Science Spotlight

With less competition from non-native species, native Lahontan cutthroat trout are growing larger in Silver Creek.

Amid the intense, physically demanding native trout restoration work taking place in the fall of 2022 on Silver Creek, Mono County, Nick Buckmaster allowed himself a momentary indulgence.

A senior environmental scientist supervisor with the California Department of Fish and Wildlife (CDFW), Buckmaster paused long enough to imagine himself camped on the banks of Silver Creek within the Humboldt-Toiyabe National Forest, perhaps on vacation, maybe in retirement. It was a warm, summer evening in his mind’s eye, and Buckmaster was casting a dry fly to rising wild and native Lahontan cutthroat trout in the 14- to 16-inch size class.

Such a scenario would have been unthinkable just a couple of years ago. Silver Creek has been closed to fishing of any kind for almost 30 years to protect the remnant population of native trout. Overrun with more aggressive, non-native brook trout despite attempt after attempt to remove them, Silver Creek’s Lahontan cutthroat trout (“LCT” in fisheries parlance) have been clinging to a marginal existence within their home waters.

Today, however, Buckmaster’s dream is closer to reality than it has been in a generation. The Lahontan cutthroat trout recovery work taking place in Silver Creek the last few years represents one of the largest and most ambitious wild and native trout restoration efforts in California history. And nowhere else throughout the Great Basin where Lahontan cutthroat trout were once so abundant is this recovery work happening more quickly, more innovatively and more successfully than in little Silver Creek.

And many eyes are on Silver Creek, a tributary of the West Walker River located about 20 miles northwest of Bridgeport in the hills above the Marine Corps’ Mountain Warfare Training Center. The recovery work there, which will resume in the summer of 2023 as snowmelt allows, is taking place at a moment when federal and state wildlife officials are seeking to accelerate Lahontan cutthroat trout recovery throughout the West. The fish have languished as a listed species under the federal Endangered Species Act for more than 50 years.

Buckmaster and his supervisor, Environmental Program Manager Russell Black from CDFW’s Inland Deserts Region, took on the Silver Creek recovery project in 2020 during the height of the COVID-19 pandemic when social distancing and stay-at-home mandates shut down a lot of other field work. New to the project and passionate about wild trout, the two were either unburdened by decades of past failures at Silver Creek or simply naïve to conventional thinking that Silver Creek and its genetically pure strain of Walker River Basin Lahontan cutthroat trout were a lost cause.

The two supervising fisheries biologists were also on something of a roll having led CDFW’s successful, five-year effort to rescue the federally endangered Owens pupfish, a species so rare it was once declared extinct. That undertaking opened up several square miles of additional pupfish habitat after the removal of non-native, predatory species and helped improve genetic diversity, capturing the imagination of The New York Times in the process.

The same dewatering techniques Buckmaster and Black deployed in the lowlands of the Owens Valley to eliminate non-natives and help pupfish are proving equally effective in the mountains of Mono County to help Lahontan cutthroat trout. Applying those techniques to a small stream environment was a first. For CDFW staff new to the project, training was held last spring at nearby Slinkard Creek (YouTube).

By mid-September, Buckmaster was leading a 10-person crew of fellow fisheries biologists and scientific aids over eight consecutive days of intense field work that involved temporarily lowering flows in portions of Silver Creek (sometimes for a mile or so at a time) to remove the brook trout and relocate the Lahontan cutthroat trout to higher, previously treated reaches upstream that are now brook-trout free. It was Buckmaster’s sixth trip and treatment of Silver Creek of the eight he and his CDFW colleagues would conduct in 2022.

Last year was also a milestone in that CDFW was able to treat all 11 miles of Silver Creek and its tributaries targeted for brook trout removal. The work began at the meadowed, headwaters section and extended 9 miles to rocky, pocket water downstream where a steep waterfall prevents brook trout from moving up into Silver Creek’s higher reaches and best trout habitat.

The goal is not suppression but total removal of the non-native trout within those 11 miles of prime habitat.

“If you leave two brook trout in the system and one happens to be male and the other happens to be female, you’ve lost,” Buckmaster said. “The brook trout will repopulate and take over the creek. And in that case, we might have just as well stayed home and watched football.”

Dewatering Silver Creek begins with installing a temporary sandbag dam. Large, flexible poly pipe not much thicker than a heavy-duty trash bag is attached to the dam, rerouting most of the creek flow more than a mile downstream. Below the dam, the creek is subdivided into quarter-mile sections with barriers installed to block fish movement.

With Silver Creek’s flow significantly reduced and the trout concentrated in the remaining water, electrofishing teams move in, stunning the fish with electrical current and netting those that float toward the surface. The Lahontan cutthroat trout, outnumbered by brook trout 10 to one in Silver Creek’s lower reaches where the September work occurred, are collected and separated from the brook trout. They are measured, recorded and moved upstream of the sandbag dam and released into previously treated sections of the creek. The brook trout are set aside in buckets for later stocking into nearby Kirman Lake for recreational fishing.

Following the initial electrofishing, separate CDFW teams move in with portable pumps to dry up any last remaining pools and puddles that may still be harboring fish. The crews continue to electrofish, move rocks, look under tree roots and probe crevices for fish. A third “clean-up crew” follows behind the pump teams to triple-check the work as water slowly begins to return. The process is repeated over multiple days and over multiple trips.

“No matter how many passes you do with the electrofishing equipment, you keep finding fish until you completely dewater the creek,” Buckmaster said.

While painstaking and physically demanding, dewatering has proven more efficient, less costly and more environmentally friendly than alternative recovery measures used in the past.

CDFW treated Silver Creek with Rotenone in 1994, 1995 and 1996 only to see brook trout return in the early 2000s. Over the past 20 years or so, a variety of government agencies, conservation organizations, fly-fishing clubs and other permitted volunteer groups have also contributed to recovery efforts with periodic brook trout removal. And yet the non-natives persisted.

“Dewatering is an amazing tool,” explained CDFW’s Black. “We’re able to both remove the invasive species and at the same time put that native species right back into the system the same day. That’s having a real positive benefit for LCT while not impacting the creek or the invertebrate community.”

Restoring Silver Creek for Lahontan cutthroat trout has positive ramifications for other native species. As the brook trout population is eliminated, CDFW scientists are encountering more Sierra Nevada yellow-legged frogs. As Silver Creek becomes more hospitable to Lahontan cutthroat trout, it paves the way for the potential reintroduction of other native fish such as speckled dace, mountain whitefish and mountain sucker.

“It’s an all-around win for all native species in what’s a climate-resilient habitat,” Buckmaster said.

Among the end goals, said Black, is to reopen Silver Creek once again to recreational fishing, most likely as part of CDFW’s Heritage and Wild Trout Program, giving anglers a chance to catch wild Lahontan cutthroat trout in their native habitat in a spectacular setting. That prospect may still be a few years away. Black estimates Silver Creek will need two or three additional seasons of dewatering treatments to confirm the complete absence of brook trout. Subsequent monitoring could also be accomplished through eDNA, which can detect brook trout presence simply by testing water samples.

Since 2020, about 15,000 brook trout have been removed from the system, and Lahontan cutthroat trout appear to be thriving in Silver Creek’s upper reaches that are now mostly brook-trout free after multiple dewatering treatments.

“We’re seeing young-of-the year LCT in the headwaters, which we’ve never really seen before, and we’re getting large numbers of adult fish in the system in the 1- to 2-year-old age class,” Black said.

Last fall, some of those adult trout measured 12- to 14-inches in length. It’s the stuff of fly-fishing dreams.

CDFW Photos: Wild trout experts Allison Scott and Gabriel Singer probe for brook trout as a portion of Silver Creek is pumped dry. Signage along Silver Creek proclaims Lahontan cutthroat trout a "California Treasure" and directs anglers to nearby waters that are open to fishing for the native species. Large, flexible poly pipe reroutes most of Silver Creek's water flow around the work zone targeted for brook trout removal. Nick Buckmaster surveys the work taking place at Silver Creek in the fall of 2022.

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Media Contact:
Peter Tira, CDFW Communications, (916) 215-3858

In the heart of California’s Sacramento-San Joaquin River Delta lies a 3,000-acre flooded island called Franks Tract.

Before humans diked and drained Franks Tract to grow potatoes, grains, asparagus and corn, the island was part of a vast freshwater marsh. Breaches in levees flooded Franks Tract in 1937, and farmers never reclaimed the island. Franks Tract today is a nexus point of many delta uses, ranging from duck hunting and bass fishing to fresh water supply for California cities and farms.

But the island is also a hot spot for invasive plants and predatory fishes, as well as a conduit for saltwater intrusion into waterways used to convey freshwater supplies to cities and agriculture in the Delta and other parts of California. For these reasons, Franks Tract is considered a strong candidate for partial restoration.

“Franks Tract is a microcosm of many of the larger problems pervading the inner Delta, said Carl Wilcox, Delta policy advisor to the director of the California Department of Fish and Wildlife. “Some native fishes are in serious decline, improving the quality of available habitat in the Delta and increasing resilience to drought and climate change could support their persistence and recovery.”

Various partners, led by CDFW, are proposing to restore about 1,000 acres of Franks Tract to tidal marsh. The proposed restoration is consistent with the Delta Smelt Resiliency Strategy, state goals for the Franks Tract State Recreation Area, and state water quality control plans for the San Francisco Estuary. The effort also aligns with the multi-agency Delta Conservation Framework and the Central Delta Corridor Partnership.

The proposed restoration could shrink waterweeds, grow fish food, create habitat for Delta smelt and other declining species, and prevent salinity intrusion into the south Delta. It may also improve recreational opportunities for residents and visitors.

Results of hydrodynamics modeling indicate the proposed restoration would provide more fresh water to the central Delta shielding regions upstream from ocean saltwater intrusion. A 2017 UC Davis survey documented year-round use of Franks Tract and surrounding channels by locals, visitors and researchers, and seasonal use by hunters, anglers and boaters. Many survey respondents were concerned about changes in access to the water and effects on the local economy and sport fishing, which is dependent on that access. The survey yielded useful information for the next, more detailed, planning and design round including a locally proposed alternative design.

“We will continue to work with stakeholders to not only address habitat and water quality priorities, but also enhance recreational and sport fishing opportunities,” Wilcox said.

A recently released report, Franks Tract Futures: Exploring Options for Multi-Benefit Restoration and Increased Resilience in the Central Delta Corridor, summarizes the technical studies and stakeholder input that’s been collected relative to the potential restoration of Franks Tract.

If approved for further development, the Franks Tract restoration proposal would enter a second phase of planning, design and environmental review with a target end date of December 2020.

CDFW Photos.

California’s drought emergency was officially declared to be over last year, but its deleterious impact on fish habitat is still being felt in many parts of the state -- especially in arid parts of Southern California. In order to help offset these effects at one site in northern San Diego County, CDFW biologists and other staff recently toiled to create spawning beds for rainbow trout.

The Sweetwater River is a second-order stream located within Cuyamaca Rancho State Park. The underlying rock is granite, which, as it erodes, creates sand that accumulates in the low-gradient portion of the river. Previous surveys in the Sweetwater River revealed a lack of high-quality spawning habitat for the rainbow trout population, which was reduced by 70 to 80 percent during the recent drought.

Seeing an opportunity to restore habitat to this waterway, South Coast Region fisheries biologists came up with a plan to place suitable materials into Sweetwater for the rainbow trout to use for new spawning grounds. Beginning on March 20, CDFW Environmental Scientist Russell Barabe, scientific aids Joseph Stanovich and Ken Sankary and volunteer Mark Berlin worked in the hot sun and dry conditions to rehab the streambed. Using a nearby dry stream channel, the team shoveled hundreds of pounds of rocks and materials through mesh screens to remove fine sediment and sand and clean the rock, called cobbles, to make them ready for placement into Sweetwater River. All the rock had to be moved one bucket at a time and poured into pool tailouts (the downstream end of a pool where the water gradually shallows) to create spawning beds about three feet square for rainbow trout.

Though similar work has been done in northern California – specifically two larger-scale projects in the American and Sacramento rivers, which served as the inspiration for this project – it had never been done in this small a stream before.

This small but important project could increase the spawning success of a drought-reduced population in a stream with easy public access. If successful, this project could be used as a model for future habitat restoration activities in other small trout streams. The fisheries team’s work is an example of how our scientists put the mission of CDFW – to conserve California’s fish and wildlife resources for the use and enjoyment of the public – into action.

CDFW Photos. Top Photo: CDFW Scientists hauling buckets of rocks to create spawning beds for rainbow trout.

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A tiny transponder is placed inside the body cavity of each female salmon. When the fish lay their eggs, the transponders will be expelled, providing scientists with information on when, where and how successful each spawning female is.


After the salmon are tagged, they are returned to a holding pond while the anesthetic wears off.


CDFW scientists electronically identify and perform an ultrasound on each fish in order to assess their pre-spawning condition.


Each salmon in the project received a tiny identity tag that is entered into a database. The computerized system allows biologists to follow individual fish throughout their life cycle.


A team of scientists read, evaluate and record data for each individual salmon.

On Thursday, May 18, fisheries biologists implanted acoustic transponders into 60 endangered adult spring-run Chinook salmon. The transponders will track their movements and help determine spawning success later this season. The salmon will be released to spawn naturally in the San Joaquin River near Friant over the next three months.

Spring-run Chinook have been absent from the river for many decades. Reintroduction is one of multiple strategies biologists are using to reestablish naturally spawning runs of these fish as part of the San Joaquin River Restoration Project. The project – which is jointly coordinated by CDFW, the Bureau of Reclamation, the California Department of Water Resources, the U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service – is a comprehensive, long-term effort to restore flows to the San Joaquin River from Friant Dam to the confluence of the Merced River and restore a self-sustaining Chinook fishery while reducing or avoiding adverse water supply impacts from restoration flows.

A total of 120 salmon will be implanted and released at two different times. Biologists will track the fish from each release to determine which is most successful. This release strategy provides the hatchery-raised salmon the opportunity to select their own mates, construct redds (a spawning nest in the stream gravel) and spawn naturally.

CDFW photos by Harry Morse