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Corps Working to Preserve Endangered Salmon

Published Sept. 27, 2019

An extensive effort is underway across coastal regions of Northern California to save the state's endangered coho salmon, a species that has come close to extinction experts say, because of a range of issues including development, overfishing, logging and prolonged drought, circumstances that are challenging environmentalists determined to restore the most vulnerable and sensitive of the salmon species. 

In Sonoma County in 2001, less than a dozen adult coho salmon returned from the ocean to spawn in local waterways.  And despite extensive efforts to restore and improve aquatic habitat for coho in neighboring Mendocino County, those numbers have not increased significantly either.  "There are just not enough adults returning and spawning successfully," said Ben White, a fisheries biologist at the U.S. Army Corps of Engineers' Don Clausen Fish Hatchery in the Sonoma town of Geyserville.  The hatchery is now partnered with a variety of government agencies and conservation groups on a project designed to increase the number of coho salmon in Northern California waterways.  "I think these fish are getting hit extra hard because of things like drought, all the water diversions going on, all the stress on our landscapes from development and urbanization," coupled with the coho's short and rigid lifespan, said White.

After having success raising wild coho from the Russian River watershed, the Corps is now tapping two decades-worth of salmon rearing experience to revive coho in next door Mendocino County.  Recently, White and others waded into the Garcia and Navarro Rivers to collect more than 200 juvenile coho which will be raised to adulthood in sprawling tanks at the Don Clausen hatchery before being released back into local waterways to spawn naturally on their own.  The effort to restore endangered coho is compounded by the fact that the species by nature has a very high mortality rate.  "If we pull in 250 fish from the wild as juveniles, you would only expect two or three of those to make it back from the ocean as an adult based on their survival in the wild," said White, "whereas, if you bring them to our facility, I have an 85-90 percent survival rate to adulthood, so I can return over 200 fish to the wild to spawn naturally." 

Research conducted by the National Marine Fisheries Service had shown that when coho salmon populations are severely depleted, inbreeding results, further affecting the livelihood of the species.  To prevent that, DNA testing will be conducted while the fish are in captivity to identify compatible mates based on their relatedness to one another.  When ready, the coho will be released back into the Garcia River watershed with suitable spawning partners to breed naturally in the wild, while at the same time improving genetic diversity among the population.

Given that the Corps' fish hatchery in Geyserville has been able to help restore endangered coho populations there, White is optimistic about improving Mendocino's stock.  "I think we can make a difference.  I feel like we have a community that's really involved.  You don't want to wait until the fish are gone."

The project is a partnership with NOAA, the state of California and several conservation groups including the Nature Conservancy, the Conservation Fund as well as private landowners.