An acoustic survey targeting blue whiting (Micromesistius poutassou) spawning and post spawning aggregations in the north east Atlantic from 22nd March to 11th April 2012. 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 2012 survey covered the core spawning area of blue whiting to the west of Scotland and the Western Isles. Coverage extended from the shelf slopes (250 m) westward to the western flanks of the Rockall Bank. The survey was part of an international collaborative survey using the vessels RV Celtic Explorer (Ireland), RV Fridtjof Nansen (Russia), RV Tridens (Netherlands) and the RV Magnus Heinason (Faroes) and the FV Brennholm (Norway). 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 mid-water trawl. All components of the catch from the trawl hauls were sorted and weighed; fish and other taxa were identified to species level. 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