The herring resource was previously divided into the Georges Bank and Gulf of Maine stocks, based not on genetic but morphometric differences (Overholtz, 2006) and the Georges Bank/Nantucket Shoals and coastal Gulf of Maine herring have been identified as two distinct spawning components with many smaller units embeeded within those (Vonderweidt et al., 2008). However during most of the year herring are mixed and are caught together in the fisheries and in research surveys so the components are combined for assessment and management purposes into a single coastal stock complex.
Image: "Whitehead, 1985 FAO Species Catalogue. Vol. 7. Clupeoid fishes of the world (suborder Clupeoidei). An annotated and illustrated catalogue of the herrings, sardines, pilchards, sprats, shads, anchovies and wolf-herrings" via FishBase