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The main aim of present study was to analyze the spatial and temporal trends segregation by sex of blue shark (Prionace glauca) in the Eastern Atlantic and Western Mediterranean Sea from the individual bycatches by Spanish surface longline fleet. Our results indicate significant differences in the use of space between males and females. Thus, in low latitudes, within the observed range, sharks are mixed, but from North 38 degree of latitude tend to segregate. In the case of length, a similar pattern is observed, in low longitude sexes appear overlapped, and while to high longitude tend to appear segregated. All these results suggested segregation by sex in the Mediterranean where sharks are grouped in single-sex schools.

The Mediterranean Sea is considered by several authors as a hot-spot of Climate Oscillation, such as the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). However, information about the effect of the climate oscillations on the fitness of the species is still scarce. In this context, bullet tuna is an important migratory species with a substantial socio-economical value, whose fisheries might be affected by the effect of certain climatological conditions. In fact, these atmospheric oscillations trigger a chain of hydrodynamic events, leading a change on the timing, destinations, and success of the migratory species in their search for spawning grounds. This study relies on the hypothesis of a correlation between the physical condition of the post-spawning bullet tuna and climate oscillation indexes. For that purpose, 151 individuals of bullet tuna, Auxis rochei, were collected in the traps of Ceuta (Alboran Sea) during three different years, (1983, 1984 and 2014). The physical condition index was calculated, and later statistically correlated with the climate oscillation indexes proposed. Significant differences were found between the physical condition of A. rochei and the average accumulated NAO index. Moreover, for age class 3+ we obtained a significant correlation with atmospheric oscillations.

Pelagic migrating sharks are by-caught incidentally in longline fisheries. Some of these species have been catalogued as threatened or vulnerable by several Regional Fisheries Organizations and International Conservational NGOs. Alboran Sea is an important area for pelagic migrating sharks because it is the natural and unique communication way between the Atlantic Ocean and Mediterranean Sea. This area is considered by several authors as a hot-spot of Climate Oscillation, such as the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). In addition, Alboran Sea is an important fishing ground where the longline fisheries targeting swordfish operates. Recent studies concluded that historical landing of pelagic sharks from harbours of Alboran Sea and Balearic Sea were mediated for atmospheric oscillations. The main aim of the present study was to assess the effect of atmospheric oscillation on the Catch per Unit Effort (CPUE) of vulnerable sharks thresher shark, Alopias vulpinus (Bonnaterre, 1788) and shortfin mako, Isurus oxyrinchus (Rafinesque, 1810) by-caught in the traditional longline fisheries. The atmospheric oscillations tested in this study were the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). We found a significant positive correlation between the NAO and AO indexes of the previous year to the CPUE tested.

The main aim of present study was to analyze the spatial and temporal trends segregation by sex of blue shark (Prionace glauca) in the Eastern Atlantic and Western Mediterranean Sea from the individual bycatches by Spanish surface longline fleet. Our results indicate significant differences in the use of space between males and females. Thus, in low latitudes, within the observed range, sharks are mixed, but from North 38 degree of latitude tend to segregate. In the case of length, a similar pattern is observed, in low longitude sexes appear overlapped, and while to high longitude tend to appear segregated. All these results suggested segregation by sex in the Mediterranean where sharks are grouped in single-sex schools.

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Food and feeding of the 15 fish species taken by bottom trawl from Flemish Cap Bank in summer during the period 2001-2003 were analysed. The stomach contents of 17 773 fish were collected in depths from 83 to 730 m. In general, the feeding intensity was high in all the species with a maximum value for Gadus morhua (96.3%) and minimum for Lycodes reticulatus (35.0%). The prey spectrum was width, with a total of 134 items for all the stomachs analysed. In frequency of occurrence, the crustaceans were the most important preys (FO = 80.4%), while in volume (V = 39.4%) they were less significant than fishes (V = 43.5%). The main prey group in frequency of occurrence were Hyperiidea, Copepoda, Pandalus borealis and Chaetognata. The niche width index was also calculated for these species.