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Fisheries acoustic surveys are routinely conducted around the world, and particularly within the ICES community. For nearly 20 years, the Simrad EK60 system has been the most commonly used echosounder equipment, and it is now being superseded by the Simrad EK80 system (CW mode). The comparison of the two systems and the impact of the transition from one system to the next for routine acoustic surveys has been investigated by several institutes. This report specifically investigates the use of the EK80 CW on board the Dutch Research Vessel (RV) Tridens II. RV Tridens II is routinely used by Wageningen Marine Research for conducting acoustic surveys. Currently, while the EK80 system is also available on board, the EK60 is used for survey recordings. In order to bring a transition from the EK60 to the EK80 CW, this study investigated: 1. the consistency in calibration results for the EK80 CW since 2015. This is done by generating time series plots of historical EK80 CW calibration data collected on RV Tridens II. 2. the consistency between the EK60 and the EK80 CW with data collected ping to ping using a multiplexer during the herring acoustic surveys (HERAS) in 2017 and 2018. The EK60/EK80 CW results are also put in light of findings of another published study (Macaulay et al. 2018) based on data collected on RV Tridens II in 2016 during the blue whiting acoustic (IBWSS) survey. Calibration and EK60/EK80 CW results from HERAS 2018 reveal large discrepancies with the EK80 CW 38 kHz channel originating from July 2017. The EK60/EK80 CW results from HERAS 2018 also show smaller discrepancies for the 18 kHz channel, due to different areas of the acoustic ring down below the transducer and noise interferences of the EK80 CW. Nevertheless, the analysis of other frequency channels for both HERAS 2017 and 2018 data show a good agreement between the systems. In addition, the analysis of 18 kHz and 38 kHz channels for HERAS 2017 exemplify good consistency between the EK60 and the EK80 CW, suggesting an electrical problem is causing the discrepancies observed during HERAS 2018. Though the issue with the 18 kHz and 38 kHz channels on board RV Tridens II needs to be tackled prior to using the EK80 CW for routine surveys, this study together with previous studies suggest that results from the EK80 CW are comparable to those of the EK60. It is therefore recommended to switch to using the EK80 CW for routine acoustic surveys onboard RV Tridens II once the issue with the equipment malfunctioning is resolved.

Investigation of the use of the EK80 CW during acoustic surveys on board Tridens