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

CDFW Environmental Scientist Emily Fisher checks DNA tagged fall-run Chinook salmon fry prior to their release into the American River in February 2023.

Under cover of darkness and with a series of cold, late-winter storms building, California Department of Fish and Wildlife (CDFW) staff gingerly released approximately 1.1 million fall-run Chinook salmon fry (Oncorhynchus tshawytscha) into the American River at the Nimbus Fish Hatchery in Sacramento County.

It was an evening of firsts for CDFW on Feb. 23, 2023. It was the first release of fall-run Chinook salmon into the American River in more than three years. Since the spring of 2020, drought conditions have forced the trucking of Nimbus Fish Hatchery juvenile salmon to points within the San Francisco and San Pablo bays.

It was also the first time in decades CDFW has released fall-run Chinook salmon at such a small size. The salmon fry, just three months old and only 1.5- to 2-inches in length, had just absorbed their yolk sacks and had not yet been fed by the hatchery. Typically, fall-run Chinook salmon released from the hatchery are about 6 months old and 3.5- to 4-inches in length.

“By putting these fish out into the river now, they are going to experience the natural environment of the lower American River as natural-origin fish would,” said Jay Rowan, who oversees CDFW’s Fisheries Branch.

Most importantly, the 1.1 million fry released into the Nimbus Basin represent CDFW’s first experiment with DNA tagging fall-run Chinook salmon, what’s formally known in fisheries circles as “parentage-based tagging” or “PBT.” The emerging practice is also being tested at the Coleman National Fish Hatchery near Redding and has been widely used in the Pacific Northwest – but has never been attempted before by CDFW-operated hatcheries.

Not only are the experimental salmon fry half the age and half the size of typical, hatchery-released salmon smolts, they lack the adipose fin clips to visually identify them as hatchery-origin fish and are also without coded-wire tags that can later provide scientists with information about their life history. Instead, these salmon fry are genetically linked to the parents that produced them in a far-less invasive process requiring less human handling.

Three months earlier, on Nov. 29, 2022, CDFW collected and catalogued genetic material (a tissue clip from the caudal or tail fin) from the 500 adult salmon spawned that day at the Nimbus Fish Hatchery used to produce the 1.1 million salmon fry. By collecting future tissue samples from the released fish, CDFW’s fisheries geneticists can link every individual back to the Nimbus Fish Hatchery and the exact pair of parents that produced it.

That data could start arriving as early as this spring when CDFW and coordinating organizations will begin their downstream monitoring of juvenile salmon in the lower American River, taking tissue samples from young fish collected.

 “We will be able to see whether these fish are showing up in the monitoring surveys and following the same migratory cues and timing that we would expect from natural-origin fish,” said Jason Julienne, the senior environmental scientist who oversees CDFW’s Sacramento Valley anadromous fish hatcheries. “And then, over the next two to four years, we will collect genetic samples from unmarked Chinook salmon to estimate how many of these fish returned as adults to spawn.”

About a quarter of the fall-run Chinook salmon produced at Nimbus and CDFW’s other Central Valley anadromous fish hatcheries receive coded-wire tags and adipose fin clips. With parentage-based tagging, however, every individual fish is a potential data source.

CDFW’s research will help inform future fisheries management decisions, including the use of parentage-based tagging in coordination with current marking and tagging efforts, and could provide insight into how various release strategies contribute to survival, straying and adult returns.

“It’s going to take effort on the back end,” Julienne, said, “but we’re evaluating our long-term ability to implement PBT on a larger scale and its potential to be included as a release strategy representative of natural-born juvenile migration timing and whether it allows us to take advantage of more favorable river conditions earlier in the year.”

The 1.1 million experimental salmon fry are among 5.5 million fall-run Chinook salmon that will be raised and released by the Nimbus Fish Hatchery in 2023. That’s a recent production record, according to Nimbus Fish Hatchery Manager Gary Novak. Under normal years, the Nimbus Fish Hatchery produces 4 million fall-run Chinook salmon smolts for the U.S. Bureau of Reclamation as mitigation for the loss of spawning and rearing habitat associated with the construction of the Nimbus Dam. This year, production targets have been increased to help address issues related to drought and a thiamine deficiency impacting Sacramento Valley salmon populations. Even with near-ideal weather and river conditions accompanying the experimental salmon fry release, both Julienne and Novak acknowledged the long odds facing the fish on their journey to the Pacific Ocean.

Said Novak: “By conducting this release at night, we’re hoping to reduce predation from birds and, hopefully, give these fry a head start in finding good rearing habitat in the river.”

CDFW photos

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

The California Department of Fish and Wildlife’s (CDFW) Human-Wildlife Conflicts Program has been recognized for its innovative approach to promoting effective, integrated non-lethal human-wildlife conflict mitigation techniques in California.

The program was one of six recipients of this year’s Integrated Pest Management (IPM) Achievement Awards by the California Department of Pesticide Regulation (DPR) at the California Environmental Protection Agency.

Winners were selected for developing and adopting innovative IPM tools and practices and for helping increase awareness of IPM to inspire future generations of practitioners.

“We live in increasingly close contact with animals (and) continue to see increases in human-wildlife interactions,” said CDFW Statewide Conflict Programs Coordinator Vicky Monroe, who accepted the award on the program’s behalf at a virtual ceremony held on Feb. 23.

“With this program, we work to communicate that we don’t exist in isolation from other species,” Monroe said. “We are in fact a part of nature. We interact in that shared environment, and share space and resources, with those co-existing species. We offer up a clear vision for human-wildlife interactions and how to mitigate those from escalating into conflict, and how we can promote a safe co-existence with wildlife species. It's really meaningful work.”

“We’re humbled for this recognition, and we’re overwhelmed with gratitude to have been selected to receive this award – particularly for promoting integrated non-chemical and non-lethal human-wildlife management techniques,” she said.

The full 2022 IPM Achievement Awards ceremony (Video) and a shorter video highlighting the Human-Wildlife Conflicts Program’s work (Video) can be found on DPR’s YouTube page. Assemblyman Josh Hoover (R-Folsom), Los Angeles County Deputy Agricultural Commissioner Jim Hartman, and Cougar Conservancy Director Korinna Domingo all made videos congratulating the statewide team on winning the award.

CDFW is the lead state agency responsible for responding to human-wildlife conflict and depredation (wildlife damage to property) in California. The Human-Wildlife Conflicts Program, established in 2018 and expanded in 2022, works to increase CDFW’s ability to be responsive to local communities and to provide public education about wildlife conservation.

The Human-Wildlife Conflicts Program supports Wildlife Watch, created a Human-Wildlife Conflict “Toolkit,” and launched a Wildlife Damage Management speaker series. The program’s leadership helped recruit a statewide team of Regional Wildlife Conflict Specialists and have trained them with the skills and equipment needed to serve local communities, agency partners and the diverse constituent interests statewide. In April 2022, the program graduated the first ever training cohort from its Wildlife Conflict Training Academy.

CDFW would also like to congratulate co-winners of the 2022 IPM Achievement Awards: Cal Poly Strawberry Center, Oracle Park, Vineyard Team, the Appropriate Technology Transfer for Rural Areas Program, Western Regional Office of the National Center for Appropriate Technology, and Lifetime Achievement Award Winner Chris Geiger.

DPR Director Julie Henderson said, “Integrated Pest Management is an essential practice for protecting people and the environment and is a foundational element for the state’s approach to accelerating a systemwide transition to safer, more sustainable pest management.”

For more information see DPR’s news release on the Integrated Pest Management Achievement Awards.

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Media contact:
Ken Paglia, CDFW Communications

Thanks to funding approved in the state budget, the California Department of Fish and Wildlife (CDFW) is now in the process of building upon its existing beaver management policies and laying the groundwork for projects that harness beavers’ natural ability to improve California’s ecosystems.

The state budget approved $1.67 million in fiscal year 2022-23 and $1.44 million in fiscal year 2023-24 and ongoing for CDFW’s beaver restoration program.

CDFW is currently hiring five dedicated scientists to work on a comprehensive approach to beaver management. Once hired, staff will work on numerous projects and collaborations including developing a toolkit to help prevent property damage due to beaver activity and to foster co-existence with the keystone species. Staff will also collaborate with partners on ongoing and future restoration projects to relocate beavers into watersheds where their dams can help restore hydrologic connectivity and promote resiliency to climate change and wildfire.

“We’re incredibly excited about the direction the department is going with its beaver restoration program,” said CDFW Deputy Director Chad Dibble.

Anyone paying attention to wildlife in the media recently may be seeing that beavers are having a moment. A recent article in Mother Jones posed the question: “Is it possible that beavers got a publicist?” The article concludes that beavers are finally getting the “rebrand” they deserve. While beavers have always been known for building dams and altering waterways, perhaps less publicly known is the positive impact they have on larger ecosystems surrounding their dams.

“Beaver dams raise groundwater levels and slow down water flow which allows water to seep into the soil and helps create riparian wetlands that support plant, wildlife and habitat growth,” said CDFW Director Chuck Bonham in an Op-ed written for CDFW and published in Outdoor California magazine.

By aiding healthy riparian growth, beaver dams can mitigate drought impacts and support climate change resiliency. The process of increasing fuel moisture and helping larger areas of land retain water can potentially stop or slow the spread of wildfire moving through an area. Beaver dams also improve water quality and help rejuvenate habitat for salmon and aquatic insects.

At one point, there were between 100-200 million North American Beavers in North America. However, due to unregulated trapping and habitat loss, by the late 1800s they were eliminated from much of their natural range. The current beaver population in North America is estimated at about 10-15 million.

Over the past several years, CDFW has spent millions of dollars partnering with tribes, NGOs, landowners, and state and federal agencies implementing beaver restoration projects. With its new beaver restoration program, the department is embracing the paradigm shift surrounding beavers and continuing its work to bring together collective knowledge and implement a comprehensive approach to beaver management.

“We’re continuing collaboration with partners and stakeholders, continuing work on restoration sites where we’ve funded beaver dam analogues and continuing to lay the groundwork for re-introduction of beavers in areas where it may have ecosystem benefits. Scientists are confident that beaver restoration has the potential to be a nature-based strategy that can aid in reducing wildfire risk, mitigating drought and combating climate change. It’s another piece of the puzzle as CDFW works to implement solutions to some of our greatest environmental concerns,” said Bonham.

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Media contact:
Ken Paglia, CDFW Communications, (916) 825-7120

An Op-Ed by Charlton H. Bonham, Director of the Department of Fish and Wildlife

Beavers are having a well-deserved moment in the discussion around climate solutions.

Healthy beaver populations improve their environment in so many ways – from reducing wildfire risks, to making water conditions more hospitable for our native salmon and trout.

In fact, humans have so admired the skilled work of beavers they have spent millions of dollars trying to replicate the benefits they create. As managers of the state’s natural resources, the California Department of Fish and Wildlife (CDFW) is embracing the opportunity to elevate beaver restoration as part of a larger effort to help mitigate the impacts of wildfires, climate change and drought. Thanks to Governor Gavin Newsom’s leadership and the State Legislature, funding for beaver restoration is now part of our playbook, with funds approved in this year’s budget.

The program funds dedicated scientists who, once hired by CDFW, will begin working on projects that help the environment by bringing beavers back to California rivers where they once thrived.

Beaver dams raise groundwater levels and slow water flow. Slowing down the flow allows water to pool and seep, creating riparian wetlands that support plant, wildlife and habitat growth. Another benefit of beaver dams is the rejuvenation of river habitat for salmon and aquatic insects. The dams also improve water quality because they capture sediment, resulting in clearer water downstream.

Additionally, beaver dams help keep groundwater tables high which can help mitigate drought impacts by keeping vegetation green. This effect can also help fires burn less intensely in riparian areas, which, in the long run, can aid streams and habitats in recovering from fires more quickly. These positive ecosystem benefits are especially true in areas where there are intermittent streams or where streams can disconnect. Once beavers build dams in those areas, the habitat tends to hold water more effectively and allows it to percolate into soils.

Unfortunately, beavers were eliminated from much of their range by the late 1800s due to unregulated trapping and habitat loss. Environmental scientists have tried to duplicate the effectiveness of beaver dams utilizing human-engineered structures called beaver dam analogues. Through this, we have learned that human-created beaver dams can achieve similar carbon sequestration and habitat benefits to that of real beaver dams, but at a much higher cost. Nothing’s better than the real thing, and that means bringing beavers back to their historic habitat and teaching Californians how to coexist with the scientifically named Castor canadensis.

California’s next step is to expand partnerships with California native tribes, non-governmental organizations, private landowners, state and federal agencies, and restoration practitioners to lay the groundwork for implementing beaver restoration projects. The new funding will help develop a framework for these beaver relocation efforts. CDFW and its partners are looking at the feasibility of taking beavers from areas where they are causing conflict and relocating them to areas where they would have ecosystem benefits.

CDFW’s new beaver restoration program allows California to advance on all these fronts -- we’re continuing collaboration with partners and stakeholders, continuing to work on restoration sites where we’ve funded beaver dam analogues and continuing to lay the groundwork for re-introduction of beavers in areas where it may have ecosystem benefits. Scientists are confident that beaver restoration has the potential to be a nature-based strategy that can aid in reducing wildfire risk, mitigating drought and combating climate change. It’s another piece in the puzzle as CDFW works to implement solutions to some of our greatest environmental concerns.