The collapse of California's sardine fisheries between the 1930s and the 1950s had more to do with long-term climate cycles than with overfishing, according to a study by researchers from Monterey Bay Aquarium Research Center.
Fluctuations in water temperature similar to those associated with El Nino, but occurring over a much longer time scale, dramatically affect the life cycles of sardines and anchovies, leading to alternating cycles of surplus and scarcity, oceanographer Francisco Chavez and his colleagues reported in Friday's issue of Science.
By studying records of ocean temperatures, currents, circulation and other factors, the researchers concluded that, for about 25 years, ocean waters across the entire Pacific tend to be slightly warmer than usual, causing sardines to thrive. Temperatures then dip below average for another quarter-century, favoring anchovies over sardines.
They identified cool, anchovy-rich periods from about 1900 to 1925 and from 1950 to 1975. Warmth-seeking sardines ruled from 1925 to 1950 and from 1975 to the mid-1990s.
"We know that these cycles are related to changes in ocean circulation and atmospheric" effects on the ocean, Chavez said.
Because this cycle is much longer than the El Nino periods, the Chavez team is proposing the names El Viejo -- Spanish for "old man" -- for the sardine regime and La Vieja -- "old woman" -- for its counterpart.