In the southwest of Ireland and the Celtic Sea (ICES divisions: 7j-g and 7aS), herring are an important commercial species to the pelagic and polyvalent fleet. Acoustic surveys are currently are the only tuning indices available for this stock. Since 2004 the survey has been fixed in October and carried out onboard the RV Celtic Explorer. During this 21 day survey in the Celtic Sea acoustic data were collected using the Simrad EK60 scientific echosounder. Biological sampling was carried out at 17 stations using a pelagic midwater trawl with all components of the catch from the trawl hauls sorted and weighed; fish and other taxa were identified to species level. In additional hydrographic data on temperature, depth and salinity were collected using a calibrated Seabird 911 sampler and 17 grab samples obtained. Marine mammal and seabird surveys were also conducted.