Diets and bathymetric distributions of two bathyal sharks of the Catalan deep sea (western Mediterranean)

Abstract

Bathymetric distribution of Centroscymnus coelolepis has been studied. This species was restricted to the lower slope (1419 to 2251 m), where it was the only dbundant shark. Galeus rnelastornus was abundant below 1000 m but became rare between 1400 dnd 1600 m, so that there is almost no bathymetric overlap with C. coelolepis. Greatest abundance of G. melastomus in the Catalan Sea was found in the upper slope. Diets of both species showed a very low overlap which is mainly attributed to the dietary specialization of C. coelolepis. Its diet is almost exclusively based on cephalopods. The diet of G. melastomus has been analyzed at depths below 1000 m. Its diet is more diverse than that of C. coelolepis and cephalopods are not preferential prey. The upper and middle slope specimens of G. melastomus have a different diet; this difference may be the consequence of a change in available resources. Finally the trophic position of Etrnopterus spinax, the third most abundant shark below 1000 m, seems to be more similar to that of C. coelolepis. These results suggest that a possible competition is more likely between C. coelolepis and E. spinax than between C. coelolepis and G. melastomus. This could explain the bathymetric displacement of C. coelolepis in the western Mediterranean as a result of an interaction between species of higher trophic levels.