Rare Paiute cutthroat trout reintroduced to native habitat, a 30 year saga for Bill Somer

by Brian Bahouth

A Paiute cutthroat trout is reintroduced into its native habitat - image - California Department of Fish and Wildlife

Bill Somer is a senior environmental scientist for the California Department of Fish and Wildlife. In 1988 he joined the effort to reestablish the threatened Paiute cutthroat trout. Somer became project leader in 1993. With the advent of genetic technology, Somer and team were able to precisely identify pure Paiute cutthroat trout from hybrid and nonnative species and successfully bring the rarest trout in America back from the edge of extinction.

Last week after decades of work and travail, 30 Paiute cutthroat trout were released into their native habitat, an 11 mile reach of the Silver King Creek.

The Silver King Valley is north of Yosemite in the Carson-Iceberg Wilderness and roughly 20 square miles in size. The valley is home to a handful of creeks where the Paiute cutthroat trout now lives free of invasive species since unauthorized releases of other species of trout in the early 1900s. Just ahead on this edition of the Wild Hare podcast, we speak with veteran wildlife biologist Bill Somer …

See music credits below text.

The Silver King basin – image – California Department of Fish and Wildlife

Officials ended recreational fishing in the Silver King drainage in 1934. Over time, sheep and cattle grazing further degraded the Paiute cutthroat trout’s habitat. Competition with nonnative species combined with grazing to threaten the fish with extinction. Bill Somer explains the problem.

“The nonnative fish have come from our stocking of this over the years. One of the biggest culprits of the Paiute was the introduction of rainbow trout, and even restocking Lahontan cutthroat back then on the historic ranch. The rainbows aren’t from very far away just the other side of the Sierra really. In other places, brook trout have been a big culprit that were stocked from the East Coast from various waters. They’re adapted to different climates. Sometimes it’s an advantage to them, sometimes not. Sometimes they can out compete and prey upon the native fishes and pretty much exclude them from their habitat that way.”

Map – California Department of Fish and Wildlife

The ability to accurately identify pure Paiute cutthroat trout from other hybridized fish was a transformative development for Somer and his team.

“The science has evolved as well over time as far as how we can … what tools we have available to use to separate and identify unique characteristics among these fish. Back when I started, a lot of genetics was still just kind of relying on looking at proteins. Before then they looked at just the traits of the fish. In other words, the Paiute cutthroat generally are characterized by having few or no body spots, kind of a purplish hue coloration.

“Adult fish have these what they call par marks, a kind of blotchy spots, large spots on their side, even as adults, and other fish generally, other trout generally tend to lose them as they mature. They’re most closely related to the Lahontan cutthroat, which is very heavily spotted.

“So that was actually used as one of the first criteria, but now we have pretty powerful advanced genetic techniques to be able to tell pure Paiute from one that’s interbred or intermixed with other fishes. A big problem we’ve had over the years since officials first described (the fish) was introductions of nonnative fish that competed and interbred with the Paiute cutthroat trout. We’ve been working ever since then to try to restore the pure fish back into the drainage. This most recent effort was, I think, pretty cool because we actually were able to restore the fish back to its historic range. The fish will actually  occupy more habitat than it did historically.”

A Paiute cutthroat trout – image – Bill Somer, California Department of Fish and Wildlife

The Paiute cutthroat trout is related to the Lahontan cutthroat trout. Somer says, genetic analysis has not just enabled the more precise identification of the Paiute cutthroat trout from nonnative species but genetic techniques have also deepened knowledge about the history of the threatened fish.

“One thing we’re learning is that the time span on this is perhaps much longer than we originally thought. The Lahontan colonized the Lahontan basin millions of years ago, and it used to be thought that the Paiute cutthroat were isolated from Lahontan like 8,000 years ago. Recent genetic studies suggest that it might be much longer than 150,000 (years) to perhaps as much as over 500,000 years ago.”

Somer said efforts to remove nonnative species from the Silver King drainage had been underway since the 1960s. He came up with the idea for the current plan to reestablish the fish while hiking in the Silver King valley with a fellow biologist. Basque sheepherders had moved some of the fish outside their native rage, upstream of Llewellyn Falls. On his hike, Somer realized the falls formed a barrier that trapped a pristine community of Paiute cutthroat trout upstream, and he was correct. Only a couple hundred pure Paiute cutthroat trout remained on earth.

“Back in ’94, I and another biologist hiked through the canyon, the Silver King Canyon. We found a series of waterfalls and we thought that nobody had done that before. So we kind of identified the lower barrier, the lower range of the fish, and that kind of started the concept of this project now.”

The California Department of Fish and Wildlife, the US Forest Service, and the US Fish and Wildlife Service moved some of these fish to other fishless, protected streams within the Silver King watershed as well as four watersheds outside the Silver King basin in an effort to stave off extinction and develop a stock to use to repopulate the native habitat once all the nonnative species were removed.

Wildlife officials proposed to use a piscicide known as rotenone to rid the Silver King Creek and its tributaries of nonnative fish. The Laboratory Chemical Safety Summary Datasheet (LCSSD) lists rotenone as an acute toxic, irritant and environmental hazard. Its use in the valley was controversial and garnered a decade of legal challenges. Wildlife officials ultimately prevailed in court, and from 2013 to 2015 treated the Silver King Creek and its tributaries with rotenone. Somer and others spent the following 3 years monitoring the creek to ensure all the nonnative species were gone.

According to the LCSSD, rotenone is an “odorless, colorless, crystalline isoflavone used as a broad-spectrum insecticide, piscicide, and pesticide. It occurs naturally in the seeds and stems of several plants, such as the jicama vine plant.” Somer said the use of rotenone was tightly controlled and monitored and is only used when absolutely necessary to prevent extinction of rare species or other ecological catastrophe.

“Rotenone leaves the system in a matter of hours. It gets washed downstream but it’s also breaking down with sunlight and biological processes. At the lower end of the project, we set up a detoxification site or neutralization station and applied potassium permanganate, an oxidizer, to detoxify the rotenone.

“We worked really closely with the Lahontan regional board. We spent $30,000 a year on water quality monitoring to make sure that everything was where we needed it to be in terms of concentration. It was a very tightly controlled treatment.

“Then we spent three years just evaluating the success of that treatment. We had crews go out and take water samples every 100, 150 meters throughout the whole basin. It was like 200 samples, 190-ish samples a year. We had crews go through with electro-fishing gear to look around to see if they find any bad or nonnative fish. We did that in ’16, ‘17 and ’18, so we did a pretty thorough evaluation before we started retreating.”

Silver King Creek – image – California Department of Fish and Wildlife

For biologist Somer, removing the nonnative species was the most difficult aspect of the restoration.

“The hardest part is the removal of nonnative fish. That can be a pretty stressful time, especially just doing the job but also some of the politics involved. This stage of the project is really more of the fun and positive part of it. Hopefully everybody can support this at this time. We try to do as much as we can to make sure that some of the unique characters of the fish are not lost along the way when restocking, and that may be one of the trickier parts of this, but some of it is really out of our control … the fish will do what they will do, obviously.”

Mule transported Paiute cutthroat trout from a source population in Coyote Valley Creek 2 miles to Silver King Creek – image – California Department of Fish and Wildlife

The 30 Paiute cutthroat trout reintroduced into Silver King Creek on September 18 were collected from a source population in the in Coyote Valley Creek about 2 miles away and transported by mule to the Silver King Creek.

By virtue of establishing source populations in creeks adjacent to the fish’s native habitat, the amount of habitat available to the fish nearly doubles, and according to Somer, genetic diversity is key to the fish’s long-term survival and possible delisting as a threatened species. Moving forward, Somer and others will restock the native habitat from all the different source populations wildlife officials have established to help develop a robust genetic basis for the repopulation.

Nothing happens fast when it comes to reestablishing a native species. Bill Somer has the patience of a wildlife biologist. He described something of an ecological balancing act that needs margin enough to be prepared for fire, drought and other potential stresses on the fish populations.

“Restocking after a chemical treatment to remove nonnative species can take a series of years, especially because we have so few fish to work from. We take small numbers and restock into the stream and slowly build a population because we don’t want to impact source populations either, reducing their genetic fitness by taking too many fish out of the population. So that’s why we only took 30 fish out of the Coyote Valley this year and stocked them in Silver Canyon, Long Valley.”

Music Credits in order of appearance as reported to the Public Radio Exchange:

Song: Greenland
Artist: Emanicipator
Album: Safe in the Steep Cliffs
Label: Loci Records
Year: 2010
Duration: 1:25

Song: Aurora
Artist: Jon Hassel
Album: Last Night the Moon cam dropping Its Clothes in the Street
Label: ECM Records GmbH
Year: 2009
Duration: 2:46

Song: Lerandis
Artist: Cluster
Album: Qua
Label: Nepenthe Music & Publishing
Year: 2009
Duration: 1:15

Song: A Valentine Out Of Season
Artist: Stephen Drury
Album: In a Landscape: Piano Music of John Cage
Label: Catalyst
Year: 1944
Duration: 4:07

Song: White City
Artist: Sounds from the Ground
Album: High Rising
Label: Waveform
Year: 2006
Duration: 1:37

Song: Sybarite
Artist: Solid Doctor
Album: Beats Means Highs
Label: Declasse
Year: 1996
Duration: 1:46