Mendocino Coho Salmon Conservation Rearing Effort

Background General Info: Central California Coast coho salmon are both a federally and state-protected species. They were listed as threatened under the federal Endangered Species Act in 1996, and subsequently reclassified as an endangered species in 2005. The California Fish and Game Commission designated coho salmon from San Francisco to Monterey as endangered under the California Endangered Species Act in 1995, and subsequently in 2002 designated coho salmon from Punta Gorda to San Francisco as endangered. A State coho salmon Recovery Strategy was adopted by the California Fish and Game Commission in 2004. The Federal Recovery Plan was released in 2012, and in 2015 NOAA Fisheries included coho salmon in their ‘Species in the Spotlight’ initiative to bring greater attention and  resources to save one of the nation’s most highly at-risk species.


Federal and state agencies, along with landowners and non-governmental organizations, are taking extraordinary measures on the south coast of Mendocino County to save a critically endangered species. Members from the U.S. Army Corps of Engineers (USACE), the National Oceanic and Atmospheric Administration (NOAA) Fisheries, California Department of Fish and Wildlife (CDFW), North Coast Regional Water Quality Control Board, The Nature Conservancy, The Conservation Fund, and Mendocino Redwood Company are banding together to conduct conservation rearing efforts for endangered Central California Coast coho salmon.

Coho Salmon

The decision to bring wild coho salmon for conservation rearing was guided by seven years of monitoring in rivers and tributaries of the Mendocino coast.  Despite extensive efforts to restore and improve aquatic habitat for coho salmon, along with some of the best habitat and water quality available in the central California coast, fish populations in Southern Mendocino rivers have not increased.  The numbers of adults returning to breed each year have continued to trend at just a few hundred where they once numbered in the tens of thousands.

This winter, adult coho salmon were returned to the streams where The Conservation Fund, The Nature Conservancy, Mendocino Redwood Company, and agency partners have made big investments in salmon habitat restoration in the last decade.  Fish were released in small groups with genetically suitable partnersin time for them to do what they would naturally do at this time of yearswim upriver and mate. Since the release, scientists have been thrilled to observe the released coho salmon mating with each other and with returning salmon from the ocean.

“The numbers of Garcia and Navarro River adult coho salmon returning to spawn in four of the last ten years have been below the threshold of fish necessary to maintain a viable population,” said CDFW’s Allan Renger, “and this conservation rearing pilot project relies on fish population monitoring to make informed decisions on when, how, and where to act.” 

To keep these salmon populations from becoming locally extinct, actions were taken to capture a small number of juvenile coho salmon from the Garcia and Navarro Rivers. Starting annually in 2018, approximately 200 juvenile coho salmon were removed from the two rivers and carried out of the woods in backpacks full of cold water. They were then transported three hours away to Warm Springs Hatchery in Geyserville, Sonoma County.

Juvenile Coho Salmon

The hatchery is co-operated by the U.S. Army Corps of Engineers and the California Department of Fish and Wildlife. At the hatchery, the salmon were tagged, genotyped, and raised to adulthood.  Funding from The Nature Conservancy, The Conservation Fund, and NOAA Fisheries made this possible.

 “The diversity of partners involved in this effortstate and federal agencies, environmental non-profits, and timberland ownersreflects the seriousness of the situation,” said Jonathan Warmerdam, with the North Coast Regional Water Quality Control Board. “We simply can’t allow these salmon to disappear as they did in the Gualala in 2004. This is really an ‘all-hands-on-deck’ effort to maintain and then recover these salmon.”  Salmon are a keystone species and represent the health of an ecosystem.

Researchers believe one of the reasons salmon populations are not responding to habitat improvements and availability is due to the ecological and genetic effects caused by severely depressed population numbers over the last decade. 

The situation for these fish was exacerbated during California’s severe drought in 2014 and 2015. During these years the river flows in Southern Mendocino County and elsewhere were so low that access for coho salmon to migrate upstream to spawn was extremely limited. This drove their already historically low numbers to even more dangerous levels, hindering successful spawning.

Coho salmon in streams and rivers along California’s central coast have been falling below critical threshold biologists call “population depensation.” This results when there are so few salmon returning to a stream that they are unable to find a mate, causing their numbers to decline until extinction. And if a male and female do cross paths to spawn, they may be closely related, causing inbreeding. Such pairing can result in fewer offspring and genetic defects which can weaken the overall population.

“We know what the approximate depensation number for each watershed is based on its potential habitat size,” said Bob Coey, North Coast Branch Chief with NOAA Fisheries West Coast Region in Santa Rosa. “For example, the threshold in the Garcia River is about 75 returning adults and about 200 in the Navarro. Unfortunately, numbers of returning adult coho salmon have fallen below this threshold in several of the last eight years, perpetuating and accelerating the downward spiraling abundance towards local extinction. It became clear that 2018 was the right time to act.”

Coho Salmon Being Released

NOAA, CDFW, and USACE fisheries scientists reared the captured coho salmon at the hatchery and built what is called a “genetic breeding matrix”, which is a scientific spreadsheet that identifies compatible mating pairs based on each fish’s genetic makeup. The matrix matched those that are the least related to develop options for release that maximize genetic diversity and reduce the chance of mating between close relatives.

This approach will supplement coho salmon populations in the Garcia and Navarro Rivers, minimizing further erosion of genetic variability for the species, and hopefully boost population numbers.

“Since 2005, over one-third of the Garcia watershed has received conservation protection, more than twelve miles of stream habitat have been restored, and the majority of the forests are managed sustainably,” said Jennifer Carah, Senior Scientist with The Nature Conservancy. “We are very hopeful that with a little matchmaking help the fish will bounce back and fully take advantage of these areas to thrive.”

“Hopefully this will be the final step in a years-long process to improve habitat through sediment reduction projects in the Garcia River watershed,” said Scott Kelly, North Coast Timberland Manager with The Conservation Fund.  “This years-long effort has improved the roads and forest infrastructure of our Garcia River Forest, directly enhancing instream habitat by adding large wood for cover and to sort and restore spawning gravels in our streams.” 

This conservation rearing effort closely mirrors the actions taken in 2001 to help revive coho salmon in the Russian River watershed, in Sonoma County, when their numbers had declined to less than a dozen returning adults. A conservation rearing program there used a similar breeding matrix to ensure the greatest genetic variability for their offspring. As a result of this conservation-based breeding program at Warm Springs Hatchery, and continuing efforts to improve fish habitat, during the winter of 2017-2018 the program had its best year of returns to date and upwards of 700 adults returned to spawn.