The spatial and temporal distribution of spawning is influenced by temperature. During warm water conditions, the center of spawning has shifted northward and continued longer. Some spawning may occur year-round, but it peaks in April to May and usually occurs at night. Sardines will spawn several times over a season with a large female producing up to 200,000 eggs in a season. Eggs are found near the surface and will hatch in about three days.
Young fish move inshore and congregate into schools near the beach.
They can reach 16 in-ches, but are usually less than 12 in. There is a good deal of regional variation in growth rates, with average size increasing from south to north. In the Pacific northwest, sardine will reach 215 mm after four year and 235 mm after five years. Females will grow faster than males. Some individuals mature in their first year, most in their second.