mainly by sea birds and benthic scavenger species. In this study, the
information is based on the results of the project “Discards of the
Spanish fleets in ICF5 Divisions” financed by the European Union. This
discard sampling programme covered in 1994 the activities of some of
the most important Spanish fleets, trawlers, gillnets, long liners, and
purse seiners, in ICFS Division VIIIc (Pétez etal, 1996).
Recent expansions of the Ecopath approach (Ecosim and Ecospace)
make it possible to simulate changes in fishing pattern and intensity
through time in an ecosystem framework. Ecosim is a time-dynamic
simulation tool for studying fishery policy options (Walters et al, 1997).
Ecosim includes biomass and size structure dynamics: mixed differential and difference equations and use of mass-balance assumptions for parameter estimation. Time patterns of biomass are predicted by these differential equations, and equilibrium system response under different
exploitation regimes. Ecospace is a mesoscale spatial simulation tool for
predicting spatial patterns and runs the Ecopath model through Ecosim
to check the behaviour of ecosystems. Numerical approximation bv
linearisation, and matrix exponential solution method generate projections towards spatial equilibrium. Walters et al. (1998) describe all the
functions used in Ecospace simulations. To explore the simulation capacity of Ecospace, we defined a base-map of the central area of the
Cantabrian Sea with five habitats: oceanic, shelf break, extemal shelf, internal shelf and coastal waters. We also defined the habitat preferences
of different gears and the movement rates and vulnerabilitv in bad habitats of the 25 trophic groups. To test the impact of management
measures, we located the existing restricted area where the use of trawl
gear is forbidden. Subsequendy, we compared the Ecospace and Ecosim
predictions with the results obtained from bottom trawl surveys carried
out before and after the area became restricted in 1992.
Results
The total biomass supported by the ecosystem is estimated at 226 tons
per square kilometre. Big hake and monkfish present the highest trophic
levels (4.6). As refers to the fish species, the EE indicates that 65 to 95% of
the production are used in the system. It also detected some discrepancies
in the natural mortalitv provided by the model with the values used in
the single species analytical assessmcnt methttds (IQIS reports). The M
values for some groups are slightly higher in the Elcopath model than in
thc WA, where they are assumed to have values between 0.2 and 0.8. As an
example, M for blue whiting (the main food intake for hake, monkfish
and big demersal fish in the area) is higher in the model.
In order to compare the relative role of the pelagic, demersal and benthic
subsystems, the figure presents the major biomass flows diagram of the
Cantabrian Sea ecosystem in 1994, estimated bv Ecopath. Most of the
biomass and production are contained within the pelagic domain. The
main flow is determined by the interaction between phytoplankton,
190
information is based on the results of the project “Discards of the
Spanish fleets in ICF5 Divisions” financed by the European Union. This
discard sampling programme covered in 1994 the activities of some of
the most important Spanish fleets, trawlers, gillnets, long liners, and
purse seiners, in ICFS Division VIIIc (Pétez etal, 1996).
Recent expansions of the Ecopath approach (Ecosim and Ecospace)
make it possible to simulate changes in fishing pattern and intensity
through time in an ecosystem framework. Ecosim is a time-dynamic
simulation tool for studying fishery policy options (Walters et al, 1997).
Ecosim includes biomass and size structure dynamics: mixed differential and difference equations and use of mass-balance assumptions for parameter estimation. Time patterns of biomass are predicted by these differential equations, and equilibrium system response under different
exploitation regimes. Ecospace is a mesoscale spatial simulation tool for
predicting spatial patterns and runs the Ecopath model through Ecosim
to check the behaviour of ecosystems. Numerical approximation bv
linearisation, and matrix exponential solution method generate projections towards spatial equilibrium. Walters et al. (1998) describe all the
functions used in Ecospace simulations. To explore the simulation capacity of Ecospace, we defined a base-map of the central area of the
Cantabrian Sea with five habitats: oceanic, shelf break, extemal shelf, internal shelf and coastal waters. We also defined the habitat preferences
of different gears and the movement rates and vulnerabilitv in bad habitats of the 25 trophic groups. To test the impact of management
measures, we located the existing restricted area where the use of trawl
gear is forbidden. Subsequendy, we compared the Ecospace and Ecosim
predictions with the results obtained from bottom trawl surveys carried
out before and after the area became restricted in 1992.
Results
The total biomass supported by the ecosystem is estimated at 226 tons
per square kilometre. Big hake and monkfish present the highest trophic
levels (4.6). As refers to the fish species, the EE indicates that 65 to 95% of
the production are used in the system. It also detected some discrepancies
in the natural mortalitv provided by the model with the values used in
the single species analytical assessmcnt methttds (IQIS reports). The M
values for some groups are slightly higher in the Elcopath model than in
thc WA, where they are assumed to have values between 0.2 and 0.8. As an
example, M for blue whiting (the main food intake for hake, monkfish
and big demersal fish in the area) is higher in the model.
In order to compare the relative role of the pelagic, demersal and benthic
subsystems, the figure presents the major biomass flows diagram of the
Cantabrian Sea ecosystem in 1994, estimated bv Ecopath. Most of the
biomass and production are contained within the pelagic domain. The
main flow is determined by the interaction between phytoplankton,
190