Montana State University

Spring 2013





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Mountains and Minds

Char wars May 07, 2013 by Sepp Jannotta • Published 05/07/13

MSU scientists wade into fight against invasive lake trout in Montana's national parks

Six miles into Glacier National Park's backcountry, a skiff plies the water of Quartz Lake. A team of fishermen traces out nets in a careful pattern along the near-shore lake bottom. Working at night under peaks newly covered with snow, the fishermen set and pull their gear, some 2,000 feet worth of gillnetting, by hand.

This is no clandestine commercial fishing venture. The fishermen are, in fact, scientists, and their nightly exertions are a National Park Service fisheries management tool in motion--an ecological line in the sand.

Guided by Montana State University scientists and their surveys of Glacier's native and nonnative fish species and their habitats, gillnetting at Quartz Lake has become the cornerstone in a fight to save one native char--the bull trout--by knocking down an invasive char--the lake trout. MSU has been playing a very similar role in Yellowstone National Park's 17-year battle to suppress lake trout in Yellowstone Lake, where a once-thriving cutthroat trout population collapsed, largely because of predation from lake trout.

With gillnet panels sized to snare smaller juvenile and larger spawning-age fish, the goal of lake trout suppression is to pull in as many of the invaders as possible.

Catch enough lake trout and their population will crash, says Christopher Guy, a professor of fish ecology in the Department of Ecology at MSU. As the assistant leader of the Montana Cooperative Fishery Research Unit, a joint effort by MSU, the Montana Department of Fish, Wildlife and Parks and the U.S. Geological Survey, Guy's mission is to educate graduate students in fisheries science.

Hoping to answer questions about Glacier's fisheries, Guy has sent students into the park's wild westward drainages. These Flathead River tributaries are some of the last strongholds for the large-growing char known as the bull trout, found in both the Flathead and Hudson Bay drainages of the park.

Of particular interest was Quartz Lake, which biologists counted among the most ecologically intact watersheds in the Northern Rockies. That changed when lake trout were discovered in the drainage in 2005.

Now the war on Glacier National Park's lake trout has become a fight to preserve a handful of the most promising sites for bull trout.

There are 12 bull trout lakes that feed into the Flathead River system. MSU-led surveys determined that nine have been invaded by lake trout. At Quartz Lake, park officials decided to make their stand.

In 2007, a park-wide action plan was drawn up and in 2009 a decision was made to initiate an experimental lake trout suppression project on Quartz Lake. The project is unique because it is located in the park's backcountry, six miles from the nearest trailhead. Following a National Environmental Policy Act-required review of the plans, officials helicoptered a motorized skiff and materials into the lake and built a stone-reinforced fish barrier on Quartz Creek to keep out migrating lake trout.

In some of Glacier's marquee lakes, lake trout are well established and have local bull trout populations on the verge of blinking out. Officials decided some of them­--McDonald, Bowman and Kintla--would be left to fate for the time being.

"If we were to sit back and do nothing about lake trout, it's likely that bull trout would become functionally extinct in these lakes," says Clint Muhlfeld, an MSU-trained research ecologist with the USGS Northern Rocky Mountain Science Center in Bozeman and the University of Montana's Flathead Lake Biological Station. With help from Guy, Muhlfeld has been coordinating the gillnetting program at Quartz Lake.

Guy has dubbed the struggle: "The char wars."

A battle below the surface

Bull trout, once ubiquitous in the Columbia River system, are currently listed as threatened under the Endangered Species Act.

This species of char, native to the Pacific Northwest and Canada and close relative of the Dolly Varden trout is fond of cold, clear water. For spawning, bull trout typically require clean, stream-washed gravels, which Glacier's remote, snow-fed valleys offer to near perfection.

Also classified as char, lake trout thrive in the cold, still water of deep lakes. They stand out among the freshwater salmonids (both trout and char belong to the family salmonidae) because they feed voraciously on a mixture of invertebrates and smaller fish, much the same diet as bull trout.

Unfortunately for the native bull trout around Glacier, lake trout seem to play the part of top predator better, a role that may include predation on young bull trout.

Likewise in Yellowstone Lake, lake trout don't just out-compete the cutthroat--they eat cutthroat. Yellowstone National Park fisheries supervisor Todd Koel estimates that larger lake trout can devour between 40 and 50 cutthroat in a year.

"That kind of predation put the Yellowstone cutthroat into decline," Koel says.

In the late 1800s, lake trout came to the high-elevation lakes of the northern Rockies with a helping hand from the U.S. government, which hoped to bolster Western fisheries at a time when the region was still being settled.

The U.S. Commission on Fish and Fisheries began planting various cold-water species in lakes out West. In Yellowstone National Park, lake trout were introduced into Lewis and Shoshone lakes, in the headwaters of the Snake River drainage.

Federal fisheries managers also planted them in Flathead Lake.

Over the passing of a century or so, fish from Flathead Lake have migrated into many of the lakes upstream.

"We've discovered that lake trout are very opportunistic," Muhlfeld says. "They have a remarkable ability to move around and colonize new water if there aren't significant barriers in their way."

Char from afar in Yellowstone Lake

With a dozen miles of forest and the Continental Divide separating Lewis and Shoshone from Yellowstone Lake, exploratory urges cannot explain the arrival of lake trout in Yellowstone Lake in 1994.

MSU fish ecology professor Thomas McMahon, along with co-authors Andrew Munro and James Ruzycki, put to rest the notion that Yellowstone Lake always had an isolated ancestral lake trout population.

McMahon set out to see if chemical markers in fish otoliths, sometimes called ear stones, could be correlated to the mineral composition in a fish's water of origin. Since each body of water has its own chemical signature, they looked for a shift in the chemical markers laid down during otolith growth. Because otoliths show growth rings, much like a tree, the timing of a shift could be charted by age of the lake trout, which is one of the longest-living salmonids.

"We figured we'd take the oldest, largest fish in the system, and if they'd been introduced (to Yellowstone Lake), the chemical signal would show a difference that would correspond to that change," McMahon says. "And sure enough, in comparison to the younger ones, which had (a) flat line (graph), the older fish had this sharp rise in that signal."

The earlier signal was a match to Lewis Lake. The growth rings pointed to a transplanting in the late 1980s, likely around 1988. The culprit could have been birds of prey or some other wild animals that might have offered accidental lifts to lake trout or their fertilized eggs.

"In the end we pretty much know it was an animal--human beings--that planted the fish," says Robert Gresswell, MSU research professor and USGS research biologist with the Northern Rocky Mountain Science Center.

This kind of illegal transplanting is often called bucket biology. Park biologists called it potential disaster.

Action at Yellowstone Lake

Park officials quickly began assessing their options for protecting the Yellowstone Lake system cutthroat, a prized sport fish pursued by park visitors and an important food source for park wildlife.

Because Yellowstone cutthroat spawn in some 60 tributaries, they are also an important seasonal prey for grizzlies, river otters, bald eagles, osprey and other species. Lake trout, on the other hand, spawn on the lake bottom and are not readily available as a prey species.

In the decades since 1994, that population has dwindled alarmingly. The park's namesake lake, once the continent's most productive inland cutthroat fishery, now had spawning streams with few or no fish returning in the spring. Clear Creek, which as recently as the 1980s had supported as many as 50,000 spawning cutthroat, was down to 500 by the middle of the last decade. Predators turned elsewhere for food.

By 1995, park officials released "The Yellowstone Lake Crisis: Confronting a Lake Trout Invasion," an action plan on lake trout suppression that listed gillnetting and trapnetting as the most attractive options to suppress the population.

The strategy is written into the fishing history of the upper Midwest, where over harvesting and other factors devastated lake trout stocks. Once an important commercial fishery in the northern Great Lakes, lake trout are today reduced to a remnant population in only the largest of the lakes, Lake Superior.

Over the next 15 years, the Park Service spent millions of dollars working to catch lake trout. Biologists put radio telemetry tags on sterilized males, known as Judas fish, to map out the lake's primary spawning grounds. There, gillnets target spawners. A finer mesh net catches the juveniles.

But some fundamental questions loomed: Was the program working? Or were they simply removing some fish from a healthy, ever-growing population?

Research coming out of MSU helped answer the question.

A 2010 population study of lake trout in Yellowstone Lake led by John Syslo, an MSU doctoral student working with Guy, suggested that park efforts had not likely pushed lake trout toward the brink.

Over the past two summers, that research has guided the Park Service's ramped-up suppression effort at Yellowstone Lake. Park vessels were joined by the Hickey Brothers Fisheries Co., a commercial fishing contractor from Door County, Wis.

When fishing operations wrapped up last fall, the Park Service announced that more than 300,000 lake trout had been removed in 2012--a record catch. It also marked the first time the fishing effort had met the benchmark--a figure measured in the thousands of feet of gillnet deployed each day--suggested by Syslo and Guy's work.

"We are feeling good about the effort," Koel says. "The idea is to keep the number of catchable-size lake trout declining by more than half each year, which should effectively collapse the lake trout population."

Gresswell, who has led extensive efforts to use acoustic telemetry to track lake trout movements, points out the Park Service is seeing fewer fish hauled in per net.

"It's too early to tell if it's signaling the beginning of a downward spiral for lake trout, but that statistic is a big deal," Gresswell says. Biologists are also looking for a rebound in the numbers of Yellowstone cutthroat trout. Gresswell and Koel both say there is reason to be optimistic.

Park Service monitoring of cutthroat catches has shown two straight years of very strong production for small fish. Surveys of spawning streams have also shown cutthroat returning to streams that had recently been nearly devoid of spawning fish.

With more than a half million fish netted or trapped in the past two seasons--nearly as many as the previous 16 years combined--Park Service and MSU scientists say they hope the balance within the ecosystem is beginning to tip against the invader.

When they will pass that tipping point is an open question. According to Guy, population modeling will continue to help to define the fishing effort needed to reach that point.

"But it takes time and a lot of data to refine the models," Guy says. "This is ecology and the data are often messy."

Koel agrees.

"That's where the work coming out of MSU has been so important," Koel says. "It's giving us a better (target) to drive that lake trout population to its knees."

Targeting the Flathead system

Several hundred miles northwest of Yellowstone, in the upper Flathead drainage, state and federal biologists working on the lake trout problem also look to MSU science.

In the ancestral bull trout waters of Swan Lake, to Glacier's south, biologists with the Montana Department of Fish, Wildlife and Parks have declared another front in the war on lake trout.

In addition to helping with the gillnetting program there, MSU scientists are looking at other means of controlling the lake's invasive char. Donning scuba gear, Guy's MSU postdoctoral student Peter Brown and research assistant Nate Laulainen spent the fall diving in the lake's frigid water.

They were testing methods for delivering a lethal dose of electricity to the lake trout eggs that are deposited into lake bed gravel each spawning season. Similar electrofishing methods are being studied in Yellowstone. Despite challenges, Brown says he plans to return to Swan Lake in 2013.

For now, gillnetting remains biologists' most lethal weapon for suppressing lake trout.

As an October storm lashes Quartz Lake, Guy, Muhlfeld and Glacier National Park fisheries biologist Chris Downs take stock of their efforts.

Because the gillnetting program is relatively new at Quartz Lake and a lake trout population estimate is ongoing--it will be MSU student Carter Fredenberg's master's thesis--the biologists are cautiously optimistic about the falling catch rates they saw during the 2012 season.

"We certainly aren't going to say we've suppressed the population, but it is a good sign," Guy says.

But lake trout are only half of the equation.

Downs says they need to see stable or increasing numbers in their annual count of bull trout redds, or spawning beds, in upper Quartz Creek.

"That's one indication the lake trout suppression program is being effective," Downs says. "It's amazing to think of the effort and creativity that has gone into the Quartz Lake project thus far, from building a fish passage (lake trout) barrier in the backcountry using hand-tools, to flying a boat in here for gillnetting, to dedicated field crews spending long backcountry hitches netting at night in extreme weather."

Downs and Muhlfeld motor off into the gale heading across the lake to bushwhack along upper Quartz Creek in search of bull trout redds. What they find--big freshly hollowed out depressions in the streambed where bull trout deposit their eggs--is encouraging.

"The migratory bull trout population in Quartz appears to be holding steady," Muhlfeld says. "And we are working with Chris Guy and his MSU students on population models to measure our impact on Glacier's invasive lake trout. We turned to the best."

The battle to suppress invasive lake trout will be a "long haul," Guy says. The key for gillnetting programs, whether in Yellowstone, Swan or Quartz lakes, will be keeping suppression efforts up to a level that removes more fish than the ecosystems produce through spawning.

Because the struggle between native and invasive char happens underwater, out of sight of the public, Guy says it can be tricky to raise awareness about the ecological problems that result when lake trout take over.

"Hopefully MSU will be able to continue to provide the science to help the agencies working on this problem," Guy says. "Then, if it goes well, we can look back at this and say we left future generations a few special places where the ecological heritage is still relatively intact."

 

Mountains and Minds reporter Sepp Jannotta crosses Montana day and night to explore trout research at Montana State University.