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Case study 1: Approach

Data and parameters

Stock data

Catch-at-age, indices of abundance and biological data are taken from The North Sea Demersal Working Group (ICES, 2005, 2006).

Fleet data

Data on catch composition by stock and fleet are taken from both ICES and the STEFC database.



Packages used are FLCore Ver 2.2.1, FLSR, FLBRP, FLAssess and FLHCR

Data inputs are modelled by the FLCore classes FLStock, FLIndex, FLIndices, FLBiol, FLFleet and FLFleets, which contain all the input data required for and the outputs from the conditioning.

Conditioning of Operating Model

Historical Estimates of Time Series

The Operating Models for all scenario evaluations were conditioned on WG group estimates of the historical status of the stock and the fishery. Thus, it is assumed that the WG estimates are correct. For the spatially explicit model (chapter 7.3 in Grift et al. 2005), spatial data from the BTS were used in addition. The used method for conditioning was a trial and error process (described in Poos et al. 2006,Pastoors et al. 2006, 2007), in which parameters were modified until the model gave a good fit to the data. The pros and cons of this approach are discussed by Pastoors et al. (2007).

Biological Parameters

Parameters for Von Bertalanffy growth and length-weight relationships in Grift et al. 2005 were derived from regression analysis of survey data available at IMARES.

Stock Recruitment Relationships

Stock recruitment relationships were fitted to the WG estimates. Ricker as well as Beverton-Holt were used as alternative scenarios.

Fisheries & Fleets

Only one fishery is considered, and only Grift et al. 2005 considered more than one fleet (namely two). In that case the parameters were based on expert knowledge within IMARES and derived by the trial and error method mentioned above (parameters were adjusted until the historical model showed a good fit to the data).


Economic modeling has been incorporated in the model of Machiels et al. 2007 (STECF 2006). The economic parameters used have been derived from the data collected by LEI in the framework of the National program (Netherlands Directorate of Fisheries et al 20061)). Fishermen’s behaviour was assumed to be consistent with the described behaviour in the management procedure. Information on plaice and sole landings was retained from the biological model and income from other species was assumed proportional with effort. Special attention has been given to model price elasticity. In particular the coherence of prices of fish from different stocks and species and the definition of markets has been considered. First results are included in an annex to the STECF report 2)). The causality part of the model comprises considerations about the cause and the effect, and the recursive procedure comprises break down of general economic equations into simpler operational, repeatedly nested equations taking into account the causality condition, (see http://en.wikipedia.org/wiki/Recursivity and http://en.wikipedia.org/wiki/Recursivity for good explanations of the concepts). The economic modeling part takes into account full feed back between the fish stocks and the fishing fleets. It is flexible with respect to included species and how the fleet segments are categorized. However, it basically follows the DCR definitions (Commission Regulation (1639/2001) with respect to the fleet, costs and earnings. The application to flatfish implies that relevant species and fleet segments are included but the basic structure of the model remains the same. Next to this approach, economic modeling has been extended within the IMARES model. Economic information has been incorporated in FLecon and production functions have been developed to model the fishing behaviour more adequately. Specific attention is being given to model economic decisions under mixed (input and output restrictions) management constraints in the case of mixed fisheries.

Reference Points

The limit and precautionary reference points were taken from ICES. The target Fs for the evaluation and impact assessment of the EC proposal for a North Sea flatfish management plan (Machiels et al. 2007, STECF 2006) were taken from that proposal.

Observation Error Model

The observation error of the catches as well as the tuning series assumed was a normal distribution around the actual value with a CV of 10% (Poos et al. 2006; Pastoors et al. 2006, 2007).

Management Procedure

The stock assessments and short term predictions are based upon FLXSA and FLSTF. The management measures derived from these and subsequently implemented were specified by the commissioners of the respective scenario evaluations. Compliance was full. However, various fleet behaviour scenarios were considered (e.g. Machiels et al. 2007). For example, the EC proposal for a flatfish management plan specifies TACs as well as days at sea restrictions. However, the two TACs and the days at sea do not necessarily restrict the fishery to the same extent. Several scenarios can be envisaged about whether and how the fleet continues fishing for one species when the TAC for the other species has been exhausted, or whether the fleet continues fishing using up the allowed days at sea even after both TACs have been exhausted (Machiels et al. 2007).


Including plan for future work and results ( Grift et al. 2005, Poos et al. 2006, Pastoors et al. 2007, Machiels et al. 2007, STECF 2006,

     [[http://www.cvo.wur.nl/default.asp?ZNT=S2T2O-1P267|Machiels et al. 2008]], 
     Oostenbrugge et al. 2008)


Where the work was commissioned by external clients, reports have been distributed accordingly: Grift et al. (2005), Poos et al. (2006), and Machiels et al. 2007 to the Dutch ministry of LNV (Agriculture, Nature, and Food Quality), and STECF 2006 to the EC. In addition, the work of |Poos et al. (2006) and Pastoors et al. (2006) was circulated in the North Sea RAC, and was used in the ICES SGMAS in January 2006. This work was subsequently presented at the ICES symposium on Fisheries Management in Galway in June 2006 and has been published as a peer-reviewed article (Pastoors et al. 2007). Machiels et al. 2007 was in addition used in the ICES WGNSSK in September 2006, and served as a basis for the work by STECF 2006. Machiels et al. 2008 was used in the ICES WGNSSK in May 2008.

Links to Other Work

All the work discussed here is carried out in close connection with the EC-funded COMMIT project. In addition, the work by Poos et al. (2006) and Pastoors et al. (2006) is linked to work carried out by the ICES SGMAS. And the work by Machiels et al. 2007 is linked to work carried out by the ICES WGNSSK and STECF 2006.

In connection with the development of the economic AHF model for dynamic fleet capacity change, a multi-fleet and multi-species example was constructed, comprising dutch beam-trawlers catching plaice and sole in the North Sea. This work is reported in Hoff and Frost (2008). The equations used to evaluate the dynamic fleet capacity change in the AHF model are described shortly in Appendix 4 of ECONOWS (2008). A more detailed description of the AHF model in the form it is used in the present context is found in Hoff and Frost (2006).


Anon. (2002). Annual Economic Report 2002. Economic performance of selected European fishing fleets.

Boon, A. R. and D. Delbare (2000). By-catch species in the North Sea flatfish fishery (data on turbot and brill) preliminary assessment (DATEBRAS). Final report, EC 98/078, RIVO. C020/00.

EC (2001). COUNCIL REGULATION (EC) No 1639/2001 of 25 July 2001 establishing the minimum and extended Community programmes for the collection of data in the fisheries sector and laying down detailed rules for the application of Council Regulation (EC) No 1543/2000. No. 1639/2001.

Grift, R., W. Dekker, O. van Keeken, S. Kraak, B. van Marlen, M. Pastoors, J.J. Poos, F. Quirijns, A. Rijnsdorp, I. Tulp. 2005. Evaluation of management measures for a sustainable plaice fishery in the North Sea. RIVO report C019/05.

Hoff, A., Frost, H. 2006. Economic response to harvest and effort control in fishery. FOI report.

Hoff, A., Frost, H. 2008. Modelling combined harvest and effort regulations: the case of the Dutch beam trawl fishery for plaice and sole in the North Sea. ICES Journal of Marine Science, 65(6), pp 822-831.

ICES (2005). Report on the Assessment of Demersal Stocks in the North Sea and Skagerrak. Bergen, Norway, 7-16 September 2004. ICES CM 2005/ACFM:07.

Machiels, M.A.M., Kraak, S.B.M., van Beek, F.A. 2007. Evaluation of a management plan as proposed by the European Commission in 2006 for fisheries exploiting stocks of plaice and sole in the North Sea. IMARES report C011/07

Netherlands Directorate of Fisheries, Netherlands Institute for Fisheries Research, LEI B.V. (Institute of Agricultural Economics) (2006). Technical Report of Activity 2005 – THE NETHERLANDS, detailing the state of completion of the aims set at the time of the drawing-up of the minimum programme and of the extended programme of the Data Collection Regulation. (http://datacollection.jrc.cec.eu.int/NP/2005/Technical%20Report%20NL%202005.doc)

Pastoors, M. A., Poos, J. J., Machiels, M.A.M. 2006. Evaluation of a proposed management plan for Northsea flatfish. http://flr-project.org/doku.php?id=applications:nsrac

Pastoors, M. A., Poos, J. J., Kraak, S. B. M., Machiels, M.A.M. 2007. Validating operating models in simulations of management plans and the implications for how the results can be communicated. ICES Journal of Marine Science. 64:818-823

Poos, J. J., Machiels, M.A.M., Pastoors, M.A. 2006. Investigation of some management scenarios for North Sea sole and plaice in 2006 and beyond. CVO report 06.004.

STECF 2006. Impact assessment of long-term management plans for sole and plaice. http://old-stecf.jrc.it/meetings/sgeca/0605/stecfreportanannex.pdf


EFIMAS Contribution to the work

Participants: Laurence Kell, Ayoe Hoff, Hans Frost, Charlotte Deerenberg, Clara Ulrich Rescan, Graham Pilling, Hans van Oostenbrugge, Jan Jaap Poos, Marcel Machiels, Martin Pastoors, Sarah Kraak, Trevor Hutton, Wim Demaré

1) Netherlands Directorate of Fisheries, Netherlands Institute for Fisheries Research, LEI B.V. (Institute of Agricultural Economics) (2006). Technical Report of Activity 2005 – THE NETHERLANDS, detailing the state of completion of the aims set at the time of the drawing-up of the minimum programme and of the extended programme of the Data Collection Regulation. (http://datacollection.jrc.cec.eu.int/NP/2005/Technical%20Report%20NL%202005.doc
2) STECF 2006). Fleet dynamics were not included in the model so far and thus the economic results are given as ‘gross added value’. This economic component has been used for the analyses of the impact assessment of the EC proposal for a North Sea flatfish management plan together with the EIAA model ((STECF 2006). Neither of these models are, however, completely able to take into account full feed back between fish stocks and fleets when several harvest rules applies. These models have together with the TEMAS model formed basis for development of a general model that is capable of taking into account several harvest rules on the output side (TAC) and the input side (effort) without violating causality and the recursive process (Hoff and Frost, 2006((Hoff, A., Frost, H. 2006. Economic response to harvest and effort control in fishery. FOI report.
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