The rise and fall of Pacific sardine, northern anchovy, and Pacific hake off California have been so common that the species were in collapsed condition 29 to 40 percent of the time over the 500-year period from CE 1000 to 1500, according to a new study in Geophysical Research Letters.

Using a long time series of fish scales deposited in low-oxygen, offshore sedimentary environments off Southern California, researchers described such collapses as “an intrinsic property of some forage fish populations that should be expected, just as droughts are expected in an arid climate.”

Even though they are expected, the findings still have implications for the ecosystem, and for fishermen and fishery managers, who have witnessed several booms, followed by crashes every one to two decades on average and lasting a decade or more.

Collapses in forage fish—small fish that are preyed on by larger predators for food—can reverberate through the marine food web, causing prey limitation among predators such as sea lions and sea birds.