This survey was conducted by the Marine Institute on-board the RV Celtic Explorer in summer 2013 as part of the North West Herring Acoustic Survey. The northwest and west coast (ICES Divisions VIaS and VIIb) herring acoustic survey programme was first established in 1994. The summer 2013 survey represents the sixth in the new time series, starting in 2008. The survey was coordinated through the ICES Working Group of International Pelagic Surveys (WGIPS). Survey data on stock numbers at age are submitted to the ICES Herring Assessment Working Group (HAWG) and used in the annual stock assessment process. The northwest and west coast (ICES Divisions VIaS and VIIb) herring stock is composed of two spawning components, autumn and winter spawners. Spawning covers a large geographical area and extends over a 4-month period from late September through to late March. Traditionally, fishing effort has been concentrated on spawning and pre-spawning aggregations. The autumn spawning component, which mostly occurs within VIIb and VIaS, feeds along the shelf break area to the west of the spawning grounds. The winter spawning component is found further north in VIaS. In VIaS, summer distribution extends from close inshore to the shelf break. Components of the winter spawning fish are known to undertake northward feeding migration into VIaN before returning in the winter to spawn along the Irish coast. This survey, carried out between 22nd June and 12th July, focused on the northwest and west coast of Ireland and the west coast of Scotland. The survey track started to the southeast of the Isle of Coll, zigzagged north through the Minches (between the Scottish mainland and the Hebrides), then worked progressively southwards in parallel eastwest transects, and finished near the mouth of Killary Harbour. A systematic parallel transect design was adopted for the majority of the survey, with a randomised start point. Transects were positioned running perpendicular to the lines of bathymetry where possible. To keep in line with existing survey methodology acoustic data collection was only undertaken during daylight hours (04:00 and 00:00). The acoustic data were collected using the Simrad ER60 scientific echosounder. For biological sampling, a single pelagic midwater trawl was used. 22 hauls were carried out. All components of the catch from the trawl hauls were sorted and weighed; fish and other taxa were identified to species level. Oceanographic stations were carried out during the survey at predetermined locations along the track. A marine mammal observer was also present to conduct visual surveys of marine mammals and seabirds.. The aim of the acoustic survey is to determine the relative abundance of the target species, herring. This information is then used to determine catch rates and management advice for the following year. Other objectives include collecting physical oceanography (CTD) data and visual surveys for marine mammals and seabirds. Acoustic and biological data on boarfish (Capros aper) was also collected for the Boarfish Acoustic Survey, 2013.