Continuous acoustic measurements were made with calibrated echosounders (Foote et al., 1987) Simrad EK80 connected to hull-mounted (6m below the waterline) transducers operating at five frequencies: 18, 38, 70, 120, 200 and 333 kHz. Data were acquired at a typical vessel speed of 8 knots with an average ping interval of 6 s. The pulse length was set at 1024 µs for all frequencies and transmit powers were of  1600, 2000, 600, 200, 90 and 40 W for the four channels at 18, 38, 70, 120, 200 and 333 kHz, respectively. The water column was sampled down to depths of 1500, 1500, 600, 300, 150 and 100 m, respectively for those channels.

Acoustic data were scrutinized, corrected and analysed using the “Movies3D” software developed at the “Institut Français de Recherche pour l'Exploitation de la Mer” (Ifremer; Trenkel et al., 2009) combined with the French “Institut de Recherche pour le Développement” (IRD) open source tool “Matecho” (Perrot et al., 2018), developed in MATLAB.

The near-field noise was removed from the analysis; phantom bottom echoes were excluded and the bottom line was corrected manually. Echograms were cleaned by eliminating unwanted signals such as one impulsive noise, transient noise due to the interferences with other electronic devices or other sources. Background noise was estimated and subtracted using methods described by De Robertis and Higginbottom (2007). Echograms were scrutinized and manually cleaned. The acoustic nautical area scattering coefficient (NASC), an indicator of marine organisms biomass, and the acoustic volume backscattering strength (Sv in dB re 1m-1), an indicator of marine organisms density, were calculated. Data were echo-integrated at 5 m high layers over 0.1 nmi ESDU (elementary sampling distance unit) and  with a -80 dB threshold, from 8 m down to 1500 m depth. The data provided are the results of the echointegration processing.

Sensors metadata and variables are described in the report "ICES. 2016. A metadata convention for processed acoustic data from active acoustic systems. Series of ICES Survey Protocols SISP 4-TG-AcMeta. 48 pp".