T-ONS a swift transportable and user friendly integrative model of the North Sea for decision support

The trade-offs North Sea (T-ONS) model is presented. This is centred upon a simple multispecies Schaefer model where the long term steady state yield of each species is approximated by quadratic functions of fishing mortality rate of all species. To this are added the main mixed fishery constraints and the available economic, social and ecosystem consequences of concern to Ecosystem Based Fisheries Management (EBFM). For ease of transportability this model is written in EXCEL. It can swiftly emulate the long term behaviour of more complex age based North Sea multi-species models and is broadly similar to, but has a wider range of outputs than similar models presented in earlier years and differs from them in how it treats mixed fisheries. The ecsPnce of how it fits the ICES age based SMS multi-species fisheries model and uses the STECF fishing effort data series to mimic multi-fleet constraints is explained. In addition to the fishery outputs, the model provides economic and social outputs both overall and on a fleet by fleet or country by country basis. It also provides an as yet restricted set of good environmental status (GES) indicators. It is designed to be user friendly and so to empower managers and stakeholders to personally explore how different management approaches would affect the trade-offs that are of most concern to them. It also allows managers to see how acceptable their solutions would be to the different interest groups of stakeholders. The T-ONS model is also the basic tool of the Mareframe decision support framework for the North Sea. It may be used either as a decision support tool by itself or used to provide inputs to formal decision support tools such as multi-criteria analysis (MCA).