Southern California’s coastal fish populations plunged in recent decades, according to a new study that analyzed the number of fish trapped each year at five power plants.
The study, published in the journal Estuarine, Coastal and Shelf Science, calculated that overall numbers and biomass of fish — including commercial species and those not commonly caught — declined by 78 percent between 1972 and 2010, the period reviewed in the study.
Authors John McGowan, a professor emeritus at the Scripps Institution of Oceanography in La Jolla, and Eric Miller, a senior scientist with the consulting firm MBC Applied Environmental Sciences in Costa Mesa, examined the fish entrapment rates at five Southern California power plants during that period.
Those facilities, including the San Onofre Nuclear Generating Station, trapped more than 10 million fish About 150 species were affected, making the power plants unexpected laboratories for analyzing fish populations.
“These power plant intakes have proven to be wonderful sampling tools for getting figures on the abundance on these fish,” McGowan said.
The study, published Saturday, examined 21 of the most common fish species in the region. The researchers documented a crash in populations of fish such as queensfish and white croaker, as species common to Southern California shifted north. They also saw a slight corresponding increase in fish normally found father south.
The power plant records allowed the researchers to rule out overfishing as the main cause of the population crash. Since entrapment records measured declines in both commercial and non-commercial species, it suggests that ocean conditions rather than commercial fishing are to blame, researchers said.
Moreover, declines in “near shore” fish occurred as California communities were cleaning up stormwater discharges and restoring coastal habitat, so the collapse of fish populations was probably not due to pollution and habitat loss.
McGowan said the likely factors are shifts in ocean ocean condition, that have altered temperature, salinity and plankton abundance.
“We’re not sure why those things have happened,” McGowan said. “There’s no question that the represents a clear-cut, unambiguous change in the physics of the California Current. The physics affect the biology profoundly.”