Hatchery raised salmon are overwhelming populations of wild-raised Salmon in some of California’s rivers, masking the fact that too few wild fish are returning to sustain a natural population in the river.

“We expected to find hatchery fish, but the sheer number of hatchery fish returning to spawn in the wild is surprising,” said Rachel Johnson, a fishery biologist affiliated with the Institute and Marine Sciences at UC Santa Cruzand with the Bay-Delta Office of the U.S. Bureau of Reclamation. “It looked like a healthy population of fish returning to spawn, but the reality is that without the hatchery fish the wild stocks are not sustaining themselves.”

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