by Rachel Nuwer, NYTIMES.COM
Since 1964, the Mokelumne River Fish Hatchery in California has supplied the watershed with four to 10 million juvenile Chinook salmon each year. The hatchery began the practice as a way of countering the effects of dams that block migration and making sure that the salmon population remained viable. But recent research shows that the massive influx of hatchery-raised fish is masking the fact that wild fish populations are not holding up.
“Without distinguishing hatchery from wild fish, the perception is that we have healthy salmon surviving in a healthy river,” said Rachel Johnson, a fish ecologist affiliated with the University of California, Santa Cruz, and the lead author of a new paper published in the journal PLoS One.