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Note: This article is from Conservation Magazine, the precursor to Anthropocene Magazine. The full 14-year Conservation Magazine archive is now available here.

Chasing Rainbows

November 22, 2011

How unbridled love for a beautiful trout led to ecological heartache

By Anders Halverson
Illustration by Jeanette Jobson

John Muir, the pioneering wilderness advocate, liked to call California’s Sierra Nevada “the Range of Light,” and once you’ve experienced the luminous granite, sparkling waters, and brilliant sunlight of the high country, it’s hard to think of those mountains in any other way. Thousands of lakes punctuate the range, providing a powerful draw for hikers and anglers alike.

Several years ago, I visited one of those lakes with some seasonal employees from the U.S. Forest Service and the California Department of Fish and Game. Covering about 20 acres in a high basin not far from Yosemite National Park, the lake was so clear that you could see the bottom 50 feet below. It was a stunning place. Its name, though, has to remain confidential. That’s because the “seasonals,” as they are known, were on a controversial mission: to tend a network of nearly invisible, monofilament gillnets that they had installed to kill the resident rainbow trout.

It was an ironic situation. That’s because for decades prior to 2001, the fish and game department had been stocking those same rainbow trout into the lake every other year. Those transplants were just a small part of an extraordinary, century-old, fish-rearing effort that has made Oncorhynchus mykiss—a sleek, iridescent, freshwater fish native to cold waters of the Pacific Rim from Mexico to Kamchatka—one of the world’s most widespread exotic species.

Since aquaculturists first figured out how to artificially spawn and raise trout in hatcheries in the 1850s, billions of rainbows have been dropped into lakes and streams in every U.S. state and on every continent except Antarctica. Today, U.S. agencies typically release about 100 million rainbows annually in a bid to make sure anglers don’t go home with empty creels. That’s about 25 million pounds of trout dumped into America’s freshwaters each year—enough to give every household the makings of a nice meal and support a multibillion-dollar sportfishing industry that is a potent economic force in some regions.

The rainbow’s rise, however, has had far-reaching ecological consequences. Rainbows often spawn with native fish such as the cutthroat trout of the American West, hybridizing pure populations out of existence. They are vectors of disease, tough competitors, and fearsome predators that can wreak havoc on wild fish and other fauna. Release rainbows into an isolated, historically fishless pond such as the one I visited in the high Sierras, and you can usually bid native frogs and other amphibians good-bye. As a result, in certain waters in California and elsewhere, agencies that once worked to spread rainbows far and wide are now struggling to turn back the clock by eliminating them. In the process, they’re rekindling fierce conflicts over what should live in our lakes and streams—and who should decide.

Getting Over the Rainbow
Although the gillnets had hung under the ice like curtains all winter, we found only a few four-to-five-inch rainbow trout in the nets, in various stages of decay. This, I was told, was now typical at this lake, suggesting not many fish remained.

That was good news to the leaders of the elimination effort. To the Americans who first visited the area in the late nineteenth and early twentieth centuries, however, a lack of fish would have meant the lake was being wasted. And so miners, explorers, and recreational groups such as the Sierra Club—and ultimately the state fish and game department—started hauling fingerling brook, golden, and rainbow trout up into the mountains on mules and in backpacks, in milk cans and coffee cans.

No matter how much stocking was done, however, it was not enough to satisfy some visitors. “The fact that most of these waters have continued barren of fish life has caused comment by the many tourists and campers who annually visit this wonderland,” one Fish and Game employee noted in 1929. Little could he have known how much progress the department would soon make. With newly developed, aerial fish-stocking techniques, the department carpet-bombed the lakes with trout after World War II—a pattern repeated throughout the western U.S. Just five percent of the West’s thousands of high mountain lakes contained fish a hundred years ago, according to one estimate; today, about 60 percent have fish.

There were surprisingly few objections to the transplants. Environmental groups such as the Sierra Club seemed to take their cue from Muir, who encouraged stocking because he knew it would create a constituency for the region. Stocking, he wrote in 1901, “will become the means of drawing thousands of visitors into the mountains . . . Trout-fishing, regarded as bait for catching men, for the saving of both body and soul, is important, and deserves all the expense and care bestowed on it.” Although the naturalist Joseph Grinnell noted as early as 1924 that stocking was affecting amphibians and other lake inhabitants, few scientists studied the high mountain lakes and there was almost no research into stocking’s effects or effectiveness. For the most part, it seems to have been a case of “out of sight, out of mind.”

The Department of Fish and Game, meanwhile, had little incentive to study the impacts of its expensive and widespread program. By the 1960s, the agency had millions of dollars invested in airplanes and hatcheries, numerous employees who depended on the program, and the backing of political heavyweights and a public to which it had long promoted the virtues of stocking. When Phil Pister, a now-retired agency biologist, proposed evaluating the impact of aerial stocking in the 1970s, he got a call from his chief in Sacramento. “I agree you ought to do this,” he recalls the chief saying. “But the director does not want to hear that his personal airliner is going to be grounded because we can’t plant fish with it anymore. The best thing to do is just to forget this.” The fish-stocking plane, Pister recalled, was a gorgeous Beechcraft King Air that was a popular means of transport among state officials, including the governor. He dropped the idea.

Snorkeling for Tadpoles
The situation began to change in 1995, however, when Forest Service officials began rewriting their management plans for some of the wilderness areas that Congress had created in the Sierras. They became particularly concerned about the fate of the mountain yellow-legged frog (Rana muscosa), a medium-sized brown frog endemic to the mountains of California and Nevada. It was once the most common amphibian in the Sierra Nevada—so abundant that in 1915 a survey team reported that they could not help stepping on the frogs as they navigated their way around some lakes. By the end of the twentieth century, however, one researcher estimated the frogs were present in fewer than 15 percent of the lakes they had once occupied. Some studies suggested that stocking might be to blame, while others fingered pollution or pesticides drifting in from the Central Valley.

To help clarify matters, the Forest Service hired Roland Knapp, an ecologist at the Sierra Nevada Aquatic Research Laboratory, to survey alpine lakes in places such as the John Muir Wilderness and the Ansel Adams Wilderness. Fish and Game officials “were sort of indifferent to the work,” he recalls. “They were basically saying, ‘Yeah, you can have permits, but it really doesn’t have any bearing on what we are doing, because there are no effects.’”

When he started, Knapp expected to look at 500 to 1,000 lakes over a couple of years. Instead, over the next ten years, his team surveyed every water body between Mount Whitney and Yosemite big enough to show up as a blue dot on topographic maps—about 7,000 lakes and ponds in all.

These were not cursory surveys. The researchers tallied the size and depth of the bodies of water, counting amphibians, reptiles, and invertebrates. If the lake was deep enough to hold fish over the winter, they went snorkeling and laid out gillnets to study the species composition and structure of fish populations. Knapp and a colleague also had funds to do some experimental work on the effects of fish. In a remote basin, they used gillnets to remove fish from five of eight lakes and then watched to see what would happen. The results left little doubt: fish and frogs didn’t mix. Frogs were seldom found in lakes containing fish, and when the fish were removed, the frogs often made a dramatic comeback.

One summer, Knapp took me to visit one of these transformed lakes. On the hike in, I saw no amphibians in any of the many bodies of water I passed. But around that lake, the frogs were thick—hopping from underfoot at the last possible moment. Tadpoles clustered in warm water along the edge, so many in places that they obscured the mud below. About 2,000 adult frogs lived in the lake, Knapp told me, a dramatic increase over the 20 or so that had lived there before the fish were removed. (I’ve since learned that, more recently, a deadly fungus has hit frog populations hard in some of these areas, posing a new setback.)

Exactly why fish cause frogs to disappear is not entirely clear. The trout might spread disease, or they might outcompete the tadpoles for food. Most likely, though, the mechanism is more direct: the fish eat the amphibians. With the frogs having evolved over the past 10,000 years in blissful ignorance of fish, it is no surprise that they are so vulnerable to these fearsome omnivores. In addition, the mountain yellow-legged frog is a particularly aquatic species, making it more vulnerable to fish. The adults are seldom found more than a couple of hops from a lake or pond during the summer, and they spend their winters in the water under the ice. More important, the tadpoles spend at least two years in the lakes before they metamorphose. This means the tadpoles can live only in deep lakes that do not freeze all the way through—the same lakes that were most commonly stocked.

It was not just frogs that had been affected, Knapp found. At another lake from which fish had been removed, Knapp showed me a larval mayfly, Callibaetis ferrugineus. It had been absent when the lake contained fish; but by time I visited, the lake bottom had between 100 and 500 in every square yard. The total number of species in the lake had increased tenfold, Knapp said—and the total biomass of the invertebrates had increased by a factor of one hundred. Changes in lake life, he noted, could also ripple out to other animals, such as insect-eating bats and birds.

Even lakes that had never been stocked could also feel an impact, the studies suggested. Amphibian populations naturally fluctuate widely, for instance, and occasionally the number of frogs in a lake is bound to drop to zero due to chance alone. Under normal circumstances, the lake will be recolonized by frogs from a neighboring population. But if frogs are eliminated in neighboring lakes due to the presence of fish, then the fishless lake won’t be recolonized.

Who’s This Crazy Scientist?
Knapp’s data also highlighted something that made Fish and Game officials sit up and take notice: the fish populations in many of the lakes were probably self-sustaining. Although the department had stopped stocking the lakes that Knapp’s team was studying, in many of them the surveyors still found fry. Since the little fish did not come from a plane, they must have come from natural reproduction. Based on these preliminary data, the department agreed to stop stocking 60 lakes for five years, to determine whether the fish populations could in fact sustain themselves. The experiment showed conclusively that about 70 percent of the lakes that the department had been stocking for 50 years or more held self-sustaining trout populations. In other words, the agency had, at best, been throwing money away—up to $1 million a year, according to Knapp. At worst, the stocking may have made fishing worse by creating lakes full of stunted fish.

“As soon as those results began to come in, [the department’s] posture became much more defensive,” Knapp told me. The reaction, at least among a certain portion of the department, was something along the lines of: “How can this be? How can you be seeing all these effects? Something must be wrong . . . who’s this crazy scientist that’s coming in, telling us that these fish are doing bad things to the backcountry?”

That was the low point of his relationship with the department, Knapp recalled. Nevertheless, there was some cautious interest in his work. For one thing, department officials worried that they would lose control of the stocking program if the federal government were to list the mountain yellow-legged frog as an endangered species. If the state could show that it was helping the frogs to recover by removing the trout, however, it might avoid a listing. The economic argument against stocking also proved compelling. Soon, officials had drawn up internal regulations that put a stop to stocking lakes with self-sustaining fisheries. By 2001, a department that had once stocked more than 1,000 lakes in the Sierra Nevada every year was stocking fewer than 20. Money once spent on stocking went toward surveying the lakes that Knapp and his crew had not yet visited. And, perhaps most significantly, the department began drawing up plans to eradicate trout from some of the lakes that it had been stocking only a few years earlier.

A Big Shift
Today, about 20 lakes in the eastern Sierra are newly devoid of fish, and just the existence of an eradication program represents a monumental shift in the stance of fish and game managers. “The thinking back in the ’60s . . . particularly in the state agencies, was: ‘If you can’t catch it and eat it, the hell with it,’” Phil Pister told me. “Back then, the entire effort in virtually all fish and wildlife agencies in the West, especially in California, was to provide sportfishing.”

Now, the California Department of Fish and Game employs dozens of nongame biologists and allocates by far the biggest portion of its funds to biodiversity conservation. And it’s not just California. Most other states have undergone similar shifts. Fish removal and restoration projects are planned or have already occurred in states from Idaho to North Carolina. Federal agencies such as the National Park Service and the U.S. Fish and Wildlife Service, which spent much of the first half of the twentieth century stocking rainbows into waters that had never seen their kind before, are today taking a leading role in removing them.

Partly, no doubt, this shift has occurred because of individuals such as Pister and Knapp. It also has been driven by the threat of federal intervention: fish and game commissions in California and elsewhere have been forced by elected officials to take action to protect those species at risk of ending up on the Endangered Species list.

Finally, though, society as a whole has undergone a dramatic shift. Nongame species have developed a large constituency. Groups dedicated to the preservation of native wildlife have boomed in the past several decades. Bird watching and other forms of outdoor recreation that do not depend on hooks or bullets have grown. And at the same time, the popularity of sportfishing and hunting has leveled off. The total number of fishing licenses sold in California, for example, peaked in 1981.

Such shifts have spurred controversy and division within state wildlife agencies. Although employees of the California Department of Fish and Game were hesitant to acknowledge it, there seems no question that the fish removal program generated conflict. “This was hard,” Pister told me, “particularly for the pilots. You know, these guys, they work their heads off and make sure that they’ve planted all the lakes just right—did everything according to protocol. And then all of a sudden, you say: ‘What you guys have been doing, it doesn’t do any good.’”

The change also has not been popular with anglers and hunters, the traditional constituents of fish and wildlife agencies. For one thing, they supply most of the funding for these agencies through license fees and taxes on sporting goods, and some don’t think it is fair that their money is now being used to conserve nongame species. And, ironically, anglers are now being forced to fund the eradication of a fish many like to pursue.

If the anglers are unhappy, however, then many of the business owners who depend on them are nearly apoplectic. Take, for example, the situation in Bridgeport, California. Like many towns on the eastern side of the Sierra, Bridgeport depends heavily on recreation, especially on the millions of anglers from central and southern California who come to fish nearby reservoirs, lakes, and streams. I visited Bridgeport after one of my trips into the Sierras, and when I casually described the fish and game department’s gillnets to the owner of my hotel, I got an earful. “Idiots,” “stupid blunders,” and “stepping on their own toes,” are some of the choice words scrawled in my notes. And as I walked around town the next day, talking to the owner of the fly shop, my server at the diner, and others, it quickly became apparent that his sentiments were widely shared. From what I could tell, the local business owners and residents were upset (1) because the department was removing fish, (2) because they heard about it from an outsider like me, and (3) because they feared the public would think twice about going on an expensive fishing trip in a region where fish were being actively eradicated. “You get one bad story about fishing, and people will go somewhere else,” one local told me.

How did the Department of Fish and Game respond? I called Curtis Milliron, who supervised the fish-removal program in the eastern Sierras for the agency, and began asking about the “eradication program.” He calmly and professionally sought to set me straight. Fish removals, he told me, were but one small part of a new way of managing the region on the basis of aquatic biodiversity management plans—blueprints that seek to balance recreational fisheries with the needs of native species. Sure, the mountain yellow-legged frogs and Knapp’s work had kick-started the program, he told me. But the department was not just running around, killing fish in some haphazard attempt to save the latest poster species for the Endangered Species Act. These were carefully thought-out plans based on mountains of data.

The department hadn’t publicized the specific lakes in which the removals were occurring because it feared sabotage, Milliron added. In fact, some gillnets had been destroyed, apparently by someone who did not want the fish removed. But Milliron feared the bucket brigade even more. It would be a simple matter to catch a few fish from another lake, put them in a bucket, and carry them over to one of the lakes in which fish had recently been eradicated. Natural reproduction would quickly destroy all of the department’s efforts.

It’s not an implausible scenario. Such illegal fish introductions have become increasingly problematic around the U. S. And, as Milliron pointed out, that is exactly how entire basins in the high Sierra Nevada became populated with fish only a hundred years ago.

But nobody need fear for the quality of the fishing in the eastern Sierra, Milliron argued. For one thing, eliminating fish from all the high lakes would be physically and politically impossible. At an absolute maximum, the department planned to target only about 150 of the 700 lakes in Milliron’s purview that currently hold fish. And even getting to that number was unlikely any time in the near future without an unlimited supply of money and personnel.

In truth, it’s the same story throughout the country. Fish-removal projects are occurring everywhere, often with lots of publicity. But if you compare the waters from which fish are being removed with the waters where they have been introduced and have established self-sustaining populations, it’s just a drop in the bucket. Rainbow trout, it seems, are here to stay. ❧

–Anders Halverson is a journalist with a Ph.D. in aquatic ecology from Yale University. He lives in Boulder, Colorado. This article is an adaptation from his recent book An Entirely Synthetic Fish: How Rainbow Trout Beguiled America and Overran the World, published by Yale University Press. Find photos and resources related to fish-stocking at

Artwork: Camouflaged Rainbow, ©Jeanette Jobson
Collection of Provincial Art Bank, Government of Newfoundland and Labrador

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