Continuous acoustic measurements were conducted using a Simrad EK60 echosounder connected to hull-mounted transducers. These transducers operated at four frequencies: 38, 70, 120, and 200 kHz. For all frequencies, the range was cut at 250 m.

Data acquisition was carried out at an average vessel speed, with an average ping interval tailored to the depths: offshore and in shallower waters. The pulse lengths were set to 512 µs for 38 kHz, 256 µs for 70 kHz, and 128 µs for 120 and 200 kHz. Transmit powers for these frequencies were 1000 W, 700 W, 200 W, and 90 W, respectively.

The near-field noise was removed (10 m, 13 m, 10 m, 10 m deep from the surface  respectively) from the analysis; phantom bottom echoes were excluded and the bottom line was corrected manually. The acoustic nautical area scattering coefficient (sA in m2 nmi-2 or 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 onto 1 m high layers over 0.05 nmi ESDU (elementary sampling distance unit) with a -100 dB threshold, from 10 m down to 250 m depth. The data provided are the results of the echointegration processing.