Herring season starts early in June every year with the traditional auction of the first tub of Nieuwe Haring. After that the herring sold everywhere and herring feasts are organised in many places. One of these is the famous Vlaggetjesdag or ‘flag day’ in Scheveningen. The start date of herring season is usually announced around the end of November.

: https://www.holland.com/global/tourism/information/traditional-dutch-food/taste-the-season-hollandse-nieuwe-herring.htm