The SEAT algorithm aims at classifying different fish species using relative frequency response acquired by downward looking echosounders operating at multiple frequencies. The performance of the system has been being evaluated on three Dutch freezer trawlers: Fishing Vessel (FV) SCH302 Willem van der Zwan, FV SCH6 Alida and FV SCH24 Afrika. One of these vessels (FV Alida SCH6) operates a mixture of SIMRAD EK60 & EK80 software while others operate only Simrad EK80. As reported by these vessels, the classification accuracy of the SEAT software has been reduced particularly at the later stages of the project. To investigate this problem these vessels collected acoustic data in close range of each other while targeting herring in the summer of 2017 at east of Shetland isles. Using this dataset together with calibration data, a statistical comparison was conducted. Furthermore, potential discrepancies between Simrad EK60 and EK80 systems were examined using data collected during herring assessment survey HERAS of Fishing Research Vessel (FRV) TRIDENS in July 2017. This dataset included recordings of both systems in alternating mode enabling a ping to ping comparison. It was found that two serious software bugs were likely to have influenced the calibration procedure of the EK80 software. One of these impacted the comparison of HERAS FRV Tridens records and lead to Sv gain offsets of 1.76 dB. After the correction, the measured acoustic intensities were comparable between EK60 and EK80 implying that the interchangeable application of these tools on board SCH6 should not affect species classification and measurements should be similar between vessels either using EK60 or EK80 given the instruments are calibrated correctly. The calculated relative frequency responses from the acoustic recordings of these three fishing vessels showed that FV Willem van der Zwan SCH302 and FV Alida SCH6 were found reasonably coherent, but FV Afrika SCH24 was different. These differences are associated with lower mean backscatter ...