Hydroacoustic data EK60 Greenland Sea August-September 2017

Hydroacoustic data were collected in the Greenland Sea from 22 August to 12 September 2017, onboard RV Dana. The Simrad® EK60 split-beam echosounder with hull-mounted transducers at 18kHz, 38 kHz and 120 kHz recorded data continuously during the cruise, except during the deployment of the WBAT. Acoustic data from the EK60 were analyzed following Bouchard et al. (2017). CTD (conductivity-temperature-depth) profiles were used to determine sound speed in water and the coefficient of sound absorption for the acoustic analysis. Echograms were scrutinized to discard noise. The difference in mean volume backscattering strength (ΔMVBS) at 38 and 120 kHz (ΔMVBS120–38) was then used to isolate the signal of fish in echo-integration cells of 5 minutes long by 5 m deep between 14.5 m and 100 m. Only cells with ΔMVBS120–38 ranging from -10 to 5 dB re 1 m-1 were kept for further analyses. Backscatter profiles of fish were then converted into density profiles (ind. m-3) and we assumed that most of the fish signal originated from ichthyoplankton because older stages of the fish species present remain close to the bottom at this time of the year. Bouchard, C, Geoffroy, M, LeBlanc, M, Majewski, A, Gauthier, S, Walkusz, W, Reist, JD and Fortier, L. 2017. Climate warming enhances polar cod recruitment, at least transiently. Prog Oceanogr 156(Supplement C): 121-129. DOI:https://10.1016/j.pocean.2017.06.008.