Leg four of the 2017 Irish Anglerfish and Megrim Survey (IAMS) took place from 8-17th April 2017 on RV Celtic Explorer in the North East Atlantic (International Council for the Exploration of the Sea (ICES) area 6a). Regions 6a and 7 are treated separately because they are comprise different assessment and Total Allowable Catch (TAC) areas. The survey was conducted in order to obtain biomass estimates for anglerfish (Lophius piscatorius and L. budegassa) and establish an abundance index for megrim (Lepidorhombus whiffiaginis and L. boscii). The IAMS survey is coordinated with the Scottish Anglerfish and Megrim Survey (SIAMISS) and uses the same gear and fishing practices. For this survey, sampling stations were selected at random. The gear, based on a standard commercial otter trawl, was trawled at 3kn for one hour at each station. All fish and invertebrate species were sorted and weighed. Biological data recorded on fish species include sex, maturity and age. The main objective of the survey is to obtain biomass estimates for anglerfish (Lophius piscatorius and L. budegassa) and establish an abundance index for megrim (Lepidorhombus whiffiaginis and L. boscii) in ICES areas 6a (south of 58°N) and 7 (west of 8°W). Secondary objectives are to collect data on the distribution and relative abundance of anglerfish, megrim and other commercially exploited species. The survey also collects maturity and other biological information for commercial fish species.