data for North Sea horse mackerel is also presented. A modelling framework was developed (the JAXass model) to obtain plausible estimates of stock size using the indices created from the IBTS data. There are numerous difficulties fitting an assessment model for this stock: unclear stock boundaries, difficulty aging horse mackerel, lack of strong cohort signals in the catch-at-age data, no targeted survey of abundance for North Sea horse mackerel, and the available survey data not covering one of the main fishing grounds for the stock (ICES Subarea VIId). In addition there are some conflicting signals between the catch and index data, espe-cially since the mid-2000s. Hence no single ‘best’ assessment model has been provided. Rather a suite of plausible models are used together to test the robustness of the stock to potential future management options. Fishing mortality reference point values were calculated by running long-term projections at varying levels of F. FMSY (the fishing mortality providing the maximum yield at equilibrium) is estimated to be in the range 0.08-0.24, depending on the choice of stock recruit relationship. A more precautionary and better estimated robust proxy for FMSY is proposed: F35 (the fishing mortality that leads to SSB at 35% of virgin biomass at equilibrium). Values for F35 range from 0.1-0.14 depending on the choice of stock–recruit relationship. The available data suggest that the North Sea horse mackerel stock is currently at a low biomass in relation to levels in the late 1990s. Recent IBTS surveys have had a large proportion of 0 hauls and low cpues. Alternative methods of calculating the index from the raw data (e.g. delta-lognormal method, GLM analysis or simple mean cpue of all hauls) indicate that the stock is near the lowest level observed. As a result, all explora-tory assessment models fit to these data estimate that current SSB is near the lowest observed. Fishing mortality has been above fishing mortality levels suggested for Fmsy (proxies), especially in the recent past and a reduction in catches in the short term is therefore required to allow for recovery of the stock. The special request sent to ICES asked “to assess whether the proposal as presented in Annex A is precautionary and if it will deliver Fmsy by 2015 or 2020 at the latest”. It was decided at the WKHOMMP meeting that with simulations including a constant catch or a constant F, the focus of the evaluations should rather be on what level the catch could be in the short term in order to reverse the declining trend in the stock than on the performance of the HCRs. To this end, the following procedure was followed: 1. Scenarios of constant catch and constant F were examined to see what level of catch or F would allow for recovery of the stock in the short term. 2. On the basis of these runs, viable short term management options are presented. 3. An initial examination of the potential HCR options is also presented, but to allow for a meaningful compari-son of these some stock recovery is required first. HCR performance statistics were tailored to short-term considerations to give an idea of the short-term prospects for the fishery and the short-term recovery of the stock (by 2020). A recovery of the stock above SSB2012 (lowest observed, candidate for Blim) is considered the first priority. This recovery is unlikely by 2015, but should be expected at least by 2020. A re-evaluation of potential HCRs looking at longer term management considerations should be undertaken in 3-5 years, unless anything changes in our un-derstanding of the stock in the meantime that would require a re-evaluation of man-agement options. In terms of providing an estimation of what level of catch the stock could take in the short term, the MSE results are highly sensitive to the choice of stock–recruit relationship (SRR). However, regardless of the choice of SRR, the results from the exploratory assessment model runs and the evaluation of expected future performance of the stock are rather pessimistic. Depending on the SSR scenario (segRick or decLim), the suggested level of catch in the next few years which could allow for a reversal in the de-clining trend in SSB and bring SSB to above the SSB2012 level ranges from 2.5kt to 10kt. Recent catches of this stock have been in the range of 20-25kt, so this represents a significant reduction in fishing opportunities. Determining what levels of TACs will lead to this level of catch is problematic, because of the consistent underutilization in the TAC observed in recent years due to the ab-sence of the Danish fishery. In order to reduce the fishing opportunities for those fleets who do utilize their quota not more drastically than necessary, this underutilization could be taken into account when establishing the level of the TAC. In addition, a reduction in TAC would naturally only be effective if the TAC would be restrictive to the collective of all countries exploiting the stock, i.e. including Norway, which has caught highly variable but occasionally substantial quantities. Investigation of how the HCRs performed compared with each other in the long term, was investigated as a hypothetical exercise however. The current evaluation results, suggest that the HCR based on a log-linear regression interpretation of the slope with a lambda value of 0.5 performs relatively well. It showed a lower interannual variabil-ity than when a 5 year slope was used but still responded most quickly to changes in the trend of the index. This is most likely because, at the time when the declining trend in the SSB starts to reverse and in fact is level for a few years, the 3-year slope HCR keeps the TAC also stable, while the 5-year HCR continues longer with declines, after which quickly changes to increases again. At the same time it indicated more recovery in SSB than the DLS rule or the HCR including a 20% constraint in TAC change. There is some anecdotal evidence suggesting that one or more relatively strong year-classes may have been produced in recent years in the North Sea: pelagic fishers have reported substantial quantities of juvenile horse mackerel in the Southern North Sea during their fishery, a near shore survey conducted in the ‘Voordelta’ area by IMARES caught a large number of juvenile horse mackerels in the summer of 2013, and the by-catch quota provided to the Dutch demersal fleet was exhausted approximately midyear in 2013, which was considered very early compared with other years. If these are a true reflection of actual events, then this may lead to a more rapid recovery of the stock than the results of the current study suggest. This should then be measurable in the IBTS survey data in upcoming years, in which case management measures can be revised accordingly. Generally speaking, any long-term management plan is most effective when its measures apply to all fisheries exploiting the stock and when catches can be identified as originating from that stock with some certainty. Considering the potential of mixing between Western and North Sea horse mackerel occurring in area VIId, better insight in the origin of landings from that area will be a major benefit, if not crucial, for im-provement of the quality of future scientific advice and thus management of the North Sea horse mackerel stock. One way of possibly distinguishing between individuals of the two stocks is with the GCxGC-MS (Gas chromatography x Gas chromatography–mass spectrometry). A pilot project aimed at determining whether this technique could be used for distinguishing between Western and North Sea horse mackerel is currently underway.

A rebuilding plan for the 2+3KLMNO Greenland halibut stock developed by NAFO Fisheries Commission has been in effect since 2004. Under the plan, ad hoc TAC reduction steps were specified to 2007. The most recent assessment of this stock indicates that the rebuilding plan has been ineffective in initiating any recovery. Fishing mortality is still at high levels and spawner biomass has remained at very low levels. Management Strategy Evaluation provides a way of examining the performance of candidate management strategies with respect to rebuilding the stock. In particular, it allows the robustness of these strategies to be considered relative to alternative operating models of the “real world”, for example the nature of the stock-recruit function for this stock. A preliminary MSE presented at the 2007 NAFO Scientific Council meeting has been updated following the NAFO SC Study Group on Rebuilding Strategies for Greenland Halibut meeting held in Vigo in February 2008. The analysis is carried out in FLR (Fisheries Libraries in R) environment, an open source framework for the development and evaluation of management strategies. A reference set of 20 possible operating models is presented, four of which are examined further. Results are presented in detail for five potential management strategies tested on these four operating models. A suite of performance statistics for this stock are used to assess these management strategies. The results of this MSE exercise are evaluated in the context of the NAFO approach to fisheries management and the potential for further progress with regard to the application of MSE on this stock in general is considered., http://www.mth.uct.ac.za/maram/pub/2008/GH_NAFO_SCR_Doc_08-25.pdf

Plaice in Kattegat and Skagerrak have traditionally been considered as one stock unit. However the collected information on biology and fishery in areas between the North and Baltic Seas suggest changes are needed in assessment units as well as in management areas. Plaice in Skagerrak (Division 20) is now considered to be closely associated with plaice in the North Sea and is proposed to be included in the North Sea plaice stock assessment, although it is recognized that local populations are present in the area. Therefore, specific management of the Skagerrak plaice is suggested. Plaice in Kattegat (Division 21), the Belts (Division 22), and the Sound (Division 23) is considered a stock unit and is proposed to be assessed as such. However, separate management by area is also suggested to assure the preservation of the local populations. Plaice in the Baltic (Divisions 24–32) is considered a stock unit and is proposed to be assessed and managed as such. Pragmatic options are suggested for empirical harvest control rules accounting for the dynamic of local abundance, using a survey‐based biomass indicator. For the future, new scientific analyses should be developed to better inform the origin of the catches, provided that additional resources are allocated to the annual monitoring of different stocks and components. Such information would provide on‐going quantitative information on the degree of mixing of the various components, potentially allowing a more accurate assessment, management, and conservation of the status of these