Variability of biotic and abiotic factorsin clupeoids life cycle in the Baltic

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Since 1981, acoustic information, collected in a form of calibrated measurements of integrated echoes energy is applied in Sea Fishery Institute to observe the relationships among clupeoids distribution in the Baltic and associated environmental factors. Data were collected during different seasons for each elementary distance units (EDSU) in standardized depth intervals and compared to the values of selected environmental parameters, measured parallel. Acoustic, biological and hydrological data were correlated in space and transferred to the complex data base, enabling 4D analysis of numerous factors, enable to characterize wide range of fish behaviour. The paper presents selected characteristics, describing the variability of environmental factors, within clupeoids short- and long-term life cycle. The analysis of abiotic factors is enhanced by presentation of specially prepared cross-sections of the herring in different stages of the gonad maturity. All the aspects were described with the task to take them into account in the procedures of measuring and modelling the target strength of herring and sprat, particularly in the specific Baltic circumstances