Atlantic herring (Clupea harengus) is widely distributed in the Northwest and Northeast Atlantic. Within the Northeast Atlantic, they are distributed from the northern Bay of Biscay to Greenland, and east into the Barents Sea.

Stock distribution is uncertain for Atlantic herring in this area.  Many local populations with differing growth rates share similar habitats and may mix during certain times of the year.   There is some evidence that western Baltic spring-spawning herring (Division 3a and subdivisions 22–24) and central Baltic herring (subdivisions 25–29 and 32, excluding Gulf of Riga herring) are mixing in subdivisions 24 (ICES 2017). Also, a large portion of the herring in this area are North Sea autumn spawners(NSAS)(ICES 2017) which are considered elsewhere.

A mixed-stock analysis was developed for populations spawning in the area spanning the North Sea to the Baltic Sea including the main stocks WBSS and NSAS plus others. The study indicated that contributions from WBSS to the management unit could have been largely overestimated. They also show that the population of WBAS ascribed as low fisheries importance contributes non-negligible and potentially temporally increases proportions to mixed-stock aggregations, calling for a reevaluation of stock definitions (Bekkevold et al. 2023).

This report covers western Baltic spring spawning herring (WBSS) in subdivisions 20–24.