A new culprit is under suspicion in the unsolved case of who “stocked” Yellowstone Lake with nonnative trout, an ecological disaster now costing the government millions of dollars to control.
The conventional theory explaining the unwelcome newcomer, backed by some hard data, has been that a “bucket biologist” scooped lake trout out of nearby Lewis Lake and dumped them into Yellowstone Lake.
Suspecting foul play, officials offered a $10,000 reward in the mid-1990s for information leading to the arrest and conviction in the crime once dubbed “an appalling act of environmental vandalism” by former Yellowstone National Park Superintendent Bob Barbee. An emerging theory suggests the vandals might be the fish.
Yellowstone’s chief fisheries biologist, Todd Koel started investigating a case of trespass not transport after seeing how fish are invading high-elevation lakes in Glacier National Park.
Koel emphasized that he’s merely suggesting an alternative hypothesis to explain the 1994 appearance of lake trout in the prized 136-square-mile lake, and one that needs more testing to prove. But it’s a line of thinking he’s taking seriously enough that he’s in the peer-review stages of completing an academic paper.
Koel suspects that some of the scores of lake trout that wash out of Jackson Lake Dam in Grand Teton National Park swam up Pacific Creek, the first major drainage downstream of the dam’s spillway. After a 40-mile swim, fish would arrive at North Two Ocean Creek, the stream that gives birth to Atlantic and Pacific creeks at the hydrological oddity known as the “Parting of the Waters.” Pacific Creek drains into the Snake River, while Atlantic Creek empties into the Yellowstone River.
“There’s surface water that connects up Two Ocean Pass, the waters of the Pacific drainage and the Atlantic drainage,” Koel said.
Fish making the hypothetical 80-mile lake-to-lake trek would encounter no true barriers to movement and would be dispersing up and down relatively low-gradient streams, he said.
“I flew it last year and it was an open system from Jackson Lake,” Koel said, “all the way over the top.”
The Pacific Creek-Atlantic Creek passage over the Continental Divide is the same presumed route that cutthroat trout traveled thousands of years ago, when they first inhabited Yellowstone Lake and the larger Missouri River basin after the last period of glaciation.
If lake trout have indeed dispersed from Jackson into Yellowstone lake, it’s unlikely they’re making the trip every year, Koel said. The species has occupied Jackson Lake for over a century, an extended time that makes the possibility more plausible, especially during high water years when Two Ocean Pass becomes so flooded the fish could swim across as if they were in a lake, he said.
‘Environmental vandalism’ doubted?
An ongoing invasion of lake trout into high-elevation lakes in Glacier National Park sparked Koel’s theory. The fish actively taking over a dozen lakes on Glacier’s west side got there by conquering high-gradient streams strewn with boulders and cascades. If lake trout can do that, Koel figured they could manage Two Ocean Pass.
U.S. Geological Survey aquatic research ecologist Clint Muhlfeld affirmed that lake trout tagged with tracking equipment in the Flathead Lake watershed have made grand journeys. Lake trout have their name for a reason and cannot persist long term in flowing water, but they’re plenty capable of surviving extended forays into the habitat of their fluvial cousins, he said.
“We found that these lake trout exhibited long-distance movements upstream, some way up into Canada almost 150 kilometers from the place where they were tagged,” Muhlfeld said. “It was really the first study to show how lake trout can exhibit long-distance dispersal movements. That kind of reassured us that they can pretty much get anywhere, given the right situation.”
Lake trout’s invasions into the headwater lakes of the Flathead drainage have rendered native, endangered bull trout “functionally extinct” in 11 of the 12 Glacier Park lakes where the two species are now sharing habitat, he said.
In Yellowstone Lake, cutthroat are the native species falling victim to lake trout. Also called mackinaw, lake trout are a predominantly fish-eating species naturally found in the Great Lakes, much of Canada and along the Eastern Seaboard.
The larger, deepwater-dwelling trout is considered the primary culprit in the collapse of the native cutthroat population, a keystone of the Yellowstone Lake food web, feeding water shrews, ospreys, grizzly bears and dozens of other species during their springtime spawning runs. The native trout are also valuable to humans. Yellowstone officials estimated the annual economic value of the cutthroat sport fishery at $36 million annually when lake trout were first discovered 24 years ago.
Cutthroat numbers are now thought to be on the rise, thanks partly to a $2 million a year gill-net-fishing program designed to crash the lake trout population.
After their 1994 discovery, debate brewed for years about when and how lake trout got into Yellowstone Lake.
One theory was that water-hauling aircraft unknowingly scooped the fish out of Lewis and Shoshone lakes while firefighting the 1988 wildfires and dropped them onto flames that burned near Yellowstone Lake tributaries.
Other fishermen have contended that they’ve been in Yellowstone Lake for more than a century. A citation in Hiram Martin Chittenden’s 1904 book “Yellowstone National Park” reported planting “10,000 yearling lake trout in the Yellowstone River above the falls in 1890.” Modern Yellowstone officials have said that is an error, pointing to there being no photographic evidence of a lake trout being caught for another 104 years.
Another theory holds that lake trout escaped from display tanks they were kept in at the old Yellowstone Lake Hatchery during the 1940s and ’50s.
It was a 2005 study headed by former Montana State University researcher Andrew Munro that, for a while, seemed to close the case.
“That sort of iced it for us, at that time,” retired Yellowstone science chief John Varley said.
Munro examined small stones called “otoliths” that grew in the ears of Yellowstone Lake’s mackinaw captured between 1996 and 1999. The otoliths are telling of the water chemistry of the bodies of water that fish occupied during each year of life.
“The dating of the abrupt shifts in otolith chemistry as occurring in 1989 and 1996 suggests that multiple transfers may have occurred,” Munro wrote in the 1995 study.
Lewis Lake, he found, is the “likely source of the transplanted lake trout.”
Jackson Lake, which originally got its lake trout from dispersing Lewis Lake fish, was not included in the study.
“They really only looked at Lewis Lake,” Koel said. “Sure enough, the genetic study that was done showed that yes, some of the lake trout in Yellowstone Lake came from Lewis Lake. But even in that report, it says that some of the fish genetically look like they came from another source, maybe a source connected to Lewis Lake. They threw out Jenny Lake as an example of a place where they maybe could have come from.”
USGS’s Muhlfeld, who’s experienced in otolith chemistry work, said Koel’s theory could be proven or debunked in a laboratory.
“The way to test Todd’s theory,” Muhlfeld said, “would be to actually redo the otolith study to get some samples from Jackson Lake and compare it to Lewis Lake to see where some of those early sampled fish in Yellowstone best matched.
“You could do it,” he said.
Snake River dispersals
Wyoming wildlife managers, who manage Jackson Lake as a trophy lake trout fishery and stocked them until a decade ago, do encounter errant mackinaw during routine sampling of the Snake River watershed below the dam. The Snake immediately past the spillway is a popular springtime fishing hole, and the primary quarry is lake trout.
“I wouldn’t say it’s annual, but it’s not that uncommon to find a lake trout or two,” said Rob Gipson, fisheries supervisor for the Wyoming Game and Fish Department’s Jackson Region.
Last summer, for example, electrofishing crews nabbed an 18-inch lake trout out of the Gros Ventre River. There have been other unexpected catches: mackinaw sampled in the Snake, Hoback and Salt rivers, and even in Flat Creek.
Gipson’s take on Koel’s theory is that it’s interesting, but he’s not yet convinced of its merits.
“Lake trout don’t really like that,” Gipson said. “It’d be a long journey.
“I don’t ever remember seeing a lake trout in something smaller than Flat Creek,” he said. “We do shock a lot of small tributaries in wilderness and higher up in the drainage and have never seen a lake trout. That, to me, says if it were to happen it would be extremely rare.”
Koel knows that there’s still work to do to confirm his hunch. It will take time and money to research the theory further, and it might not be a priority for resources because the mechanism by which lake trout got to Yellowstone Lake won’t change management. Lake trout will continue to be netted and killed either way, he said, in the fight to help cutthroat stage a comeback.
Still, the unlikely upstream invasions in Glacier have him wondering if the same thing happened in northwest Wyoming.
“Who would have thought a lake trout is going to go up a mountain stream, right?” Koel said. “But work that Clint [Muhlfeld]’s done since has demonstrated that ability. That’s why I’m suggesting this alternative hypothesis.”
Count Varley, formerly Koel’s boss, among the skeptics who are intrigued but not convinced. He pointed out that since the glaciers receded from the Yellowstone Plateau over 10,000 years ago just two species of fish have occupied Yellowstone Lake via the Parting of the Waters: cutthroat trout and the long-nosed dace, a minnow species. Downstream of the lake there’s an obvious barrier blocking movements: Yellowstone Falls’ two cascades.
“Coming over Two Ocean Pass is a 1-in-5,000-year event based on those two successful passages,” Varley said. “I still favor the evil-deed theory. That’s basically from discussions with longtime park employees.
“That’s easily done, either in early June or September,” he said. “They’re catchable along the shoreline [of Lewis Lake], and even the shoreline next to the road. All you need is an Igloo cooler, and boom.”