Anglers across the West love to fish in high, alpine lakes, and Wyoming’s Wind River Range is nearly unbeatable for this experience. Around this time of year, frost covers the tips of trees at sunrise, and there’s plenty of room along the lonesome blue waters above 10,000 feet.
Those who do make the trek – which usually takes more than 15 miles of hiking – are greeted by hungry golden, brook or cutthroat trout looking to fatten up for the winter. They’ll take almost any fly, from a yellow foam grasshopper, to a Parachute Adams to a tiny ant. And the fish are often big, colorful and photogenic.
But as untamed, historic and relaxing as a day on the water feels, it’s anything but natural.
New research is shedding light on how the history of fish stocking has impacted alpine lake ecosystems in the Wind Rivers. In many cases, the genetics of trout have evolved rapidly, allowing them to survive in harsh mountain environments.
Starting in the 1800s, individuals, sporting clubs and government officials began stocking ponds and lakes in the Rocky Mountains with trout. Jen Brown, a university professor who wrote “Trout Culture,” a book on the subject, said many of these waterways didn’t have any fish in the first place.
“When Western settlement started occurring, settlers brought along their sport fish,” she said. “It's a nice backcountry survival food. They're pretty easy to catch. And they bring sport. They'll bring people who want to go up into the mountains and then give them something to do while they're there.”
In the first few decades, people would carry milk cans full of fish on their backs or strap them to horses. In the Wind Rivers, this was largely done by one man who ran a fishing outfit in the area. Nowadays, game and fish departments across the Mountain West usually use trucks or aircraft to dump fish into lakes.
“We think of the West and fly fishing in the West as this very pristine activity, one that is out in the wilderness and untouched by humans,” Brown said. “But in reality…those fisheries and those trout only exist through widespread manipulation of the environment.”
The manipulation of fisheries has had some consequences. Brown said that in some cases introduced trout pushed out native fish populations. Research suggests stocking has also hurt invertebrates that previously had few predators, as well as amphibians like frogs. Beginning in the 1960s, wildlife managers became more cautious with how much they impacted waters.
“And that's actually worked really well, at least in terms of populations that are already self-sustaining,” Brown said.
But the history of stocking has still led to some interesting scientific consequences.
In a lab at the University of Wyoming, professor and evolutionary ecologist Katie Wagner has jars full of fish she helped catch with gill nets in the Wind Rivers. She’s been examining trout under a microscope to compare fish species stocked more than a century ago with hatchery fish.
Lakes in the region are usually iced over for more than half of the year, and there is very little plant life for trout to feed on. Survival is challenging in such an extreme environment.
“Having fish in these lakes is having a really big ecosystem consequence,” Wagner said. “How is that feeding back onto the fish themselves? How is that impacting their own resource? And their survival?”
What the team found – and recently published – was a case of rapid evolution. Trout developed physical attributes in their gills in just a few decades. Fish use gill rakers to filter prey such as plankton, and the more they have, the easier and more efficient it is for them to eat.
“In populations that were stocked 50 or 100 years ago, we have more gill rakers than in populations that were stocked recently or that we look at from the hatchery,” Wagner said.
This is notable because most people think evolution takes thousands or millions of years, she added. “The idea of putting fish into these really extreme and novel environments, and watching them change over the course of a human lifetime is an exciting finding.”
Researchers hope to continue to study how alpine lake fish stocking has impacted mountain environments. Wagner wants to keep looking at genetics to compare trout populations that survived in the Wind Rivers to ones that didn’t – and the differences in their environments and physical appearance.
For Lucia Combrink, lead author on the study, the research has another takeaway. In the face of declining global biodiversity, this could show that life will find a way to survive – even under extreme stress.
“It's an example where we see rapid adaptation. And that's hopeful for other examples where we hope that natural populations can have what they need to persist,” Combrink said. “Even in the face of major change.”
This history of ecological change – and how humans played a part in it – is a meaningful subject to think about while casting on the shores of the seemingly untouched western alpine wilderness.
Editor's Note: An earlier version of this story described frogs as "reptiles." They are, in fact, amphibians. The copy has since been updated.
This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, KUNC in Colorado and KANW in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.
