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This manual was developed with the purpose to improve the quality of maturity data of herring (Clupea harengus L.), and thereby the basis for estimation of spawning stock biomass applied in stock assessment and management as an indicator of stock reproductive potential. The maturity scale presented includes eight maturity stages for each sex. The macroscopic maturity stages are based on a histological evaluation of gonadal development. The manual and analyses were based on samplings of herring obtained from the central and western Baltic.

The macroscopic stages are illustrated in different ways in order to reduce differences in subjective judgement and thereby increase the accuracy of stage identification using the approach of Tomkiewicz et al.(2002). In addition, light microscopy of oocytes is suggested as a means of immediate verification, while histological criteria are included as a means for subsequent validation. The histological classification criteria are included and similarly illustrated.