The purpose of this benthic survey (cruise 1621A) in the approaches to the Sound of Mull and northern part of the Firth of Lorn was to improve knowledge of the occurrence and distribution of species and habitats of recognised conservation importance, particularly priority marine features (PMFs), because this area is one of the sites of interest to the development of marine renewables. The possible routing of subsea cables from Tiree via the Sound of Mull and Firth of Lorn was proposed at the time of this survey. A further aim was to assess the implications of this planned development on the features of importance. An underwater video survey were conducted by MSS for MSS on the 29-30th September 2012 to collect detailed biological information on the seabed species and habitat features present. Drop-down video drift tows were undertaken at 36 sites. Analyses on the seabed video and still photographic imagery, commissioned by SNH, were used to describe the nature of the seabed in terms of the physical structure and the species assemblages. MSS used the vessel FRV Alba na Mara for this survey.