Fish Bulletin No. 42. Maturity of the California sardine (Sardina caerulea), determined by ova diameter measurements
Because the California sardine is seldom taken in a ripe condition, a study of the maturity of this fish has proved a very complicated problem. Since 1919 the California State Fisheries Laboratory has conducted an intensive investigation of the sardine but in the 12 seasons covered by the study only 39 ripe or nearly ripe females have been observed. As the gross observations of the state of maturity of the gonads of the sardine have not proved satisfactory, this detailed study of the diameters of the eggs in the ovaries was made. The study has established the dates of the spawning season, the size at first maturity, and the amount of spawning in each locality. Also, the maturity studies have thrown further light on the movements of sardines. The concentration of spawning in the south and a difference between the north and the south in the rate of development of the eggs, indicate that during the winter months sardines are moving southward along the California coast.