and have a medium trophic level (3.56). Gillnets exploit certain predators from the demcrsal domain as well as from the benthic, and present
a high trophic level (4.23). It is possible to observe, in the figure the flow
of discards (2.07 t/km
2 per year) in the model. The groups mainly favoured are those of the benthic domain, and especially benthic invertebrate carnivores, benthic fish and dogfish. The importance of discards
as food in the ecosystem is low and constitutes only 0.014% of the total
intake.
Simulation and projections with Ecosim, with different trawl fishing regimes starting from the present, using mixed trophic control between the
“top-down” and “bottom-up” strategic trctphic alternatives ht'potheses, are
implemented. For wider ranges of F the basic Fcosim output is a graphical displav of the relationship between equilibrium biomasses, catch and
fishing rates. Rays and dogfish (large-bodied species with low rates of
turnover), monkfish, megrim (only traw) catch), hake (strong trawl effect
on juveniles), benthic Cephalopoda and big demersal fish are the main
trophic groups; the\- increase their biomasses when the trawl fishing regime decreases. Mackerel, small demersal fish and small pelagic (populations with high rates of turnover) are not affected by the different values
of trawl regime. In addition, the scavenging species, as benthic in\'ertebrate carnivores, are not affected by different trawl regime.
A 30-years Fcosim simulation with trawl fishing regime equal to 0 is
used to predict the recovery period of species affected by a trawl closed
area. For most of the aftected species (rav, dogfish, monkfish and megrims) 20 years are necessaty (more for ravs) to reach the biomass equilibrium. ITe consequences for the rest of the species are scarce, but it is
obvious that the model has not considered other important etfects of
trawl, such as habitat changes for example. The increment in biomass for
the four favoured species in these 30 \ ears has limited repercussions on
the economy of the fisherv sector. Ravs and dogfish have low commercial value and megrim is only accessible with trawl, a gear supposed to
have disappeared from the area. Only gillnet would beneflt from the increase in monkfish biomass, since this species cannot be caught with
other gears.
Fcospace predictions of steady-state biomass densitics in the base-map
of the central Cantabrian Sea during a five-years simulation, including the
effects of trawling restriction, show that in the restricted area the biomass
levels of rays, dogfish, monkfish and benthic cephalopods are bigger than
in adjacent areas. Also, trawl exclusion in this area reduces the biomass
of benthic invcrtebrate carnivores (more pressure of predators) and
shows low values of discards. To validate the results of this simulation,
we use the abundance indices from bottom trawl survet s carried out
during a number of years before and after the closure of an area (Llanes
area, central Cantabrian Sea). dhe indices show that the biomass of all the
groups considered are bigger after restriction. Dogfish, rays, big demersal
fish and benthic fish are the main beneficiaries. Tlte main discrepancy
192
a high trophic level (4.23). It is possible to observe, in the figure the flow
of discards (2.07 t/km
2 per year) in the model. The groups mainly favoured are those of the benthic domain, and especially benthic invertebrate carnivores, benthic fish and dogfish. The importance of discards
as food in the ecosystem is low and constitutes only 0.014% of the total
intake.
Simulation and projections with Ecosim, with different trawl fishing regimes starting from the present, using mixed trophic control between the
“top-down” and “bottom-up” strategic trctphic alternatives ht'potheses, are
implemented. For wider ranges of F the basic Fcosim output is a graphical displav of the relationship between equilibrium biomasses, catch and
fishing rates. Rays and dogfish (large-bodied species with low rates of
turnover), monkfish, megrim (only traw) catch), hake (strong trawl effect
on juveniles), benthic Cephalopoda and big demersal fish are the main
trophic groups; the\- increase their biomasses when the trawl fishing regime decreases. Mackerel, small demersal fish and small pelagic (populations with high rates of turnover) are not affected by the different values
of trawl regime. In addition, the scavenging species, as benthic in\'ertebrate carnivores, are not affected by different trawl regime.
A 30-years Fcosim simulation with trawl fishing regime equal to 0 is
used to predict the recovery period of species affected by a trawl closed
area. For most of the aftected species (rav, dogfish, monkfish and megrims) 20 years are necessaty (more for ravs) to reach the biomass equilibrium. ITe consequences for the rest of the species are scarce, but it is
obvious that the model has not considered other important etfects of
trawl, such as habitat changes for example. The increment in biomass for
the four favoured species in these 30 \ ears has limited repercussions on
the economy of the fisherv sector. Ravs and dogfish have low commercial value and megrim is only accessible with trawl, a gear supposed to
have disappeared from the area. Only gillnet would beneflt from the increase in monkfish biomass, since this species cannot be caught with
other gears.
Fcospace predictions of steady-state biomass densitics in the base-map
of the central Cantabrian Sea during a five-years simulation, including the
effects of trawling restriction, show that in the restricted area the biomass
levels of rays, dogfish, monkfish and benthic cephalopods are bigger than
in adjacent areas. Also, trawl exclusion in this area reduces the biomass
of benthic invcrtebrate carnivores (more pressure of predators) and
shows low values of discards. To validate the results of this simulation,
we use the abundance indices from bottom trawl survet s carried out
during a number of years before and after the closure of an area (Llanes
area, central Cantabrian Sea). dhe indices show that the biomass of all the
groups considered are bigger after restriction. Dogfish, rays, big demersal
fish and benthic fish are the main beneficiaries. Tlte main discrepancy
192