| Summary: | 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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