The Pélagiques Gascogne (PELGAS, Doray et al., 2000) integrated survey aims at assessing the biomass of small pelagic fish and monitoring and studying the dynamics and diversity of the Bay of Biscay pelagic ecosystem in springtime. PELGAS has been conducted within the EU Common Fisheries Policy Data Collection Framework and Ifremer’s Fisheries Information System. Details on survey protocols and data processing methodologies can be found in Doray et al., (2014, 2017a). This dataset comprises the biomass (in metric tons) and abundance (in thousands of individuals) at length (in cm) of small pelagic fish estimated during the PELGAS survey in the Bay of Biscay in springtime. Total biomass and abundance per species on one hand, and frequencies-at-lenght per species and acoustic Elementary Distance Sampling Units (EDSUs) on the other hand, have been derived from fisheries acoustic and midwater trawl data based on the methodology described in Doray et al. (2010). Frequencies-at-lenght per species and EDSUs have been averaged over the survey area for each species and multiplied by the total biomass and abundance per species, to derive global biomass and abundance at length estimates. This dataset was used in Doray et al., 2017b.