The work presented in this paper is carried out under the HydroPêche project with the aim to develop a tool for an automatic optimisation of trawl in order to minimize the drag of the gear. One of the aspects of this project is the experimental investigation of the turbulent flow around bottom trawls. For that purpose, Particle Image Velocimetry measurements in a flume tank are implemented to access to the two-dimensional velocity field around a bottom trawl. Having an important experimental database allows not only the calibration of numerical models aiming at simulating the flow around a fishing net but also the validation of numerical simulation results. Such experimental technique has the advantage in accessing the turbulent flow field and then allows the determination of the main turbulent flow characteristics. Then Proper Orthogonal Decomposition analysis was applied to extract the main coherent structures of the overall physical phenomenon from the measured database. Finally, a spectral analysis of the longitudinal velocity is applied to determine the frequency of the vortex shedding. This analysis show that the Strouhal number is between 0.19-0.3 in this case.