Study finds steep drop in key coastal fish

Study finds steep drop in key coastal fish
Sardines are one of the schooling fish that plummeted in population, according to a long-term analysis of records of fish caught in power plants. With fewer schooling fish, larger fish and sea lions have been negatively impacted. Photo courtesy of Scripps Institution of Oceanography

COAST CITIES — Populations of fish in Southern California declined more than 78 percent on average over the past 40 years, according to a recent study. 

The authors arrived at that conclusion after examining a rather unique source: records of fish captured in cooling systems at five coastal power plants, including the San Onofre Nuclear Generation System.

Since 1972, the power plants trapped more than 10 million fish as they filtered in seawater for their cooling systems. Under state law, the facilities are required to document the fish and issue regular reports.

“I was attracted to this study due to the sample size — millions of gallons of cubic yards of water going into the plants a few times every year,” said co-author John McGowan, a professor emeritus at the Scripps Institution of Oceanography.

The study, published last month, looked at 21 common fish species in Southern California during the past four decades. From queensfish to anchovies, the populations for nearly all types of fish declined sharply.

“I would be skeptical if data was only collected at one power plant, but the results from the five plants were similar,” McGowan said. He noted that it’s “extremely unlikely” the fish learned not to swim near the power plants since they have limited cognitive abilities.

The power plant records are largely consistent with other independent fishing stock assessments. Those assessments also show an ongoing decline in many of the same fisheries over the past 30 years, according to McGowan.

The findings indicate the fishing industry isn’t the main cause of the big drop in counts. That’s because both commercial and non-commercial species suffered similar population declines.

Of all the species, schooling fish like sardines were hit hardest. And consequently, seabirds, sea lions and larger fish had less food to prey on, hurting their populations, according to the research.

“The entire ecosystem is thrown off,” McGowan said, adding that not only has there been a drop in schooling fish numbers, but those fish weigh less on average.

The study notes that ocean temperature changes, spurred by global warming, likely explain the drop-off. And the shift in ocean salinity is another likely factor.

“More studies should look at the effects of global farming,” McGowan said.

McGowan said the power plant records are a valuable resource scientists can “continue to utilize into the future.”

The study, “Faunal shift in Southern California’s coastal fisheries: a new assemblage and trophic structure takes hold,” was published in the July 20 issue of the “Journal of Estuarine, Coastal and Shelf Science.”



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