The large numbers of fish in the schools and their rapid coordinated movements serve as an adaptation against predators. They are migratory and may travel distances of more than 1000 km between feeding and spawning habitats over the course of a year. Sardines feed on zooplankton and phytoplankton by filter feeding and selective capture of larger prey. Life span under natural conditions is normally 12 to 13 years, but some are thought to live up to 20 to 25 years. Spawning may occur in the first year.
Eggs are pelagic.
This species was fished to the point of commercial extinction off California under high demand for fish meal and oil and for canned products for direct human consumption. The development of the sardine fishery followed a now familiar pattern of rapid growth and then accelerating decline seen in virtually all fisheries based on small pelagic fish around the world. This pattern is exemplified in the collapse of the massive anchovy fishery off Peru. The Pacific population of Sardinops sagax caerulea collapsed in the early 1960s under heavy exploitation off California, combined with loss of habitat brought on by climate change with cooler waters in the eastern North Pacific. A major fishery based on Sardinops s. was developed in the Gulf of California during the 1970s and has persisted to the present, although drastically reduced catches during several years in the 1990s have raised concern among Mexican fisheries scientists.