Commercial fishing can cause fish population imbalance

Writing in Nature, scientists from several institutions and agencies argue that fishing can amplify the highs and lows of natural population variability.

"We found that the variability of the targeted populations was much higher, meaning that fishing tends to amplify both the peaks and the valleys of population numbers," said George Sugihara, a co-author of the paper and an oceanographer at the Scripps Institution of Oceanography at the University of California at San Diego. "Fishing can potentially not only lead to declining stock levels, but cause populations to fluctuate more through time, which could put them at greater risk of collapse than previously thought."

The researchers believe that fished populations become more variable due to the removal of larger, older individuals most capable of reproduction, leaving the population vulnerable to natural stresses like El Niño.

"A ton of fish of the very largest sizes has far more value to future populations if preserved than a ton of smaller fish, which contribute far less to reproduction," said Philip Taylor, director of the National Science Foundation's Biological Oceanography Program, which provided funding for the research.

Sugihara said the study suggests that fish populations need to be managed not only to maintain the total number of individuals but also to target a certain fish population age structure in the stock. He further warned that such fluctuations could serve as an early warning sign preceding a population crash.

The paper appeared as two studies -- one Tuesday from the National Academy of Sciences and another today in the Journal of the American Medical Association -- said that the benefits of eating fish twice a week outweigh the risks presented by methyl mercury and other contaminants.

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