Understanding the relationship between habitat and fish distribution is a central component in the recent shift towards ecosystem based fisheries management(EBFM). Determining the habitat requirements of commercially and ecologically important species will be essential if spatial management strategies such as marine protected areas (MPAs) are to be used successfully to conserve marine resources. Areview of demersal fish habitat research highlighted numerous areas lackingin this field of habitat science. These included the propensity for studiesto focus on abiotic habitat variables such as depth and sediment over large spatial scales(≥ 100s km2)and the low number of studies analysing biotic habitat variables in general. I concludethat development of sound predictive science in this field is reliant on a change in research focustoward reductions in study scale, or increases in resolution for abiotic habitat variables and more integration of biotic variables into studies. The three field studies included in this thesis analyse the importance of prey resource forthe distribution of demersal fishes over spatial scales ranging from hundreds of metres to tens of kilometres. The first study investigates the relationshipbetween prey and predator abundance and prey size and predator mouth gape size for nine demersal fish speciesaround the Balearic Islands in the Mediterranean. The results demonstrate that prey abundance and size are of significance for some demersal fish species feeding primarily on benthos and will help in defining habitat requirements of demersal fish species. Demersal fish feeding ecology is studied in more depth when I investigate the effects of a bottom trawl fishery on an invertebrate benthic community and the subsequent effects this has on two commercially important flatfishes (P. platessaand L. limanda). This chapter closes the gap between the effects of bottom fishing on benthic communities and the reduced condition of some fishes found within these areas. Theresults of this study suggest that alterations in prey abundances, sizes and availabilities caused by chronic bottom trawling may lead to reducedfeeding efficiencies, particularly for species with narrow prey spectrums. This in turn could result in reduced conditions of affected fishes living in chronically disturbed areas.The final data chapter uses detailed habitat maps, based on differences in sediment characteristics between three sites to take a small spatial scale, high resolution approach to describing demersal fish habitat. This investigates changes in the feeding ecology of a demersal fish species, Callionymus lyra, withbody length. Although significant differences in prey size and prey taxa selectivity were found, no significant relationships between prey resource and predator distribution were apparent for any of the year classes analysed. The potential ecological and methodological reasons for these findings are discussed in-depth. Finally, a general discussion examines the main findings and suggests areas for future development.