Chemical isotopes trapped in the otolith, which forms layers like tree rings as it grows, tell the story of the salmon’s birthplace and life. Between 2 and 5 years ago, the sockeye hatched in this creek, a tiny corner of the sprawling network of freshwater lakes and streams along Alaska’s Bristol Bay. The fish headed out to sea and finally returned to its birthplace to spawn and die.

Over the past 2 decades, Schindler and colleagues have used otoliths and other data sources to illuminate how Bristol Bay consistently sees tens of millions of returning fish, year after year, making it one of the world’s most productive and lucrative salmon fisheries. The work has become a classic among ecologists, earning more than 1000 citations. Now, it has thrust Schindler into one of the biggest environmental battles of the early 21st century. A mining company wants to extract copper and gold from a massive ore deposit beneath headwaters of two of Bristol Bay’s main salmon rivers. The Pebble Mine could become one of the world’s biggest mineral producers, with an open pit nearly as deep as the Grand Canyon and vast infrastructure and waste piles that would stretch for kilometers.

Opponents of the project, including Native Alaskan, fishing, and environmental groups, have long argued that the mine’s short-term economic benefits would pale in comparison with the long-term risks to Bristol Bay’s salmon runs, including toxic runoff and habitat destruction. Critics have seized on Schindler’s science to help make their case, and in 2014 the findings helped persuade then-President Barack Obama’s administration to move to block the mine. But this year, President Donald Trump’s administration signaled it might allow the project as part of its efforts to encourage development.

The struggle has put Schindler at the center of the storm. The son of a scientist who also played a high-profile role in seminal environmental battles, Schindler inherited his father’s combativeness. The younger Schindler has collaborated with mine opponents and spoken out at public hearings. His views have gotten him kicked off a panel advising the mining company. And he hasn’t hesitated to criticize the Trump administration’s efforts to evaluate the Pebble Mine’s environmental impacts, calling a key study a joke. Doing so has made him a hero to antimine activists and a target for mine supporters, who say he has wandered far from his area of expertise.

At the heart of both his research and his advocacy lies this insight: Even in this land of superlatives, things as small as a tiny creek matter. The otolith he just extracted records one fish’s sojourn. He sticks it onto the back of his left glove for safekeeping, drops the remains into the water, and reaches for the next carcass. Ultimately, he and others will collect otoliths from some 8000 fish. “A lot of therapy,” he quips.

IN 1968, when Schindler was 4 months old, his crib was a wooden box used to ship a sonar echo sounder to a research station in remote western Ontario province in Canada. There, his father, limnologist Dave Schindler, was just starting an innovative project using 46 lakes as giant laboratories to study aquatic ecology.

The young Schindler came of age among the lakes, spending summers with scientists engaged in groundbreaking work. Over 2 decades, research at the Canadian government’s Experimental Lakes Area helped reveal how phosphorus pollution and acid rain damaged freshwater ecosystems. Dave Schindler’s work earned him the first Stockholm Water Prize in 1991, a sort of Nobel Prize for water researchers.

Before reaching his teens, Daniel Schindler knew how to handle a canoe and a motorboat. He and his two sisters spent summer days roaming the woods and handing sample-collection bottles to their father.

Daniel Schindler also saw how science can underpin activism. His father testified before various government bodies, facing off against the detergent industry about phosphates, and the electrical industry over coal-fired power plant emissions. In the early 2000s, Dave Schindler turned his attention to the environmental impacts of extracting oil from Canada’s tar sands. He once served as the scientific expert on a tour with rock star Neil Young, who was campaigning against tar sands extraction.

“Both of us would prefer to do our own things in some remote area and not be scrutinized,” says Dave Schindler, who lives in the Canadian Rockies near Radium Hot Springs. But, “You just feel, nobody’s speaking up; I’ve got to speak up.”

THIS PAST SUMMER, from the top of Church Mountain, Daniel Schindler could see the two arms of Lake Nerka reaching toward the horizon, framed by steep peaks. The only sign of humans were his field camp’s barebones cabins. Schindler has spent 23 summers here, much of that time chasing salmon through interconnected lakes gouged by glaciers. “I’m here because I love it,” he declares.

The landscape is vast. It’s also just a sliver of the habitat that produces Bristol Bay’s salmon runs. Nine large rivers drain watersheds covering an area the size of Virginia, virtually devoid of humans save for the occasional fishing lodge and native village. Over the past 4 decades, an average of nearly 40 million salmon have returned to the bay each year. (By comparison, it’s a good year when 3.5 million fish return to the Columbia River, the largest salmon river in the lower 48 states.) Most are sockeye, which spend their first year or two in freshwater and then head out to the North Pacific Ocean for 1 to 3 years before returning to reproduce. The deluge of fish draws more than 2000 commercial fishing boats, fueling a salmon economy worth about $300 million a year. Bristol Bay accounts for nearly half of all sockeye caught in the world.

For Schindler, this is one enormous laboratory. “I’m motivated to understand, how does this landscape work? What are the important features?”

Every year, he and his students track salmon returns by tallying dead and live fish in each 200-meter stretch of more than 30 streams. They net fish at creek mouths to see how many are scarred by nets. They track water temperatures, stream flows, nutrient levels, bear feeding, and myriad other clues to the intricate relationships between salmon and this place.

By now, he knows when the first salmon are likely to arrive in more than two dozen creeks. He can explain how nitrogen and carbon move through the streams, helping fuel the entire ecosystem. He can even tell you in which streams salmon carcasses have a bouquet of garlic, which of strong cheese, and which just stink of rotting fish.

Yet there’s always a surprise. In 2018, nearby Lake Beverley, which usually hosts modest spawning, unexpectedly filled with fish. The lake accounted for an estimated 13% of the global sockeye catch that year. That variability underlies one of the key insights by Schindler and colleagues: The resilience and productivity of Bristol Bay’s salmon population is due partly to a smorgasbord of habitats across a huge system.

Sockeye spawn everywhere, Schindler notes: in lakes, rivers, tiny spring-fed streams, and rocky creeks emerging from melting snowbanks. In a 2010 paper in Nature, he and co-authors used years of fish counts to show that even though annual fish numbers fluctuate dramatically in individual streams or river systems, the overall numbers in Bristol Bay hold remarkably steady. That’s because, most years, some waters somewhere are producing salmon even when others aren’t. The researchers dubbed that resilience the portfolio effect—a nod to the financial strategy of putting money into a variety of investments to guard against a downturn in a single one.

The otoliths add detail to the picture. As fish grow, the rings in those small “stones” trap chemicals from the surrounding environment—a signature that can vary from stream to stream. Schindler and others recently used the ratio of two strontium isotopes in sockeye and Chinook otoliths to figure out where the fish in one Bristol Bay river system originated. The results showed that the dominant source of salmon moved around the watershed from year to year, with some productive areas declining as others surged. Some streams might warm up in certain years, dampening salmon survival, Schindler explains. Low flows might keep salmon from reaching spawning grounds. Diseases, landslides, predators, a hard freeze, and ocean conditions can all take a toll.

This summer, the researchers here see that variation at play. A creek near the camp had once filled with 80,000 salmon. Then water levels in a spring-fed section fell, and this year fewer than 10,000 appear. A few kilometers down the lake, a swarm of salmon noses at the shoreline, trying to reach another creek. But they are out of luck: Winter storms have plugged the stream’s mouth with a wall of gravel.

Then there are places such as Allah Creek. This year, the stream fills with fish, even as it runs so shallow that salmon backs jut from the water as they sprint from the lake toward its first deep pool. The forest has come alive in response to the spawning. The air hums with carrion flies. Glaucous-winged gulls cluster on the beach, waiting for the next fresh carcass.

Schindler and his assistant, Eli Fournier, an undergraduate at Whitman College in Walla Walla, Washington, wade upstream, counting salmon. Pink eggs dot the streambed, like pearls from a broken necklace. Other fish—arctic grayling and Dolly Varden trout—gorge on the eggs. Signs of grizzly bears are everywhere. Bites mar salmon carcasses. The supply is so plentiful that bears often eat just the fat-filled brains and humps. “Bear kitchens,” where the grass is mashed flat and carpeted with fish bones, line the stream. The researchers punctuate their walks with loud calls of “Heyyyyy, bear!” to avoid surprising feasting bruins.

For bears and other animals that feed on fish, the variability from stream to stream is a boon. In one stream, spawning can start in early July, whereas in another it’s mid-August. That range expands the peak feeding season, when bears must store enough energy to survive the coming winter. Computer models suggest bears can forage as much as 75% longer when the timing of runs is more spread out, Schindler says.

The portfolio effect also benefits people, by sustaining salmon numbers in the bay. If all the streams varied in step, Schindler and colleagues calculated, overall salmon numbers would fluctuate so wildly that managers would need to close fishing every 2 to 3 years—10 times more often than they do now.

After nearly 3 hours splashing up Allah Creek, the final count is 3429 live and 1917 dead sockeye salmon. And one very live grizzly startled midmeal.

Can mining and salmon coexist?

IF NORTHERN DYNASTY MINERALS, based in Vancouver, Canada, has its way, a piece of the landscape will be transformed. Several versions of the Pebble Mine have emerged in company proposals and studies done by the Environmental Protection Agency (EPA) in Washington, D.C. Under the most expansive scenarios, it would become the world’s biggest gold producer and one of the top 10 copper mines, yielding up to 24 million tons of copper and 1400 tons of gold over its lifetime. An open pit covering 18 square kilometers would be the largest in North America. Infrastructure would include 125 kilometers of road and humanmade lakes full of toxic mine wastes covering an area nearly the size of New York City’s Manhattan island. It could employ more than 1000 people during regular operations and bring in revenues of $300 billion to $500 billion, according to an EPA study.

Even that massive operation would be dwarfed by the immense Alaskan landscape. Constructing a smaller version of the mine, for example, would touch on streams draining less than 1% of the land surrounding Bristol Bay, according to the U.S. Army Corps of Engineers.

But mine opponents fear that once roads and other infrastructure are built, the mine could expand and surrounding mining claims could become viable. And Schindler notes that even a single mine could have big impacts. It would straddle two of Bristol Bay’s watersheds. One drains into Lake Iliamna, Alaska’s biggest, which has produced about one-fifth of the bay’s sockeye salmon over the past 2 decades. The other feeds the Nushagak River, which has produced an average of 6.5% of sockeye populations.

“People have the general viewpoint that Alaska’s so big that there’s no way we could really screw it up,” Schindler says. But that, he says, is the same attitude people in the Pacific Northwest once voiced as rivers there were dammed and developed. Today, that region’s salmon runs have plummeted to a trickle, kept on life support at a cost of hundreds of millions of dollars.

In 2014, Obama’s EPA took the unusual step of announcing it planned to veto Northern Dynasty’s expected application for a federal permit needed to fill wetlands and streams, effectively killing the project. The agency pointed to a host of hazards: tens of kilometers of streams and tributaries destroyed, disruption of water flows, and the risk of stream pollution from copper—a potent aquatic poison—stirred up by mining. If a tailings dam failed in the earthquake-prone region, contaminated waste could pour down a nearby river. Even a smaller version of the mine, the agency declared, “jeopardizes the long-term health and sustainability of the Bristol Bay ecosystem.”

The portfolio effect underpinned those concerns. Though the mine would touch only a small percentage of the overall system, and even a catastrophic failure wouldn’t reach most watersheds, agency scientists feared that losing even some pieces could undermine the whole system. What would happen in years when salmon populations in other streams went bust, and damaged streams weren’t there to take up the slack?

Schindler’s work “was the most influential [research] in terms of how we approached Bristol Bay,” says Phil North, an aquatic ecologist who headed EPA’s Bristol Bay work before leaving the agency in 2013. In other words: Small things matter.

Trump’s election, however, as well as the later election of a pro-mining Alaskan governor, has given the Pebble Mine new life. In 2017, the company proposed a mine with a smaller footprint and more environmental safeguards, which it says would address EPA’s concerns. For example, the company says that after 2 decades of mining it would dump the tailings into the pit and cover them with water, eliminating the need for storage ponds.

Several federal agencies, now led by Trump appointees, have greeted the new plan more warmly. In February, the Army Corps, which controls federal wetlands permits, issued a draft environmental impact statement, finding the project would cause no population-level damage to salmon. In July, EPA withdrew its earlier veto proposal, saying its previous conclusion was outdated. Trump administration officials have suggested they hope to issue a final decision on the mine’s wetland permits by mid-2020. Whatever the timeline, any decision is certain to be challenged in court.

SCHINDLER BEARS AN UNCANNY resemblance to a grizzly. His head, topped by a thatch of gray-tinged brown hair, seems to rise straight from muscular shoulders. When he speaks, his heavy brow often furrows over close-set eyes in what resembles a glower, even when his voice has no trace of hostility.

He has turned that gaze on regulators and mine promoters, thrusting himself into the debate with characteristic bluntness. In April, he testified before a group of Alaskan state lawmakers about the draft environmental impact study, calling it a farce. “The Army Corps of Engineers should be ashamed of themselves and embarrassed if they are going to put this environmental impact statement forward as a piece of credible science. It is not.”

He scoffs at Northern Dynasty’s talk of a smaller, lower-impact mine. The company’s newest proposal calls for mining roughly 15% of the ore deposit and not reaching the richest veins. As a result, many critics, including Schindler, suspect the current plan is just a first phase, downsized to pass regulatory muster while opening the door to a much bigger future mine—with much greater environmental impacts.

Federal wildlife agencies have expressed similar concerns. The National Marine Fisheries Service and the Department of the Interior (DOI) have warned that the Army Corps has largely ignored the possibility of a bigger mine and understated or failed to consider risks to salmon. DOI officials wrote that the draft study was “so inadequate that it precludes meaningful analysis.”

The mine’s backers say a hypothetical bigger mine would have to win its own permit. “If there is a proposed expansion, that will have to go through the same permitting process,” says Tom Collier, a lawyer and CEO of the Pebble Partnership in Anchorage, Alaska, which is controlled by Northern Dynasty. Collier was second in command at DOI in the 1990s, during former President Bill Clinton’s administration.

Still, company officials have hinted that a bigger mine could follow. In November 2017, Northern Dynasty President Ron Thiessen told a mining industry conference that the initial mine would offer a chance to “get your social license and see where you go from that point.”

Mine backers also say concerns about salmon are exaggerated. The streams at the mine site are tiny, and in studies done for the mining company, researchers found no evidence that the waters could support significant salmon numbers, Collier says. That means they don’t really contribute to Schindler’s portfolio effect. “The bottom line is that where this mine is going in is not good salmon habitat, period,” Collier says.

Mine supporters have also questioned Schindler’s expertise and motivations, arguing he has acted as an antimine crusader rather than the impartial scientist he claims to be. In 2012, organizers of a Pebble-funded scientific review panel, the Colorado-based Keystone Policy Center, kicked Schindler out of the group after he co-wrote an editorial in the Seattle-based online magazine Crosscut, urging EPA to protect the region. Collier notes that Schindler isn’t an expert on mine-related issues such as design of tailings ponds and hasn’t studied the creeks that would be directly affected. Schindler is using his scientific credibility to “sit in a chair and express criticisms that are unrelated to his research,” Collier says.

Schindler’s defenders say he has stuck with the science and brings a deep knowledge of the whole ecosystem. “He’s the right guy, and he’s taken the bit in his mouth,” says Ray Hilborn, a University of Washington fisheries expert and director of the university’s Bristol Bay program.

Amid the crossfire, Schindler seems happiest waist-deep in a lake, counting sockeye. But he also appears to relish being part of the mine clash. He recently taught a university course dedicated to dissecting the Army Corps study. He has a fierce competitive streak, honed by ice hockey and sled dog racing as a child, and he says his father taught a key lesson: “Don’t be afraid to be bold.”

SCHINDLER ADMITS there’s still a lot to learn about Bristol Bay’s salmon. Scientists need “to keep poking away at this, trying to figure out what causes all these different dynamics,” he says. “We probably will never really figure it out.”

For him, that’s part of the point. If fisheries officials don’t know exactly what drives changes in salmon numbers or how to manage them, he says, it’s prudent to try to protect a variety of habitat and salmon runs, particularly in light of climate change.

To illustrate, one afternoon he drifts a small motorboat to a halt just offshore of Dead Moose Creek. It looks as promising as its name. Ankle deep and narrow enough to cross in four strides, the stream seems vanishingly insignificant. Scientists never even bothered to count fish there. “A stream like that, you say, ‘Well, that creek’s really nothing,’” Schindler says.

But this year is different. At the mouth of the stream, the water is alive with red backs and green fins. The fish are waiting, as their ancestors have for generations, for some unseen signal to launch themselves upstream.