The MSS deepwater trawl survey is a time series from the continental slope of the Rockall Trough, NE Atlantic. The survey covers depths between 300-2067m. The survey began in 1998 and has taken place each year except 1999, 2001, 2003, and 2010. The bottom trawl samples the demersal fish living on or near the sea bottom (fish that live in the water column are excluded). All fish species are identified and recorded. A total weight and number of individuals for each species is recorded. Length frequency data is collected from a representative sample of each species. This dataset is a summary of the main database and comprises information on total number and weight per hour of trawling for each species for each year. NperHr = number of individuals caught per hour of trawling, averaged across hauls in a year. KgperHr = biomass of individuals caught per hour of trawling (in kg), averaged across hauls in a year. SpeciesCode = a three letter Marine Scotland reference code. This data set was used in the publication written in collaboration with University of Sheffield ‘Mindel et al. 2015. A trait-based metric sheds new light on the nature of the body size–depth relationship in the deep sea. J. Anim. Ecol. (online: doi: 10.1111/1365-2656.12471).