Every three years the International Council for the Exploration of the Sea (ICES) coordinates a series of mackerel and horse mackerel egg surveys covering the eastern Atlantic from Gibraltar to the north coast of Scotland between January and July. The aim of this survey programme is to assess the northeastern Atlantic mackerel and horse mackerel stock. The Marine Institute participates in this programme and covers stations in the Celtic Sea. The survey was carried out in July/August2013. Plankton samples were collected at set stations, fishing hauls were made to collect mackerel and horse mackerel samples for fecundity analysis. Samples were collected to ensure maximum temporal and geographical spread. The aim of the international Mackerel and horse mackerel egg survey program was to estimate the spawning stock biomass (the total weight of all sexually mature fish in the population) of the North-east Atlantic mackerel and horse mackerel stocks.