An acoustic survey targeting blue whiting (Micromesistius poutassou) spawning and post spawning aggregations in the north east Atlantic in 2005. 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. The acoustic survey programme is carried out for fishery management purposes, results are presented annually at the ICES led Northern Pelagic and Blue Whiting Fisheries Working Group and from this catch advice is determined for the following year. This survey was conducted as part of a collaborative survey coordinated by the Institute of Marine Research, Bergen, Norway, using the vessel the RV “G.O. Sars”. Also participating were the RV Fridtjof Nansen” (PINRO, Russia), RV “Atlantniro” (Russia), RV “Tridens” (RIVO, Netherlands) and the RV “Magnus Heinason” (Faroes). The 2005 survey area extended from the north Porcupine shelf edge as the southern limit, west to the Rockall Bank and northerly extension reached to the Hatton Bank. The Irish component of the survey was made up of transects covering 2,228 nautical miles. To optimise the allotted time a zig-zag transect design was employed. Acoustic data were collected using the Simrad ER60 scientific echosounder. Biological sampling was done using a single pelagic midwater trawl.Fish samples were divided into species composition by weight. Species other than the blue whiting were weighed as a component of the catch. Measurements of blue whiting lengths were taken to the nearest 0.5 cm. Age, length, weight, sex, maturity and stomach fullness data were recorded for 100 blue whiting within a random 150 fish sample from each trawl haul. Visual observations for marine mammals and seabirds were also conducted on the survey. Oceanographic data on temperature, depth and salinity (CTD) were collected at set stations. 1. Collect acoustic data on blue whiting spawning aggregations s of blue whiting (Micromesistius poutassou) along the northern migration pathway 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 surveys of marine mammals and seabirds