ABSTRACT

Ecopath with Ecosim (EwE) whole-ecosystem models were built for the English Channel (ICES areas VIId and VIIe) for the time periods 1973 and 1995. Using Ecosim, the 1973 model was run forwards with a time-series of fishing mortality data to assess how realistically it predicted the changes in biomass that had occurred. The parameters for both models were modified so that the biomass trends reflected stock assessment data. This tuning required slight changes to some of the basic input parameters, the addition of five juvenile groups, and five functions that forced eight groups to react to annual mean water temperature. The final 1995 Ecosim model consisted of 50 functional groups, with nine different fisheries exploiting 31 of these groups. Market prices, fleet profitability and jobs/catch value ratios were used to run policy optimisation with Ecosim. To set extreme boundaries on the possible gains from the Channel fisheries, we initially searched for optima that maximised economic, social, ecological, or rebuilding for recreational species criteria. Netting and lining were the most profitable fleets and also created the most jobs, so they were significantly increased for the economic and social optima. Using ecological and rebuilding optima, on the other hand, greatly reduced the fishing fleet. Trade-off frontiers were created by weighting each of the objective functions differently and these, along with the results of Rapfish, a rapid appraisal technique that determined the sustainability of the fisheries, were used to generate three robust management alternatives that were assumed to be most beneficial to Channel stakeholders. The effect of climate change was incorporated by running the model for two scenarios where the average sea temperature increased by 0.15 C and 0.3 C per decade. Some of the inherent uncertainty of the data was accounted for by varying vulnerabilities, sea temperatures, the discount rate, and by using a closed loop optimisation analysis. In the light of these whole-ecosystem simulations, we suggest that management of the English Channel for sustainability will require changes to both the fishing fleet and to the European management structure.

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