Pacific sardine populations fluctuate with water temperature. Colder water means fewer fish. Temperatures last fell in the 1940s, but heavy fishing continued, devastating the stock and ending fishing until sardines returned when waters warmed in the 1980s.
“We think this is set to happen again,” says Zwolinski, who tracked the population over the past century. He found that sardines have reproduced less since waters cooled in the 1990s.
As far south as California the fishermen are complaining of cold water:
Federal fisheries managers slashed upcoming West Coast sardine harvests by two-thirds while scientists try to get a better handle on indications the population is significantly dwindling… Populations typically drop when ocean temperatures get colder, as they have lately in conjunction with a climatic condition known as the Pacific Decadal Oscillation.
