It's one of the few government programs most taxpayers love. Stocking America's waterways with fish for anglers has a persistent Norman Rockwell kind of appeal, based on the idea that, with a little help, any lake or stream can be a place where your average kid (or grown-up) can toss out a line and just maybe reel in dinner.

Fish stocking is also the basis for a recreational fishing economy worth $25.7 billion a year, according to a 2011 survey by federal agencies. Hence, it has been government policy since the late 1800s to haul juvenile fish from hatcheries to local lakes and since the 1950s to airlift and release them by the thousands into remote lakes everywhere.

But indiscriminate fish stocking is increasingly looking as if it might just be one of the dumber things people have ever done to the environment, because the introduced fish tend to displace native species. “Think about it,” says Julian D. Olden, a University of Washington ecologist working on nonnative fish issues. “The fish we stock are those that grow rapidly, are highly fecund and are great on the end of the hook,” he says, referring to the trout, bass, northern pike and other game fish that are commonly introduced to U.S. lakes and rivers. That is, we select for aggressive predators. “It shouldn't be too surprising that the same attributes we love as anglers are also responsible for the high impacts we are witnessing on native species and ecosystems,” Olden says.

Fish stocking has, of course, sometimes helped rebuild threatened native species—for instance, lake trout in the Great Lakes and brook trout in Great Smoky Mountains National Park. But until recently, hatcheries and fish stocking also made it easier to sacrifice rivers and lakes to development, observes Rick Williams, a fisheries biologist who advises Fly Fishers International. “[Development proponents] would say, ‘We're going to put this dam into this rivershed, and it's going to create all these benefits,’” he explains. The proponents would admit that there might be some negative effects on native salmon or steelhead trout, for example, but then they would gloss over those consequences, saying, “Don't worry, we're going to put in a hatchery.” Eventually, after the habitat was damaged beyond repair, people gradually realized that “hatchery fish are not wild fish.” The adaptations that let fish thrive in crowded hatchery conditions do not easily translate into survival or reproductive success in the wild. After just a single generation in captivity, hatchery steelhead already differed from their wild counterparts in the expression of hundreds of genes, according to a 2016 study.

State and federal officials, together with some anglers, have thus begun to rethink our long infatuation with fish stocking, and in some cases they are working to unwind its destructive effects. In August 2016 the National Park Service approved a plan to remove stocked fish from 85 high-elevation lakes in California's Sequoia and Kings Canyon National Parks. Also last year, Oregon removed limits on how many bass, walleye and other introduced game fish anglers can take in three rivers where those fish interfere with native species. In addition, a proposed nationwide network of native fish refuges moved toward becoming reality in 2015, when North Carolina, Georgia and Tennessee designated the Little Tennessee River basin the nation's first Native Fish Conservation Area.

Troubled waters

Concerns about the inadvertent effects of fish stocking have been around almost from the start. In Europe, people began to experiment with rearing fish fry in captivity to restock streams in the 17th century, and the practice spread to North America as waterways became fished out a century or so later. Olden likes to show his students an article from an 1893 Oregon newspaper arguing that introduction of largemouth bass would be either a blessing on the Columbia River (“the best friend not only of our salmon and trout, but of our water fowl”) or a curse (“the natural enemy of all young fish”).

But even those who should have known better seem not to have taken the potential hazards seriously. More than a century ago Robert Roosevelt, a New York State congressman who was an early conservationist (and uncle of Theodore), was largely responsible for instigating government stocking programs in the U.S. In 1871 he pushed Congress to establish the U.S. Fish Commission to investigate declining fisheries and the potential of aquaculture to replenish depleted waterways. Within a few years the new transcontinental railroad was shipping brook trout from east to west and rainbow trout from west to east, often stopping repeatedly en route to seed local bodies of water.

Commonly stocked species such as brook trout (1), lake trout (2) and northern pike (3) are aggressive predators. The fish are raised in hatcheries and then released into lakes and rivers (4), where they may displace native species. Credit: John Kuczala Getty Images (1); Getty Images (2 and 3); Stephen Osman Getty Images (4)

Enthusiasm for fish stocking blossomed from there, sometimes with devastating consequences. As early as 1910, the yellowfin cutthroat trout, a favorite of local anglers and known to weigh 11 pounds or more, disappeared from Colorado's Twin Lakes through hybridization with rainbow trout and competition with other introduced game fish. The same factors, together with overexploitation, killed off New Hampshire's silver trout, first described as a new species in 1885 and considered extinct by 1939. In one of the most egregious “improvements,” the state of Oregon deliberately poisoned the Miller Lake lamprey in the 1950s because it preyed on introduced trout. A 1989 study implicated the introduction of nonnative fish as a factor in more than two dozen North American fish extinctions over the previous century—and the rate of extinction appears to have increased by 25 percent since then.

“It's not only occurring in one place—it's all over the world,” says Vance T. Vredenburg, a herpetologist at San Francisco State University who has studied the effects of fish stocking on native species. “The California golden trout is a really beautiful fish, and because of that you can find them introduced in Mexico and in the Andes. You can find them in New Zealand. You can find them on Mount Kilimanjaro,” rarely with any consideration of the effect on native species. And yet invasive species and disease ranked among the top three culprits when the WWF reported in 2016 a stunning 81 percent decline in freshwater fish and amphibians worldwide since 1970.

In 2004 Vredenburg provided experimental evidence of the damage fish stocking does to mountain yellow-legged frogs, a species native to the Sierra Nevada. Working in Kings Canyon National Park, he began to suspect that brook trout and rainbow trout, introduced into high mountain lakes there that had never seen any fish before, were gobbling up all the native tadpoles before they could become frogs. To test his hypothesis, Vredenburg removed the introduced fish from five lakes in the park. Then, over a six-year period, he watched as the yellow-legged frog population rapidly recovered in those lakes, while tadpoles continued to vanish from eight nearby lakes that still contained introduced trout.

Other studies suggested that stocked fish were disturbing entire ecosystems in Kings Canyon National Park. Unexpected links tie one species to another, “and when fish are introduced, they sever those connections,” explains Danny Boiano, the park's aquatic ecologist. Yellow-legged frogs, for instance, were the main prey of mountain garter snakes in the park. When fish stocking made the frogs scarce, Boiano says, garter snake populations also declined. Gray-crowned rosy finches, birds that are partial to rocky alpine habitats, used to cruise the high mountain lakes to feed on mayflies. When introduced fish beat them to the mayflies, the finches became scarce. The fish also dramatically altered populations of Daphnia and other zooplankton that are the base of the food chain.

Vredenburg recalls that his initial study on yellow-legged frogs got no traction with policy makers at first, perhaps in part because the belief in the goodness of fish stocking is so strong. The U.S. Forest Service acknowledged that he had found a problem in that park, he notes, but it maintained that other habitats are different, saying, “We know places where frogs and fish coexist.” The experiment would have to be repeated to “show it was not just one place, not just one person's data,” Vredenburg says.

The California Department of Fish and Wildlife (then operating under the old name “California Department of Fish and Game”) also resisted any change to its fish-stocking practices. It was not so much a matter of economics as of “power, authority and mission,” says Kierán Suckling, executive director of the Center for Biological Diversity in Tucson, Ariz. Stocking fish was simply what fish and game departments, largely funded by fishing and hunting license fees, had always done. Suckling points out the contradiction: with one hand, the department was spending money to protect rare native fish, amphibians and other freshwater species, while the other hand was spending even more money stocking nonnative trout in waters where this practice was putting at least 39 such species at risk. But it took legal action from conservationists, together with the 2012 state (and 2014 federal) listing of the yellow-legged frog as an endangered species, to bring about change.

On the hook

California has since made major changes in its stocking practices, according to Roger Bloom, who manages inland fisheries for the California Department of Fish and Wildlife. For one thing, it has stopped stocking hundreds of lakes. And for those lakes it continues to stock, the state legislature has ordered a shift to stocking with native species, starting at a minimum of 25 percent of all stocked fish. In a few areas, the state now stocks only native species, notably Lahontan cutthroat trout in the Truckee and Carson rivers, where they are endemic.

“Our mantra,” Bloom says, “is to use the right fish in the right place at the right time and in the right numbers and to make sure we consider the benefits and effects at the ecosystem level.” The state now performs an environmental review of any new area proposed for stocking and periodic environmental impact statements on all stocked waters. Bloom says that when fishery officials in other states hear about this, their eyes widen in disbelief. “I think we're ahead of the others because of the complexity and the endangered species we've got,” he says.

Other states may have to catch up. “All states are supposed to look for sensitive species” before stocking, Suckling notes. “But they don't always do it unless you sue them.” A mix of what he describes as “weak and overly procedural” federal and state laws complicate the process. But in California, “the Endangered Species Act comes into play, and that's the big dog in the room,” Suckling says. “It's clear, it's strong, it's enforceable and that's when things tend to change more rapidly.”

Native species displaced by fish stocking can bounce back after the stocking of nonnative fish has stopped. Such remediation efforts may explain the recent recovery of the mountain yellow-legged frog in Yosemite National Park. Credit: Joel Sartore Getty Images 

It is also an outrage, to some anglers. When California announced a plan to protect native species by ending fish stocking in 175 lakes and streams, a headline on the outdoors column in the San Francisco Chronicle declared, “It's a Load of Bullfrogs!” “Every lake is somebody's favorite lake, so no matter which lake you stop stocking, it's going to make somebody angry,” observes Jessica Strickland, a fisheries biologist at Trout Unlimited, an organization of conservation-minded anglers based in Arlington, Va. “The local angler perspective is that they want to continue fishing where they want to fish. The conservation-minded angler who is more open to change says, ‘Maybe I can just go fish one of the other 9,000 lakes’” that continue to be stocked. For Trout Unlimited, she says, the important thing is for government agencies to operate in the open, giving anglers a chance to provide input and understand changes in stocking policy.

“At most, I would say we've only got significant conflicts [with endangered species] in 2 to 5 percent of stocked areas,” Suckling says of California's waterways. “And that's because the endangered species have retreated to small pristine areas. There's very little hope of bringing them back to the mainstream rivers. They're too full of exotic species and pollution.”

Elsewhere the move away from fish stocking goes slowly. Stocking with nonnative fish continues, for example, in the Little Tennessee River Native Fish Conservation Area, according to Fred Harris, an angler and retired fisheries biologist involved with the project. “Those rainbow and brown trout fisheries are very popular,” he says, “and the last thing you want to do, if you want to start a conservation process, is piss off a lot of anglers.”

Instead, he says, the project aims to work around the continued stocking. Removing river barriers is a priority, for instance, to open upstream areas to brook trout and other native species and to recover former habitat. At the same time, the project also maintains certain other barriers to keep the introduced rainbow and brown trout safely downstream.

That go-slow strategy may appease anglers, but it also poses risks of its own. The Little Tennessee River basin is an important site in one of the nation's great unheralded biodiversity stories: more than a third of the world's 840 freshwater mussel species live in North America, mostly in the Southeast. They have co-evolved with native fish species, developing ingenious adaptations to lure a fish close enough to blast their larvae into the fish's gills. The fish then becomes a traveling nursery for the mussel larvae and eventually disperses the young bivalves around the habitat. That dispersal maximizes the distribution of animals that spend most of their lives buried in the mud. It also benefits the habitat because the mussels filter bacteria and algae from the water.

But Suckling, whose Center for Biological Diversity has recently opened a Southeastern office, worries that continued stocking with nonnative game fish may displace native fish and throw the mussels' co-evolutionary strategies into the waste bin. Together with water pollution, dams, wetland destruction and other habitat changes, such displacement could push native freshwater mussels—already among America's most endangered species—into extinction.

Catch and release

The fight over fish stocking thus seems poised to become more widespread and perhaps uglier. But there is also promising news: in some areas where agencies have stopped stocking and actually removed introduced fish before it was too late, native habitats have bounced back. When researchers in the Italian Alps recently removed stocked brook trout from lakes in Gran Paradiso National Park, “recovery was very, very rapid,” says Rocco Tiberti of the University of Pavia. Daphnia and other native invertebrates that had been decimated suddenly blossomed. Dormant “resting eggs,” produced in periods of environmental stress years or even decades earlier, shed their protective envelopes and repopulated the lake. “Many populations can recover even after local extinction,” Tiberti observes.

Likewise, a study published in the Proceedings of the National Academy of Sciences USA in October 2016 announced a dramatic recovery of yellow-legged frogs in Yosemite National Park. Most news reports on the recovery emphasized the tantalizing possibility that long-term exposure to the deadly chytrid fungus, which has contributed to more than 100 amphibian extinctions since the 1970s, may have allowed the frogs there to evolve some form of resistance. But there was a hitch: yellow-legged frog recovery is so far happening only in Yosemite. A much simpler explanation, the authors of the study proposed, is that the frogs are recovering because in 1991 the National Park Service ended the practice of stocking high-elevation lakes with nonnative game fish. Although these lakes still harbor nonnative fish from earlier stocking efforts, discontinuation of that practice has given the frogs a reprieve, even in the absence of total elimination of those introduced species.

Back in the Sierra Nevada, watching his yellow-legged frogs leaving the threat of extinction behind, Vredenburg, a co-author of the new PNAS study, notes that humans have inflicted many ills on freshwater species, from pesticides to climate change. “It's death by a thousand cuts,” he remarks. “But amphibians have been around for 360 million years. They are survivors. If we can just remove some of these obstacles—such as introduced fish—we can give these species the opportunity to survive.”