Sound scattering layers (SSLs) are observed over a broad range of spatio-temporal scales and geographical areas. SSLs represent a large biomass, likely involved in the biological carbon pump and the structure of marine trophic webs. Yet, the taxonomic composition remains largely unknown for many SSLs. To investigate the challenges of SSL sampling, we performed a survey in a small study area in the Northern Bay of Biscay (France) by combining broadband and narrowband acoustics, net sampling, imagery and video recordings. In order to identify organisms contributing to the observed SSLs, we compared measured frequency spectra to forward predicted spectra derived from biological data. This dataset comprises the echo-integrated broadband acoustic data (in Sv(f)), the nets position and depth, and the abundance and the size of the catched organisms acquired during a specific operation of SSLs sampling during (Blanluet et al.)-[https://doi.org/10.1371/journal.pone.0223618]. Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

These data consist of raw uncalibrated 38 and 120 kHz echosounder observations collected during a pelagic survey of the Chagos archipelago MPA (January 2015). Observations were collected from a pole-mounted system (transducers were fixed at a depth of 3m). Data include several transects recorded during the 19th January at the Swart seamount site (close to Diego Garcia). A calibration was conducted prior to the survey. Resultant transducer peak gain (G0) and Simrad correction factor (Sa) values were as follows: 38 kHz (power = 1000 W; pulse duration = 1.024 ms; G0 = 20.97 dB; Sa = -0.62 dB) and 120 kHz (power = 250 W; pulse duration = 1.024 ms; G0 = 24.5 dB; Sa = -0.29 dB).