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The English Channel : subtitle a mixed fishery, but which mix is best? Stanford, Richard James

Abstract

Ecopath with Ecosim ecosystem models were built for the English Channel (ICES areas Vlld and VIIe) in 1973 and 1995. The 1973 model was run forwards in time with a timeseries of fishing mortality data to assess how realistically the model 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, and the addition of 5 juvenile groups and 5 functions that forced 8 groups to react to annual mean water temperature. The final 1995 Ecosim model consisted of 50 groups, with nine different fisheries exploiting 31 of these groups. The market price, fleet profitability and jobs/catch value ratio were entered into Ecosim to run policy optimisations. To set extreme boundaries of possible gains from the Channel, initially the computer searched for the economic, social, ecological and rebuilding for recreational species optima. Netting and lining were the most profitable fleets and also had a high jobs/catch value ratio so were significantly increased for the economic and social optima. The ecological and rebuilding optima reduced the fleet to nearly zero. 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 the special interest groups (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 and the discount rate and by using the 'closed loop' optimisation analysis. A discussion of the future management of the Channel followed, suggesting that changes to both the fishing fleet and the European management structure were required for sustainable management of the English Channel.

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