From Stream to Summit: the Natural History and Conservation of the Lahontan Cutthroat Trout

There is a giant in the waters of the Lahontan Basin; a beast so large it's fabled that settlers could walk across its back. Lucky is the person who catches a glimpse of the colorful mass of muted green and orange scales hidden among Nevada’s lake-dwelling organisms and vegetation. This elusive creature is none other than the Lahontan cutthroat trout (Oncorhynchus clarkii henshawi, abbreviated as LCT). Ranging from five to ten pounds and with a record of a whopping forty-one, this fish is considered to be the largest subspecies of cutthroat trout—a giant indeed. The species’ massive size is an homage to its ancient origins: once dwelling in the Pleistocene waters of the gargantuan Lake Lahontan, its habitat has now been whittled away to the various lakes, rivers, and streams of greater northwestern Nevada [1]. Like many native species, this trout and its habitat share a deeply intertwined history of ecological change, adaptation, and persistence. There is a beauty in this species’ obscurity—like the quiet allure of the desert’s muted watercolor landscape, it takes a certain eye to appreciate the unique beauty of an endemic species in its native environment. But, Lahontan cutthroat trout may face the same fate as their prehistoric home: just as Lake Lahontan’s enormity dwindled away, so might the species itself—and we’re already starting to see it happen.

It seems redundant to mention humanity’s impact on the earth and the species that call it home. The ruinous hand of the Anthropocene finds its way even to the isolated desert, its power strong enough to lead the waters astray and disturb thousands of years of instinct. But it wasn’t always like this—change is to be expected, needed even. The natural fluctuations of temperature, the ebbing and flowing of water levels, were the impetus for Lake Lahontan’s pre-humanity fragmentation—but the current rate at which the earth is changing is unprecedented. Any drastic alteration of a landscape is devastating to an ecosystem. It’s not just the parching of the earth from drought or the decreased rainfall that turns gushing streams into a mere trickle; early snowmelt triggers a deluge that can be equally damaging to river systems [2]. This is especially significant for Lahontan cutthroat trout, a species that depends upon the rising and falling of water levels to guide them to spawning grounds. Disturb this, and shockwaves ripple throughout the entire ecosystem.

You can’t force evolution—it’s a long, tedious process, spurred by seemingly miraculous random mutations that, with the right conditions, may result in speciation. This is what happened to Lahontan cutthroat trout. As fragmentation slowly occurred, the species was able to adapt to the new niches carved out by the formation of streams and tributaries, each of them utilizing their environments to develop distinct reproductive strategies. Let’s take, for example, the adfluvial variety of LCT. This particular reproductive strategy makes use of the branching tributaries by using them as spawning grounds. From April to July, these fish migrate from their lake homes to lay eggs in the winding offshoot streams, a journey that will be later repeated by their offspring. While adfluvial trout bounce between lakes and tributaries, fluvial trout move from tributaries to bigger rivers after maturing. Alternatively, the resident-type Lahontan cutthroat trout lives and spawns in the same lake in which it was born. This is why the rapidly changing hydraulic regime is so concerning—for the fish that have modeled their reproductive strategies off of the unique water flow pattern in their environment, even slight temporal changes can completely disrupt spawning times and alter the success of their offspring. 

The habitat disturbance doesn’t stop there: through the construction of dams, alteration of waterways, and introduction of non-native fish, humanity has directly changed the natural environment of the Lahontan Basin [3]. To more efficiently supply water to the Lahontan Valley, waterways connected to the Lahontan Basin have been altered and rerouted. Giant gray dams shoot up imposingly from rivers and into the sky, leaving a wake of foamy, gushing water, an attempt to manipulate and control the river to our advantage. This process exacerbates the already harmful effects of drought and climate change by providing yet another physical setback for LCT: it’s like if someone built a wall right in the middle of your street. To adfluvial and fluvial trout, this blockage is extremely detrimental to their entire life history. The large, concrete mass is a physical barrier to spawning grounds, further lowering reproductive rates. 

Lahontan cutthroat trout aren’t the only trout found in the desert’s watery depths. In order to encourage recreational fishing in the Lahontan basin, species like rainbow and brook trout were moved from their native homes on the East coast and deposited into the arid, desert lakes and streams of Nevada—quite a dramatic switch. Introducing non-native species is rarely a good thing: time and time again, the horror story of a species being introduced to an area, subsequently invading it, outcompeting the native species, and destroying the habitat unfolds. This is exactly what happened to our Lahontans with these two new introductions. 

However, most of the pressure doesn’t come from competition with resources—no, it comes from the interbreeding of native and non-native trout, resulting in hybrid offspring that dilute the genetic integrity of LCT. It’s reverse speciation in action. What once was a biodiverse lake with an abundance of species, each of which has its own specific niche or role, may become a monolith of fish all competing for the same resources. But the risk doesn’t just end there: hybrids are observed to have reduced fitness, rendering them more susceptible to environmental stressors [4]. There’s more to biodiversity than just its intrinsic value. A small, homogenous population—and a sensitive one at that—is at an increased risk of extinction due to the lack of genetic diversity. Say some type of natural disaster happens, altering the salinity levels of the lake. With enough genetic diversity, there’s a decent chance that some particular allele will grant unique desensitization to salinity—this individual will survive, hopefully pass on its traits, and the population has a chance at recovery. But without this variety, a single disastrous event can wipe out entire populations.

Perhaps the most impressive thing about Lahontan cutthroat trout—other than their size—is their resilience. There’s a spot along the Marys River in Nevada where the river flattens out and flows into the valley, where little residual pools are left when the water evaporates. Even here, these fish persist. Jason Barnes, a Trout Unlimited biologist and Lahontan cutthroat trout expert, described to me the trout’s incredible ability to survive in the most unlikely of habitats: “one hundred degrees outside, tiny isolated pools that haven’t seen surface waters in a month, 10-12 feet long and 6 feet wide, full of fish.” These are the very same fish that live where the snowy slopes of the Sierra Nevada reach down and touch the high desert, where lakes freeze over until March. “[They] can tell the difference between 0 degrees Celsius and 4 degrees Celsius,” says Barnes. There’s nothing more incredible than nature’s connection, the way species are fine-tuned to their environment. These fish have the innate ability to know the exact conditions for spawning: “[It’s] a slow ramp up to the peak, [but] once temperatures become ideal, it’s just a flood of fish coming out of the creek.” 

This is part of the reason why Barnes thinks Lahontan cutthroat trout are so special; they evolved alongside the changing hydraulic systems, rendering them as deeply intertwined in their habitat as the geographical characteristics of the land itself. Though non-native trout have the ability to survive in these areas, there’s no comparison to the Lahontan cutthroat trout’s unique relationship to the water—it’s built on pure instinct, a tried and true method that has worked for millennia. “One of the greatest parts about LCT is that they could exist in places where most trouts wouldn't have a chance in hell,” Barnes remarks.

But the relationship between trout and the land is not the only parallel—the introduction of the previously mentioned rainbow and brook trout has a haunting similarity to the colonization of the West. As settlers trudged westward, the dusty, sagebrush-covered landscape of Nevada was unsurprisingly a stark difference from the lush forests of the East. Longing for some semblance of home, brook trout were brought over in order to infuse their culture into a new area—it’s a kind of cultural imperialism, Barnes says. Lahontan cutthroat trout hold extremely important symbolism to the indigenous tribes of the area: in fact, many of the tribes of northern Nevada contain some form of “trout-eater” or “fish-eater” in their indigenous names. The invasion of these species into the area reflects the violence of colonialism, the forceful overturning of time-honored practices that seep into the cracks of the earth and foundationally change ways of life, both human and animal. 

Lahontan cutthroat trout are now considered threatened. They have been pushed out of 90% of their native historic range, another casualty in the global pattern of freshwater fish decrease and overwhelming loss of biodiversity [5]. Fish tend to be looked over in favor of more high-profile species, rendering them almost an afterthought in the grand scheme of conservation. It’s almost understandable—Lahontan cutthroat trout are but one fish in one habitat in one part of the world. But still, each organism plays an essential role in its ecosystem: one domino topples, and the rest are doomed to fall. 

However, that’s not to discount the work that is being done to restore LCT populations. The status of Lahontan cutthroat trout has been known since they were declared threatened in the 1970s, but Barnes mentions that “people were raising red flags as early as the 1880s.” Today, conservation initiatives largely revolve around restoring numbers through hatcheries and overall habitat restoration. 

Fieldwork alone is no easy feat—even in the most cushy of environments, it still involves hours of physical labor. But imagine camping out for up to eight days at a time in the desert, facing the burning days and frigid nights with only the supplies you brought in on your back. This is what Barnes does. He and his team pack up everything they need for several days of research and travel, set up base camp, and get to work. A team may go out on a boat with an electrofisher, leaving a trail of stunned fish in their wake ready to be injected with a tracking tag and rereleased, or a group of people may hike for hours with heavy backpacks full of fish; fieldwork takes a variety of forms, each with their own challenges and rewards. 

Maybe the purest form of science is collecting data crouched on the dusty ground or the back of a pickup truck hundreds of miles away from civilization; there’s a special connection that comes with being in the fish’s environment, with being in their territory.

There’s more to being a biologist than just science. Aside from being up close and personal with the fish, Barnes also tackles the more social and political aspects. Conservation requires an immense amount of organization, management, and communication. Under his supervision, Independence Lake—one of the few lakes where indigenous LCT populations persist—is constantly staffed from May to July to control hybrids, a job that the Department of Fish and Wildlife is not able to sufficiently handle alone. The relationship between the government and anglers is a whole other can of worms. 

Fishing is a highly cultural and generational practice. A significant amount of the rural Nevada community has grown up venturing to lakes with family to catch trout, a practice that may seem threatened when considering the conservation initiatives that regulate and limit fishing. There’s a misconception that anglers and conservationists go head-to-head—but this isn’t necessarily the case. Barnes is a particularly staunch supporter of engaging anglers with conservation. Sure, there are those who want to fish for the sake of fishing, who want to catch the biggest trophy they can. But there are also those who are interested in the history of the fish they are catching and want to aid in their conservation—this is the type of fishing that should be encouraged. Barnes considers the government’s stance on angling short-sighted: fish are relocated from hatcheries to lakes with the intent for them to stay, but fishing can be utilized to get rid of hybrids and foster a diverse gene pool with more native integrity. Humans are as much a part of the ecosystem as trees, birds, and—yes—fish. Participating in these customs with the respect and understanding they deserve is of the utmost importance to Barnes: “If you can restore that connectivity, you can really get a sense of how things used to be.” 

Tucked away in the halls of one of the buildings at the southern end of UC Davis lies the Genomic Variation Laboratory, the premier facility for Lahontan cutthroat trout research at the university. Parts of the fish are scattered all about the room: bits of fins carefully folded away in envelopes, DNA incubating in tubes, colorful posters on the wall illustrating the native trout of California. Though the lab is approximately 150 miles away from the trout’s habitat, there’s important work being done here. This is where we get to the nitty-gritty of conservation, where we look deep inside the fish, straight to its DNA to uncover information that is invisible to the naked eye. 

Molecular ecology is not an easy thing to wrap your mind around. How is it that so much information is stored away in such a microscopic molecule, spirals upon spirals of complex and intricate segments that hold what is considered to be the code of life? It’s almost overwhelming, how something can be so minuscule yet so enormously important. 

As an undergraduate research assistant, my job is to get the DNA out of samples—a process called DNA extraction. Donning my lab coat, I cut away at fins and place them into tubes, perhaps the closest I will ever get to actual contact with Lahontan cutthroat trout. Colorless buffers are carefully measured and squirted into rows upon rows of samples, each step completing a specific task working at a molecular level. At first, the pipette felt foreign in my hands; it was a tool that I hadn’t used since my junior year of high school, one that was handled with immense care—a real scientific instrument. But that’s what I was doing—real science. This wasn’t a teaching lab; it wasn’t something that I got graded on to train me for the “real world.” This is the real world, and what I was doing had real implications and real effects. 

The first step in DNA extraction is lysis, or the release of DNA. The power to dissolve cell walls lies in the hands of the unassuming proteinase K, a clear, watery solution that is pipetted into the plates of columns. Then, each carefully but scarily similarly labeled container of buffers—Buffer AE, AW1, AW2—is added in consecutive steps to wash away any leftover molecular debris. It’s an extremely methodical procedure—pipette, expel, repeat. The clatter of pipette tips being discarded creates a beat to which I track my progress: one, two, three, four, five. It’s important not to contaminate any sample, but the repetition makes it easy to lose track. After each addition, I carefully walk each plate of samples to the centrifuge, a massive white machine that spins and spins the samples at extreme speeds, the whirring drowning out almost every other sound in the room. The sheer physical force pushes the liquid through filters, where the DNA sticks for good. 

What we are looking for are markers of hybridization. It can be hard to identify a trout solely by looks—but DNA doesn’t lie. Certain single-nucleotide polymorphisms, or SNPs, are fixed within populations; comparing and discerning the genetic differences between Lahontan and rainbow trout is how the SNP panel was created and utilized to identify hybrid samples.

Numbers tell us how much hybridization has occurred within the species, how much genetic integrity is hanging on in LCT populations. After the data is collected, it is quantified and analyzed. This is where we come full circle: the data goes back to management, where it is implemented to further conservation initiatives. Even on a small scale, progress is evident. The 25% hybridization rate in 2015 plummeted to 2% in 2018—an incredible feat for the short period of just three years. 

But conservation doesn’t end with righting humanity’s wrongs. It’s a never-ending process, one of deep, intentional learning and understanding. There’s a difference, Barnes says, driving down a mountain road having been taught about each species of tree, of brush, of grass; knowing that the gentle transition of pine trees signifies a whole new ecosystem. It’s the same feeling with birds, with insects, with mammals, flowers, salamanders, ferns, and frogs. It’s the same feeling with fish. 

Perhaps the Senegalese forestry engineer Baba Dioum said it best: “In the end, we will conserve only what we love; we will love only what we understand and we will understand only what we are taught.”

About the Author: Lila Magbilang

Lila Magbilang is a biological sciences major and professional writing minor at UC Davis. She is interested in ecology, conservation, and genetics, and is pursuing a career in science communication. She has held writing internships at the Smithsonian National Museum of Natural History, UC Davis Coastal and Marine Sciences Institute, and is currently a science writer at The California Aggie. Hoping to shed light on the oft-overlooked species facing conservation issues, this piece was written as an Honors Contract under Prof. Scott Herring. When she’s not knee-deep in science, she’s spending time outdoors or planning her next trip.   

Author’s Note

I wrote this piece for the Honors Contract I did with Prof. Scott Herring during Winter ‘24. My goal was to combine my experience researching Lahontan cutthroat trout in my lab with a broader piece on the natural history of the species. I was interested in telling the story of this animal, as well as using it as a model for organisms that are often overlooked in conservation. As an aspiring science writer, this opportunity was good practice in ironing out my writing voice and producing a more lengthy work on a topic of my choosing. I hope readers are able to visualize and feel immersed in this species’ story, and leave with a greater appreciation of the more low-profile organisms that play an enormously important role in their ecosystems. 

References

1. Benson LV, Thompson RS. 1987. Lake-Level Variation in the Lahontan Basin for the Past 50,000 Years. Quaternary Research. 28(1):69–85. doi:https://doi.org/10.1016/0033-5894(87)90034-2.

2. Campbell T, Simmons J, Sáenz J, Jerde CL, Cowan W, Chandra S, Hogan Z. 2019. Population connectivity of adfluvial and stream-resident Lahontan cutthroat trout: implications for resilience, management, and restoration. Canadian Journal of Fisheries and Aquatic Sciences. 76(3):426–437. doi:https://doi.org/10.1139/cjfas-2017-0483. 

3. Al‐Chokhachy R, Heki L, Loux T, Peka R. 2019. Return of a Giant: Coordinated Conservation Leads to the First Wild Reproduction of Lahontan Cutthroat Trout in the Truckee River in Nearly a Century. Fisheries. 45(2):63–73. doi:https://doi.org/10.1002/fsh.10350.

4. Muhlfeld CC, Kovach RP, Al‐Chokhachy R, Amish SJ, Kershner JL, Leary RF, Lowe WH, Luikart G, Matson P, Schmetterling DA, et al. 2017. Legacy introductions and climatic variation explain spatiotemporal patterns of invasive hybridization in a native trout. Global Change Biology. 23(11):4663–4674. doi:https://doi.org/10.1111/gcb.13681.

5. Peacock MM, Robinson ML, Walters T, Mathewson HA, Perkins R. 2010. The Evolutionarily Significant Unit Concept and the Role of Translocated Populations in Preserving the Genetic Legacy of Lahontan Cutthroat Trout. Transactions of the American Fisheries Society. 139(2):382–395. doi:https://doi.org/10.1577/t09-039.1.2