Follow the fish

Fish-stocking has drawn otters to the Beartooth Plateau of Montana. What effect do they have in their new environs?

On a moody September afternoon, Patrick Cross stood on top of a rock and inspected the banks of a creek that flowed steadily out of Beauty Lake, an alpine lake in the Beartooth Plateau, a vast stretch of high plateau on the border of Wyoming and Montana.

Cross, an ecologist at the Yellowstone Ecological Research Center in Bozeman, Montana, was looking for river otters. Nearly six years ago, he found some otter scat near here, a sign that the animals use to mark their territory. Otter scat is black and streaky, and it should be easy to see against the pale gray granite rocks. And otters typically prefer large flat surfaces onto which they can haul their entire bodies when they do their business.


“If I were an otter, I’d be pooping all over that thing,” Cross told me, pointing to a big flat rock a few steps away. He stepped confidently on the stony nubbins of granite that ringed the lake, never tripping, to reach the rock of his interest. His dog, Pika, an 11-year-old Montana cowdog, followed loyally. Cross knelt to get a closer look; sometimes, scat disaggregates and turns into a pile of translucent fish scales. But much to his disappointment, the rock was bare.

Otters were once unheard of in the Beartooths. In fact, there’s no evidence they’re native to this high alpine environment at all; their arrival appears to be part of the sweeping changes humans have brought to the plateau. In the 1960s, zoologists Donald Pattie and Nicolaas Verbeek spent years surveying the various mammals found in the Beartooths. They found creatures as small as dwarf shrews and as large as grizzly bears and mountain goats, but no otters. Continued but sporadic surveys done by field technicians and researchers at the Yellowstone Ecological Research Center in the 1990s yielded no sign of river otters, either. But for the last decade or so, there have been a few anecdotal reports from Cross, his colleagues, and some of the locals who frequent the plateau.

No one seems to know when the otters started showing up or what led them to migrate to this rugged landscape in the first place. So Cross is on the case, not just trying to find some otters but hoping to figure out how they got here, and what exactly they might be doing today.

Growing up in Billings, Cross spent most of his days outside, with the Beartooths as his backyard. Both of his parents skied, and when he was 5, Cross’ mother started taking him out of kindergarten early so that he could learn to ski, too. Soon after, he joined the Boy Scouts, and his troop frequently made outings to the Beartooths. His group once built a raft entirely out of logs and took it down the Stillwater River, which flows out of the Beartooths. In high school, Cross and his close friends would backpack or ski into the mountains in search of new peaks to climb, lakes to fish and lines to ski. His parents gave Cross the freedom to explore, even if at times they were wary of some of his excursions.

After Cross graduated from college, he worked on a fishing boat in Alaska for a few months, and then as a biological science technician in Yellowstone National Park. In 2012, after a few field seasons tracking bears and wolves, he began a master’s in systems ecology at the University of Montana and the Yellowstone Ecological Research Center, tracking foxes in the Beartooths. He spent two winters living out of an RV on Beartooth Lake, tucked at the foot of Beartooth Butte, an orange and clay-colored monolith made of limestone and shale. In the winter, the lakes iced over and were covered in a thick blanket of snow, and he spent his days on skis, following fox prints to see where the animals were going.

On a dreary day in January 2013, Cross and his colleague were scouting for fox tracks when they found a pair of tracks that they couldn’t place. Each print had five toes and measured about 3 inches wide. At first, Cross wondered if these tracks belonged to a fisher, a small, weasel-sized animal that’s rare in the Beartooths. But when he followed them, they descended into a hole in the ice. That set off an alarm: Fishers don’t swim. “That’s when I had an inkling that maybe these could be otters,” Cross said.

On subsequent trips, Cross started looking for otters. About four months later, he was tracking red foxes around Beartooth Lake in the brutal cold, when an otter suddenly shot out from under him. It bounded ahead and then slid on its belly, over and over, until it found a hole in the ice. “He took one look at me and then slid into the water,” Cross said.

Patrick Cross, an ecologist at the Yellowstone Ecological Research Center, wants to understand why river otters are moving into the Beartooth Plateau.
Wudan Yan

HISTORICALLY, NOT ONLY DID THE PLATEAU LACK OTTERS, it was devoid of the fish they prey on. In fact, before the West was colonized, the majority of mountain lakes in the area lacked fish. Physical barriers, like waterfalls, prevented fish from moving upstream into high alpine lakes, and the lakes were typically covered with ice 10 months a year, making them unsuitable for most fish. When Europeans — cattlemen, miners and sportsmen — colonized the American West in the 1800s, they started introducing trout into the high lakes wherever they could.

Fish stocking continued into the 1900s, when state fish and wildlife organizations took over, building hatcheries to spawn fish to populate the West’s lakes. Fish stocking, according to former aquatic biologist Edwin “Phil” Pister, had “the singular goal of creating and enhancing sport fishing and without any consideration of its ecological ramifications.” Even today, stocking is funded by the Dingell-Johnson Act of 1950, which taxes angling permits and equipment.

Any new addition to an ecosystem is going to have consequences. In Northern California, stocking of trout in alpine lakes threatened the frogs and salamanders native to the lakes. Researchers started documenting the loss of invertebrates and bugs — essential prey for bats, birds and snakes — following fish stocking as early as the 1950s, and ecologists continue to publish similar findings.

Raising fish in hatcheries and then stocking them in mountain lakes is a remarkably unnatural process. In a hatchery, the fish are raised until they’re about 3 to 4 months old and about 2 inches long. At that time, these so-called “fingerlings” get transported via helicopters to wilderness regions. The helicopters then hover over the lakes and drop the fish into their new home, creating a piscine waterfall.

In the 1970s, the management of fish stocking changed in the Beartooths. State fish and wildlife technicians treated the lakes with rotenone, a chemical that could kill all fish in a given body of water. Once those fish perished, wildlife managers restocked the lakes with Yellowstone cutthroat trout, which are indigenous to the greater Yellowstone ecosystem. They reasoned that the lakes in the Beartooths, which are part of that ecosystem, could be stocked with the same fish.

Moreover, Yellowstone cutthroat trout — a dietary staple for grizzlies, ospreys, eagles and river otters — are in decline, due to competition and predation by non-native fish. The Beartooths’ lakes provide a genetic refugia for the species. “If a volcano took out the Yellowstone River and got rid of the Yellowstone cutthroat trout, we’d still have a lot of Yellowstone cutthroat trout in the mountains,” said Chris Phillips of Montana Fish, Wildlife and Parks.

Today, the only stocked lakes in the Beartooths were grandfathered in before the Absaroka-Beartooth Range was designated as wilderness in 1978. New batches of fish are dropped off every two to eight years, depending on how many anglers visit a particular lake, how large the lake is, and how well the fish do once they’re stocked. But most of the high alpine lakes of the Beartooths have few nutrients and as such, offer poor habitats for these newly stocked fish. After eight years or less, the cutthroat are usually on their last tail.

Fishing is a huge draw for backpackers in the region. Many small towns on the way to the Beartooths have a storefront or two designed for outfitters or anglers, and it’s rare to find a backpacker or dayhiker in the plateau without a fishing rod. Even Cross keeps one in the back of his car.

Now, those stocked fish in the Beartooths may have drawn a new predator to the plateau: the otters Cross spotted. The playful and elusive mammals had their own trouble with stocking in nearby ecosystems. North American river otters are not currently at risk of extinction. But in Yellowstone National Park, illegally stocked lake trout in Yellowstone Lake precipitated a huge decline in the native cutthroat trout population, as well as in the otters that feed on those fish. The Beartooths lie just northeast of Yellowstone Lake.

A river otter in Soda Butte Creek, Yellowstone National Park, February 2009.
Patrick Cross/ Yellowstone Ecological Research Center

Merav Ben-David, a wildlife biologist at the University of Wyoming who studied the effects of lake trout stocking on river otters in Yellowstone Lake, says it’s possible that the open space and the amply stocked lakes of the Beartooths provided enough food and room to satisfy the river otters pushed out of Yellowstone Lake. But no one will know for sure where these otters came from, unless their genes can be compared to those of river otters in adjacent ecosystems — a question that Cross hopes to explore in the future.

Meanwhile, the impact the otters might have on the ecosystem of the Beartooths is unclear. Without large predators that prey on otters, there are no animals to keep the population in check. “Because there’s so much fish, the opportunities for the otters are pretty much unlimited at this point,” Cross said.

But it might not be a bad sign if otters are in the Beartooths. Like their prey, they are bound to be negatively affected by climate change and environmental pressures. “If we can create new habitats for them at higher elevations, all the better,” says Ben-David.

Source: Yellowstone Ecological Research Center; Map: Luna Anna Archey/High Country News

STUDYING OTTERS IN THE WILD, as Cross aims to do, isn’t easy. They tend to be nocturnal, territorial and dispersed. They’re also difficult to trap live. “It would be an ongoing, very labor-intensive, and sometimes not very productive effort,” says Thomas Serfass, a wildlife biologist and otter specialist at Frostburgh State University in Maryland. The best way to learn about the presence — or absence — of otters, he says, is by identifying their latrines and then watching how the animals move from those particular areas.

For Cross, latrine sites are an important indication of possible changes in otter behavior in the Beartooths. But he found he needed more help, beyond the sparse anecdotal reports of his friends and his own rare sightings. He thought that a project dealing with a “charismatic carnivore” like the otter would provide an opportunity to get ordinary citizens involved. “If we can use a charismatic animal like the otter to engage people — to get people to value conserving that species and its habitat — it will benefit the other species that use that habitat, too,” Cross said.

In November 2017, Cross launched a project on, a site where scientists and researchers can crowdfund various projects. In less than two months, he raised more than $3,000 to help pay his “citizen scientists” to join him on a cross-country ski expedition to track otters.

Cross identified six transects and corridors where otters had been spotted and might be seen again. Last Memorial Day weekend, 17 people showed up to look for tracks along those transects to see how far into the plateau the otters had traveled to, to collect scat to analyze their diet, and to see whether there were families of the animals around.

It was still wintry on the day of the expedition, fortunately: Looking for otters in the winter is much easier, since tracks and scat are more obvious against the snow. In the summer, animal tracks may be everywhere, but they’re much more difficult to discern.

Rusty Willis, a local climber, was one of Cross’ helpers. Willis had grown up in the Beartooths, though he’d never seen otters up here But once he learned about Cross’ project through a friend, he started noticing otter tracks everywhere. “It’s not like you could mistake it for something else,” he said.

Towards the end of the day, as Willis skied near a stream, he saw an otter poke its head out of the water. There were no tracks leading to its location, and Willis fumbled to get his phone out. But he was too slow. The otter swam downriver and re-emerged in front of Willis’ ski partner, ran across the snowy bank and dived back into the river. Willis and his partner measured the tracks in the snow. Cross and the other volunteers, skiing along separate transects, saw tracks, but no other live otters. Some volunteers collected scat samples for analysis, but they were all infested with tapeworms and therefore useless.

Nick Hackman, a volunteer with the Alpine Otters Project, investigates a set of adult river otter tracks crossing an ice floe on Kersey Lake in the Beartooth Mountains, Montana, during a citizen science field day last May 20.
Patrick Cross/ Yellowstone Ecological Research Center

ON THE HIKE OUT FROM BEAUTY LAKE, Cross moved quickly, almost speed-walking. The weather — as unpredictable as it can be in the alpine — quickly turned from sunshine to a light drizzle, and storm clouds started to roll in. Shortly after, along the trail, we ran into two backpackers — Don Sharp, his brother-in-law, Robert Kietler, and his dog, Pepe.

“See any otters?” Cross asked, as he asked almost everybody we met on the trail. Most people have said no, surprised it was a possibility.

“Actually, yes!” exclaimed Sharp. At that moment, Mother Nature joined the conversation, throwing sleet and hail at us, and we took cover under a whitebark pine. Sharp dug into his backpack for his camera and showed us a photo of three otters up at Crystal Lake, a little over 6 miles northwest of Beauty Lake. Sharp said he’d spotted them swimming and bobbing their heads out of the water. One of the otters looked much younger than the others, a sign that they could have been a family.

This was a repeat trip for Sharp and Kietler, they said. On a trip to Crystal Lake a few years ago, they caught plenty of fish. This time, they came up empty. “We thought the lake was barren, and then we saw the otters,” said Sharp. “Now we know why.” (It’s possible for otters to completely consume all the fish stocked in an entire lake, said Ben-David.)

Patrick Cross, an ecologist at the Yellowstone Ecological Research Center, examines otter scat found at Beartooth Lake, Wyoming, finding it full of fish bones.
Wudan Yan

When the hail subsided, we wished Sharp and Kietler luck on the rest of their backpacking trip, got back in the car, and headed towards Beartooth Lake in search of more otter signs.

We parked Cross’ Ford Ranger at the trailhead and walked toward the inlet of the lake. I made my way clumsily around the rocks, trying not to dunk my feet in the water. Cross sprinted ahead and called me over to a small grass patch. While the other grasses in that area reached my waist, this section was flattened. Two black, greasy streaks sat at the center: otter scat. Cross picked up some twigs and used them to pick apart the scat.

“It’s like Christmas or something,” he said. “You just start unwrapping the present and you never know what you’re going to find or uncover.” In some fox and marten droppings, for instance, he’d found balls of hair, or minuscule portions of another animal’s claws.

As Cross picked apart the flaky scat, prickly fish bones emerged, along with tiny fish scales, a fish eye, and the larvae of a caddisfly. It fit the idea that the otters were mostly drawn to the fish in their new homes, and suggested that they weren’t eating much beyond the fish humans have put here. The scat was fresh and greasy, indicating that the otter had been there recently, perhaps within the last day or so.

To the left of the scat, Cross pointed out the slide that the otter made to get back in the water after it left its droppings. We walked slowly along the banks and watched the water closely, looking for anything breaking the surface. The mud squelched beneath our shoes. Fish ripples dotted the surface, but no otters came up for air. After a few minutes, we headed out, leaving the lake and its inhabitants in peace. 

River otters traverse the icy Yellowstone River between Hayden Valley and Canyon, Wyoming, where they swim in unfrozen holes and race from one to the next.
Michael L. Haring via Istock

Wudan Yan is an independent journalist who writes about science, health, the environment, human rights and international issues. Although frequently itinerant, she is based in Seattle.

This story was funded with reader donations to the High Country News Research Fund. Email High Country News at [email protected] or submit a letter to the editor.



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