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.

Food resource partitioning and some trends in the feeding ecology of 13 species of fishes inhabiting the slope of the Catalan Sea (western Mediterranean) were examined. Specimens were collected from 1987 to 1991, using bottom trawls at depths between 1000 and 2250 m. Prey selection was also examined in relation to data collected in the same area on 2 potential prey compartments for fish, the benthopelagic macrofauna -suprabenthos or hyperbenthos -and the megafaunal decapod crustaceans. Thus, the possible connections with prey availability within the benthic boundary layer (BBL) were also analysed. The size of available food resources was the most important factor responsible for food resource partitioning, both by depth stratum and season. The importance of the variable predator size is also evidenced. Most of the deep-sea demersal fish species inhabiting the CatalanoBalearic slope often consumed a variety of available resources in their diets, mainly comprising suprabenthos, but also infauna or planktonic prey. Thus, the BBL macrofauna constitute an important part of the available food exploited, with the range of the prey consumed increasing for the largest predators. A significant trend to increase dietary H ' values within the depth interval where each species attained its maximum abundance was observed. Some (positive) prey selection upon certain prey groups was detected depending on the fish species: sharks, Alepocephalus rostratus and Nettastoma melanurum preferentially preyed on decapods, siphonophores and pyrosomids; Polyacanthonotus rissoanus, macrourids, Lepidion lepidion and Cataetyx alleni preyed upon suprabenthic peracarid crustaceans; and only Bathypterois mediterraneus preferentially consumed copepods, the numerically dominant group in the bathyal BBL.

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