A decades-long collaboration is giving Central California’s dwindling coho salmon population a fighting chance.
By Annie Roth, UC Santa Cruz
Nearly every day for the past 20 years, scientists from UC Santa Cruz and the National Oceanic and Atmospheric Administration (NOAA) have waded into Scott Creek, a 12-mile-long burbling stream in Santa Cruz County just a few miles north of Davenport.
Dressed in waders and toting bags and buckets, these scientists navigate the stream’s chilly waters and muddy banks in search of coho salmon. Along the coast of central California, coho salmon are endangered. But the young salmon in Scott Creek may hold the key to the species’ recovery.
As the southernmost population of coho in the state, the salmon in Scott Creek are adapted to warmer and drier conditions than their more northern cousins. By studying the evolution, ecology, and genetics of this population, scientists at UCSC and NOAA hope to gain insights that could help them ensure the survival of the species throughout California.
The project at Scott Creek is one of many that UCSC and NOAA have undertaken together to prevent the extinction of California’s iconic salmon. Since joining forces 25 years ago, the federal agency and the university have become the largest and most strategic force fighting to conserve salmon in California. But with climate change, habitat loss, overfishing, invasive species, and poor water management posing an ever-greater threat to salmon survival, the salmon-saving team continues to have its work cut out for it.
An upstream battle
Coho salmon, also known as silver salmon, are one of seven Pacific salmon species. Found from Alaska to Central California, these fish are anadromous, meaning they spend time in both fresh and saltwater.
After spending their first year in freshwater, the fish head out to sea for two years. When they are ready to spawn, they return from the ocean and swim up rivers to the freshwater habitats where they were born. After spawning, the fish die, leaving their remains — full of essential nutrients from the ocean — to be transferred to the land.
Coho have been a part of the diet and traditions of California’s Indigenous peoples since time immemorial. The Karuk, for example, are also known as the “salmon people,” due to the large role salmon play in their culture. Before European colonization, hundreds of thousands of coho spawned in rivers and streams across California. By the early 2000s, however, their numbers had fallen to less than 5 percent of their historic levels.
California’s coho are experiencing “death by a thousand cuts,” said Cyril Michel, a project scientist who works with UCSC’s Fisheries Collaborative Program. “There’s no one smoking gun.”
All salmon species in California face myriad threats to their survival. In the 19th and early 20th centuries, coho and other salmon species were fished to the brink of extinction in California. Central California Coast (CCC) coho were hit the hardest, prompting lawmakers to list them as threatened under the Endangered Species Act in 1996.
Although the move resulted in reduced fishing pressure, the population kept shrinking. Coastal development, the construction of dams, the eradication of beavers (the ponds they create are ideal habitat for young salmon), and water diversions for agriculture had reduced the amount of habitat available to the fish. And to make matters worse, a combination of pollution, invasive species, and climate change was degrading the little habitat remaining.
In an effort to boost the coho population, UCSC and NOAA teamed up with the Monterey Bay Salmon and Trout Project and began rearing fish in conservation hatcheries and releasing them into the wild. They began releasing coho into Scott Creek in 2001, but eventually expanded to Pescadero Creek and several other locations in the Santa Cruz Mountains.
Though the hatchery’s efforts helped give local coho numbers a boost, it did little to address the sources of their decline. “Hatcheries can help in the short-term,” said Eric Palkovacs, professor of ecology and evolutionary biology and director of the Fisheries Collaborative Program at UCSC, “but ultimately recovery is going to depend on the restoration of wild intact ecosystems.”
Around this time, NOAA opened the Santa Cruz Laboratory to house the Southwest Fisheries Science Center’s Fisheries Ecology Division, where scientists from the agency could collaborate with scientists from UCSC on a wide range of projects, including conserving CCC coho.
One of the first places scientists from NOAA and UCSC started studying coho was Scott Creek, and their initial discoveries were shocking.
“There was a stretch from 2009 to 2011, where the number of returning coho salmon each year was less than five individuals. They were almost gone,” said Joe Kiernan, a research ecologist at NOAA’s Southwest Fisheries Science Center.
At the time, bringing coho back to Central California seemed like a daunting task. After all, how can you conserve coho in a place where droughts are frequent and dams and water diversions are pervasive?
Unperturbed, the scientists started wading out into Scott Creek each day in search of answers. “There are no coho south of Santa Cruz; we’re at the southern end of their range,” Michel said. “We’re probably going to see the impacts of climate change earlier and in more extreme ways than some of the more northern populations, so the front line of keeping these populations alive is going to be here.”
Over the past twenty years, dozens of researchers from NOAA and UCSC marched to the front line to fight for the CCC coho. They started reintroducing coho to places they had disappeared from and studying their survival; identifying which habitats were capable of supporting coho and which habitats needed restoration in order to do so;
tagging coho to map their movement patterns; creating more accurate methods for measuring how many coho remain; building a genetic library of wild coho; and conducting climate tolerance experiments on captive ones. Many of these projects are still underway today, and more are on the horizon.
“We’re trying to produce research that’s actionable,” said Michel. “Research that shows regulators things we can do differently to benefit salmon populations.”
Using what they’ve learned from their various research projects, NOAA has been able to develop and implement action plans to conserve CCC coho and other at-risk salmon. Over the past decade, these action plans have resulted in half a dozen dam removals, the restoration of vast stretches of salmon habitat, and more targeted hatchery releases. Nonetheless, the agency’s latest 5-year review of the species’ status, published in 2023, found that many of the threats to the population remain or have increased.
Although CCC coho are far from losing their endangered species status, the work NOAA and UCSC are doing seems to be having an impact. Since their CCC coho collaboration began, the number of salmon in the region has increased. In 2021, researchers counted 420 individual coho spawning in Scott Creek. And in 2024, the number of coho spawning in Mendocino Coast rivers reached its highest level since monitoring began 16 years ago, with a whopping 15,000 fish.
There are also spawning coho in Pescadero Creek, Waddell Creek, and San Vicente Creek, “which was not the case 15 years ago,” said Kiernan. “It’s a work in progress, but tangible progress has been made.”
“We’ve learned over the years,” said Steve Lindley, the former Fisheries Ecology Division Director at NOAA’s Southwest Fisheries Science Center. “By better understanding what exactly goes right or wrong for salmon, which you can only do by studying them for long periods of time, we’ve gained a lot of insights into what kinds of habitats are important for these fish and what kinds of actions are helpful to improve their status.”
An invaluable partnership
The type of information NOAA and UCSC are working together to gather would be nearly impossible for either group to obtain on their own, said Lindley.
According to Lindley, NOAA brings boats, funding, and scientists with decades of experience in fishery science to the table, while UCSC brings scientists with a wide range of expertise and a never-ending supply of eager graduate students who work hard and provide fresh perspectives.
“We’ve created a center of excellence and expertise around many disciplines that are relevant to sustainable fisheries and conservation of endangered species,” Lindley said. In addition to fishery scientists and ichthyologists, NOAA and UCSC have economists, data scientists, and statisticians in their ranks, ready and willing to lend their unique expertise to the cause of conserving salmon and other species.
Last year, NOAA awarded UCSC a nearly $7.5 million to advance its collaborative efforts to conserve coho and other imperiled Pacific salmon. Having this funding, the researchers say, will allow them to do the kind of research that will make a difference.
“We are getting ever more optimistic about the possibilities for recovering salmon to more healthy and sustainable and harvestable levels,” Lindley said. “There is enormous potential to improve the status of salmon in California while still allowing for humans to do the things that they need to do. Through more careful operation of water projects and ongoing efforts to restore functional habitats for salmon.”
But the chance of achieving this would be zero, Lindley said, “without the kind of scientific partnership that NOAA has with the University of California, Santa Cruz.”
Unfortunately, such partnerships are under threat.
“NOAA is losing employees and funding that may have severe consequences for our ability to continue doing this critical conservation work,” said Palkovacs. “It is not a stretch to say that the future of coho salmon in California depends on how this plays out.”
Despite the cuts, those who remain at NOAA remain determined to see the recovery of Central California’s coho through to the end. And their partners at UCSC aren’t backing down either.
“Opportunities to collaborate across academia and the federal government, between groups with different expertise, is how we can really move the science forward,” said Lindley.
