This survey took place onboard the R/V Celtic Explorer on behalf of the MESH (Mapping European Seabed Habitats) European Union INTERREG IIIb project. The cruise took place between the 4th and 18th of June 2007. The study area is located 320km to the southwest of Land’s End . The area surveyed comprises continental shelf sloping south-westwards to the shelfbreak which occurs at a depth of approximately 200m. From there it passes down to the much steeper, deeply incised (canyoned) continental slope. The area surveyed includes two canyons and the eastern flank of a third canyon, straddling the UK/Irish median line. Due to the constraints of the multibeam system used for this survey, no data could be collected in water depths greater than 1165m. The objectives of the R/V Celtic Explorer cruise were to collect high-resolution bathymetry, backscatter, sub-bottom and camera data from the submarine canyons located in the South West Approaches. These canyons were being investigated to confirm the presence of habitats listed in Annex I of the EC Habitats Directive 92/43/EEC (EC, 1992), in particular Annex I reef habitat and to test the application of the MESH Guidance framework for seabed habitat mapping, covering all stages of a project from planning through survey, analysis, map production and finally the practical application of maps for environmental management.