Age at first maturity increases with increasing latitude and also decreases with increasing exploitation. Pacific herring can live for 15-16 yrs but few live beyond 9. Aging is routinely done from scales and occasionally from otoliths. The average herring is about 7.5 mm at hatching. Larvae become juveniles about 10 week after hatching at lengths of 25-40 mm.
Growth rates are slower in southern latitudes and maximum size is larger in northern latitudes.
Maximum size is 18 inches and maximum weight is 550 gm. Population Many differences have been found between herring populations at different latitudes such as timing of spawning, age at maturity, and size. Identification of individual stocks has not been clearly defined. There may be numerous stocks in the eastern Pacific range with one in Oregon. In California, each spawning area is managed as a separate stock.