Over the French shelf, between Capbreton and the coasts of Brittany, the
state of water masses is directly related to tidal action, wind effect and
freshwater supplies. Lastly, over the Celtic Sea area, the surface salinity
pattem is mainly driven by the budget between rainfall-evaporation and the
incoming fluxes.
Material and methods
During the autumn (from September to November) of 1997 and 1998,
two series of bottom trawl surveys were conducted. In both years, the
European Atlantic shelf from Southem Ireland to the North of Portugal
was sampled. All the area was stratified according to geographical sectors
and depth strata (K .liS, 1999; SF.SITS, 2000). In the French area the surveys were conducted with the R/V ‘'ïhalassa”using the GOV trawl gear.
A total of 130 and 126 valid hauls were carried out in the 1997 and 1998
surveys respectively. In the Spanish area, the surveys were performed
vdth the R/V “Comide de Saavedra" using the baka trawl gear. A total of
116 and 114 valid hauls during the 1997 and 1998 survevs were respectively performed. The indices obtained from 7'Mœa-GOV were transformed
into Comide-lidka. indices using conversion coefficients obtained from overlapping experiments (ICHS, 1999).
The hydrographical observations were performed over 309 and 429 CTD
stations each year respectively, patred to the majority of the fishing hauls
over the shelf and some extra-stations in cross-slope radial profiles. An
objective analysis technique, as described by Gil (1995), was applied to
construct the totai field of temperature, salintty
7 and dynamic topography
at different depths.
Results
In the studied area two species of megrims, the four-spot megrim (/ xpidorhomhus hoscii) and tlre megrim (7_ whiffiagonis), cohabited. The four-spot
megrim shows a preference for southem regions while the megrim is
mainly associated to northem waters being the bay of Biscay, and particularly the (iantabrian Sea, the overlapping area of the distribution of both
species. Megrim was more abundant in the Celtic Sea, where bottom temperatures were driven by the cold cyclones over the shelf, whereas the fourspot megrim was more abundant in the Cantabrian Sea, associated with the
occurrence of warmer temperatures. In the Celtic Sea, the bottom temperature distribution pattem appears reversed. Temperature is lower in the
shallower regions of the Celtic Sea than m areas situated near the shelf
break. Tlais particular thermohaline distribution has driven the four-spot
megrim locution in this northern area (fig. 1).
174
state of water masses is directly related to tidal action, wind effect and
freshwater supplies. Lastly, over the Celtic Sea area, the surface salinity
pattem is mainly driven by the budget between rainfall-evaporation and the
incoming fluxes.
Material and methods
During the autumn (from September to November) of 1997 and 1998,
two series of bottom trawl surveys were conducted. In both years, the
European Atlantic shelf from Southem Ireland to the North of Portugal
was sampled. All the area was stratified according to geographical sectors
and depth strata (K .liS, 1999; SF.SITS, 2000). In the French area the surveys were conducted with the R/V ‘'ïhalassa”using the GOV trawl gear.
A total of 130 and 126 valid hauls were carried out in the 1997 and 1998
surveys respectively. In the Spanish area, the surveys were performed
vdth the R/V “Comide de Saavedra" using the baka trawl gear. A total of
116 and 114 valid hauls during the 1997 and 1998 survevs were respectively performed. The indices obtained from 7'Mœa-GOV were transformed
into Comide-lidka. indices using conversion coefficients obtained from overlapping experiments (ICHS, 1999).
The hydrographical observations were performed over 309 and 429 CTD
stations each year respectively, patred to the majority of the fishing hauls
over the shelf and some extra-stations in cross-slope radial profiles. An
objective analysis technique, as described by Gil (1995), was applied to
construct the totai field of temperature, salintty
7 and dynamic topography
at different depths.
Results
In the studied area two species of megrims, the four-spot megrim (/ xpidorhomhus hoscii) and tlre megrim (7_ whiffiagonis), cohabited. The four-spot
megrim shows a preference for southem regions while the megrim is
mainly associated to northem waters being the bay of Biscay, and particularly the (iantabrian Sea, the overlapping area of the distribution of both
species. Megrim was more abundant in the Celtic Sea, where bottom temperatures were driven by the cold cyclones over the shelf, whereas the fourspot megrim was more abundant in the Cantabrian Sea, associated with the
occurrence of warmer temperatures. In the Celtic Sea, the bottom temperature distribution pattem appears reversed. Temperature is lower in the
shallower regions of the Celtic Sea than m areas situated near the shelf
break. Tlais particular thermohaline distribution has driven the four-spot
megrim locution in this northern area (fig. 1).
174