Abstract: Reliable TS(L) relationship is required to improve acoustic algorithms of abundance estimation of Baltic herring. The relationships, empirically obtained in different parts of the Baltic Sea, produce up to 8 dB - difference in the herring TS. In order to develop an accurate TS(L) relationship, it is important to analyze factors controlling the TS variability. The possible impact of the regional difference in the swimbladder morphometry, critical in the backscattering by fish, should be considered. The paper is addressed to the numerical analysis of the backscattering properties of the southern Baltic herring. The input morphometric data for the modelling were obtained basing on the X-ray image collection of the herring individuals caught in the Polish coastal zone (ICES Subdivision 26) in November 2011. The optimal methodology of the morphometry study, including the fish catch, transport, storage and the X-ray analysis has been developed. The backscattering sensitivity to the fish morphometry and the width of fish orientation distribution was shown.