Evaluation of Management Strategies for the Mixed North Sea Roundfish Fisheries with the FLR Framework Hamon, K. 1 , C. Ulrich 1 , A. Hoff 2 , L. T. Kell 3 . 1 DTU-DIFRES, Technical University of Denmark, Danish Institute for Fisheries Research, Charlottenlund Castle, 2920 Charlottenlund, Denmark 2 FOI, Rolighedsvej 25, 1958 Frederiksberg C, Denmark 3 CEFAS, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk NR33 0HT, England, United Kingdom Email: clu@difres.dk Keywords: Management strategy evaluation, FLR, mixed fisheries, North Sea roundfish EXTENDED ABSTRACT Most demersal stocks keep being overexploited despite the numerous management measures im- plemented. New approaches in methods for pro- viding scientific advice to fisheries management include simulation-based MSE (Management Strategy Evaluation), aiming at identifying man- agement strategies robust to various sources of uncertainties. MSE are simulation models includ- ing management scenarios and allowing for test- ing alternative plausible hypotheses about stocks and fleets dynamics. FLR (Fisheries Library in R) is an open-source collection of tools providing a generic modelling framework for constructing such MSE. FLR has been developed under the statistical computing language “R” in EU-funded research projects, and provides various compatible packages which can be freely combined by the user, thus insuring complete flexibility. In this paper, we present a MSE application to the case study of the North Sea roundfish fisheries de- veloped with FLR. The focus is on mixed-fisheries issues and technical interactions between fleets, including assumptions on fleet behaviour. We show that single-stock management objectives for cod and haddock cannot be achieved simultane- ously using stock-based annual TACs (Total Al- lowable Catch) because of conflicting incentives to the fleets. We show that opposite hypotheses of fishermen behaviour (stop fishing when cod quota is exhausted or fish until haddock quota is ex- hausted while discarding overquota catches of cod) lead to dramatic changes in the probability of reach- ing cod recovery in the short-term.. This empha- sises the need for establishing robust and consistent management plans accounting for main sources of uncertainties and interactions. 1. INTRODUCTION The current diagnoses on commercial fish stocks are rather pessimistic. Most demersal stocks keep being overexploited despite the numerous man- agement measures implemented. Main reasons for failures include scientific uncertainty, gap between scientific advice and management decisions and imperfect implementation of management policies. Learning from that, European scientists are turning toward management strategies robust to these sources of uncertainties, along the MSE (Manage- ment Strategies Evaluation) lines initiated by the International Whaling Commission (IWC, 1993; De La Mare, 1998). MSE should build upon frameworks that allows test of plausible hypothe- ses about the dynamics of the stocks and fleets before implementation (Anon. 2007). FLR (Fisheries Library for R, http://www.flr- project.org) is an open-source collection of tools for the development of bio-economic simulation models of fisheries and ecological systems (Kell et al. 2007). FLR has been developed as a number of packages under R which is a “language and envi- ronment for statistical computing and graphics” available as a Free Software under the GNU Gen- eral Public License (R Development Core Team, 2006) (www.gnu.org/licenses/licenses.html#GPL). By using R, FLR improves the transparency of scientific work; de facto all source codes are avail- able which make them easy to review. In addition, the use of predefined classes allows fixing some data formats which are flexible and generic enough to suit most kind of fisheries-related data and models. The development of FLR is taking place across a large number of research projects funded by EU (European Union) with different purposes and case 2813