Yellowstone lake trout mystery: The work of an environmental vandal or did the fish swim there?

(National Park Service)

JACKSON, Wyo. — 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 themselves.

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 told the Jackson Hole News & Guide.

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 all the way over the top,” Koel said.

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.

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, which is a keystone of the Yellowstone Lake food web by 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.

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 by doing another otolith study.

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.

Varley, formerly Koel’s boss, is 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.”

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