Do Hatchery Salmon Dominate Rivers?

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Recent reports by UC Santa Cruz and others have demonstrated that only ten percent of salmon returning to the Mokelumne River are wild. The balance or majority are hatchery raised. The studies report that many hatchery fish are unmarked and thus require scientific evaluation to determine their origin. Scientists have developed a method to examine the growth pattern of the otolith of fish to determine if they are hatchery or wild raised. Hatchery fish receive more food as fry and thus produce more and smoother growth rings in the otolith. This study of course has implications to all of our California salmonid rivers. See the following link to read the whole story:

Enquiry to the California Department of Fish and Game revealed that the Department of Fish and Game does not own any of the salmon and steelhead hatcheries in the Central Valley. All of them are owned by the entities who built, manage, and profit from the dams that block upstream migration of salmon and steelhead to prime spawning and rearing habitat. This includes U.S. Bureau of Reclamation (Nimbus and Folsom Dams on the American River) with whom Rachel Johnson is affiliated. These entities are required by California Fish and Game Code (legislative act) to build, maintain, and pay the Department to operate these hatcheries as mitigation for hundreds if not thousands of miles of prime salmon and steelhead spawning habitat lost above California's dams. These dams are the true cause of the decline of salmon and steelhead in California. On the Mokelumne the dams and the hatchery are owned by the East Bay Municipal Utilities District who are required by law to pay the Department to operate the facility.

The Department is aware of the state of wild salmon in our Central Valley rivers and is looking at ways to increase the spawning success of wild fish by using gravel augmentation, reducing the amount of straying of returning adults, better survival of juveniles to the ocean being some of the programs we are now implementing and studying.

The Mokelumne River has undergone several of the above mentioned studies to help wild fish survive and keep the populations sound.

The DFG biologist points to limitations in Johnson's study on the Mokelumne River. "Her study has some very specific limitations based on the amount and validity of data collected in 2004. In 2010 we collected over 7,000 CWT and came up with different figures for different parts of the river sampled. Please look at the sample sizes used in Johnson's analyses and the methodology of extrapolation. The UCSC summary does not go to the heart of the issue of data used, annual variations in water flows, portions of river studied work done to restore natural habitat and planting practices."

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