An acoustic survey targeting blue whiting (Micromesistius poutassou) spawning and post spawning aggregations in the north east Atlantic in 2015. Spawning takes place from January through to April along the shelf edge from the southern Porcupine Bank area northwards to the Faroe/Shetland Ridge including offshore areas as the Rosemary, Hatton and Rockall Banks. Peak spawning occurs between mid-March and mid April and acoustic surveys are timed to occur during this phase. To facilitate a more coordinated spatio-temporal approach to the survey participating countries meet annually to discuss survey methods and define effort allocation at the ICES led Working Group International Pelagic Surveys (WGIPS). The survey covered the core spawning area of blue whiting to the west of Scotland and the Western Isles. Coverage extended from the shelf slopes (250m) westward into the Rockall Trough. The survey was carried out in continuity from north to south and from south to north The 2015 survey was part of an international collaborative survey using the vessels RV Celtic Explorer (Ireland), FV Fridtjof Nansen (Russia), RV Tridens (Netherlands) and the RV Magnus Heinason (Faroes). Transect design and effort allocation was pre-agreed for each vessel. A parallel transect design was used to allow transect interlacing in co-surveyed target areas (east-west orientation). Acoustic data were collected using the Simrad ER60 scientific echosounder. Cruising speed was maintained at a maximum of 10 Kts (knots) where possible. Biological sampling was done using a single pelagic midwater trawl. All components of the catch from the trawl hauls were sorted and weighed; fish and other taxa were identified to species level. Age, length, weight, sex, stomach fullness and maturity data were recorded for individual blue whiting within a random 50 fish sample from each trawl haul with a further 100 random length and weight measurements were also taken. All blue whiting were aged onboard. Visual observations for cetaceans were conducted during daylight hours. Passive Acoustic Monitoring (PAM) for cetaceans was also conducted using a towed hydrophone array which was towed 150m behind the vessel. Seabird surveys were also carried out. Oceanographic data on temperature, depth and salinity (CTD) were collected at set stations. 1. Collect acoustic data on blue whiting spawning aggregations 2. Collect biological samples from directed trawling on fish echotraces to determine age structure and maturity state of survey stock 3. Collect CTD data 4. Conduct visual abundance surveys of marine mammals and seabirds in conjunction with passive acoustic monitoring of marine mammals