Montana State University

Spring 2009

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Mountains and Minds

Has whirling disease come full circle? April 27, 2009 by Evelyn Boswell • Published 04/27/09

MSU scientists ask why rainbow trout populations are on the rise in rivers once nearly decimated by the disease

Dick Vincent works with wife Jennie Miles of Pony, who maintains the lab. Photo by Kelly Gorham.
Dick Vincent works with Jennie Miles of Pony, who maintains the lab. Photo by Kelly Gorham.

Living the dream of an uber-angler, Dick Vincent once spent 10 hours a day, six days a week, fishing the streams of northwest Montana.

A Montana State University student in the 1960s, he cast his line-over and over for two summers-until he caught and tagged 4,500 cutthroat trout for researchers at the Montana Department of Fish, Wildlife and Parks. The process left him temporarily fish fatigued, but it led to a 42-year fisheries career that placed him at the forefront when whirling disease threatened to destroy the state's rainbow trout population.

Vincent, 68, retired this year after 12 years as whirling disease coordinator for the FWP, eight years as fish manager for Region Three of the FWP and 22 years as area biologist over the Madison, Gallatin and upper Missouri rivers.

Now focusing on miniature dachshunds instead of juvenile trout, Vincent left behind longtime collaborators at MSU and elsewhere who continue to search for solutions to whirling disease and other parasitic diseases.

Whirling disease infects about 150 streams across Montana, but Vincent said he is optimistic about the future of trout fishing in Montana. One of the most promising developments is the discovery of wild rainbow trout that are naturally resistant to whirling disease. Another is the mysterious rebound of rainbow trout in the first Montana river where whirling disease was discovered.

Into the wild

An MSU graduate who received his bachelor's and master's degrees in fish and wildlife management, Vincent started noticing in about 1991 that young rainbow trout populations were showing large declines in the upper Madison River. He didn't know why. As time went on, rainbow trout--especially young rainbows--continued to decline, so he met with top FWP officials to figure out how to tell the public that their blue ribbon trout stream was in serious trouble. By 1994, the rainbow trout population in the upper Madison had fallen by 90 percent.

Researchers studied whirling disease from every angle. The goal was to understand how whirling disease worked, the eradicate it.
"When I first heard of whirling disease, I didn't pay much attention to it," Vincent said. "I thought, 'OK, it's probably a hatchery disease and not really in the wild.'"

Testing proved him wrong.

A scientist friend was convinced that whirling disease was responsible for the rainbow trout crash in Colorado and suggested that the same could be true for Montana. As a result, Vincent sent some of the Madison River trout to a histology laboratory at Washington State University. The lab determined that whirling disease was, indeed, responsible for Montana's situation and set the course for the state's response.

FWP officials appointed Vincent their whirling disease coordinator in 1996. About the same time, Congress approved the Whirling Disease Initiative to find practical ways to maintain viable wild trout populations despite whirling disease. The initiative originated with a consortium called the National Partnership on Management of Wild and Native Cold Water Fisheries, administered by the Montana Water Center at MSU and provided funding for a variety of projects across the West.

Researchers whose projects were approved studied whirling disease from every angle they could imagine. Some investigated the two-host life cycle in fish and the aquatic worm Tubifex tubifex. Others analyzed the roles of water temperature, water quality and river sediment. The original goal was to understand how whirling disease worked, then eradicate it.

Whirling disease occurs when a microscopic parasite called Myxobolus cerebralis latches onto the skin of young fish, usually rainbow trout. The parasite then works its way into the fish and injects a series of infective spores into the muscle tissue, where the spores migrate to cartilage, the parasite's food source, Vincent said. The damaged cartilage causes severe deformities in the fish. When the fish's body tries to attack the parasite, it causes inflammation and infection within the fish. If most of the infection is on one side of the fish's body and causes nerve damage, the fish's brain can only communicate with one side of the body. Instead of swimming forward, the fish starts to whirl.

"Not a good thing to do when you are trying to escape a predator or eat," Vincent said.

Every infected fish doesn't whirl, but whirling disease got its name from those that did, Vincent said.

In the process of dying or being eaten, rainbow trout release Myxobolus spores into the water, Vincent said. Tubifex tubifex worms then eat the spores, which can survive in river bottom sediment or dry mud for up to 30 years. Within three to four months of settling in the worm's gut, the spore opens and a new infective version of the parasite emerges. It's called a Triactinomyxon or TAM. When the worms excrete TAMs into the water, the free-swimming TAMs start latching onto fish again. The cycle continues.

Spores like it cold

These rainbow trout have deformed tails and other clinical signs of whirling disease. Not all fish have the same symptoms. Photo courtesy of Stephen Atkinson, Oregon State University.
These rainbow trout have deformed tails and other clinical signs of whirling disease. Not all fish have the same symptoms. Photo courtesy of Stephen Atkinson, Oregon State University.

After receiving confirmation that whirling disease had moved into the Madison, Vincent said it was hard to know what to say in his Whirling Disease Initiative role. He never claimed to be a psychic, but the media wanted him to predict the future of trout fishing in Montana. As a result, he and other scientists guessed that whirling disease would be far more devastating than it turned out to be.

"Almost nothing was known about whirling disease in the wild prior to 1994 for Montana and 1993 for Colorado," Vincent said.

By 2006 or 2007, researchers had an amazing grasp of whirling disease in Montana
By 2006 or 2007, with dozens of research projects behind them, the researchers had an amazing grasp of whirling disease in Montana, Vincent said. They knew, for example, that young fish were especially susceptible to whirling disease, because at that point in their development their skeleton is mostly made up of cartilage instead of bone. The effect of their deaths ripples through the population, until observers finally notice a dearth of adults.

Scientists learned, too, that whirling disease flourishes when water ranges between 40 and 68 degrees F, Vincent said. When the temperature reaches the mid-70s F, the worms actually expunge the spores from their bodies. High water temperatures, in fact, may be the reason that whirling disease hasn't been as severe a problem in the lower Madison as the upper Madison. Young fish are especially susceptible to whirling disease when the water temperature averages in the 50s F, especially in their first 90 days of life.

"In 10 to 12 years, the amount of data was impressive," Vincent said. "We went from no data to a pretty good handle on what's gone on."

The researchers hadn't come up with a solution, however. In the past 18 years, whirling disease has spread across the state, and the infection rate in the Madison River still ranks at four or five. A five rating means the infection is "exceedingly severe."

Despite the gloom, Vincent and his collaborators remain positive.

The crash that didn't come

"There's hope," said MSU ecologist Billie Kerans. "There's some hope for the trout in Montana. Not all drainages have responded the same way to whirling disease."

Vincent said, "The worst case scenario was drawn and didn't happen in Montana."

Scientists predicted, among other things, that the rainbow trout population in the Missouri River would crash, but it didn't. Not sure why, Vincent said it could be related to the size of the river and the large number of tributaries it has. Some juvenile trout may be safe because they swim in uninfected areas of the river.

The biggest surprise is that the rainbow trout population has started to rebound in the Madison River, Vincent said. Despite the high rate of infection and significant inbreeding, the rainbow trout population is now 60 to 70 percent of what it was before the population started to crash in the early '90s. He doesn't know of any other stream in the Intermountain West that has recovered on its own.

"Clearly, we got lucky," Vincent said. "If it hadn't been for resistance, it wouldn't be looking like it did. Who would have guessed?"

Despite the high rate of infection and significant inbreeding, the rainbow trout population is now 60 to 70 percent of what it was before the populations started to crash in the early '90s.
Vincent announced four years ago that whirling disease researchers had found rainbow trout that were somewhat resistant to whirling disease. The fish live in the Willow Creek Reservoir, three miles east of Harrison in Madison County. Their ancestors came from Wyoming between 1977 and 1981. In the century before that, they came to Wyoming from somewhere along the West Coast. They made the trip by train, riding in milk cans filled with water.

Vincent said he tried unsuccessfully to learn more details about the West Coast relatives. Despite his detective work, he knows they were wild trout, but doesn't know the state or stream where they originated. It was common back then, he added, to scoop wild fish out of streams during spawning and dump them elsewhere.

"In the late 1800s, fish were hauled everywhere, whether they needed it or didn't," Vincent said. "It was willy-nilly."

The Willow Creek trout resulted from that type of action.

"They are not absolutely resistant, but they are significantly resistant," Vincent said.

The trout were sent to scientists in Utah, California and Colorado for study, but no one intentionally planted them in the Madison River, Vincent said. He thinks the Madison River rainbow trout population may be rebounding because the Willow Creek trout somehow made it into the Madison. How they got there remains one of the great mysteries in the saga of Whirling Disease in Montana. Vincent said that some of the Willow Creek fish were stocked in Hebgen Lake and Ennis Lake, so it's possible that some of the fish floated over the spillways into the Madison. No one knows for sure, however.

What's next?

MSU researchers who have worked with Vincent on several research projects are in the process of writing a comprehensive report that will be finished this spring. The authors include Kerans and ecology professor Tom McMahon. Kerans is a Tubifex tubifex expert who came to MSU in 1996 to work on whirling disease. The report will describe how the Whirling Disease Initiative came about and what worked, Kerans said. The researchers will see how the initiative can serve as a model for studying other diseases caused by parasites.

McMahon and Kerans also will use FWP data to characterize the whirling disease risk in several drainages across Montana. The MSU researchers want to see if they can correlate that information to major environmental factors such as landscape, Kerans said.

The comprehensive report and drainage study are two parts of a three-part project, Kerans said. The final part looks at rainbow trout populations before and after whirling disease hit. Then it analyzes the effect that specific events, such as drought or whirling disease, had on those populations.

"Many managers and people in general felt you couldn't really separate the effects of whirling disease from some of the other events, and this analysis should help separate the different effects," Kerans said.

Whirling disease was really one of the first cases in freshwater where we are really looking into the effects of a disease or parasite in the wild.-Billie Kerans, MSU Ecologist
When the researchers finish their reports, they will submit them to Gretchen Rupp, director of the Montana Water Center that is based at MSU. Rupp then will combine their reports with those from other states and give them to the U.S. Fish and Wildlife Service. Whirling disease funding has declined over the years, but Kerans said she is optimistic about the future of Montana's streams and rainbow trout. She added that the whirling disease research has implications on other parasitic diseases, too.

"There's a nationwide push on to understand the ecology of emerging diseases," Kerans said. "Whirling disease was really one of the first cases in freshwater where we are really looking at the effects of a disease or parasite in the wild."

As whirling disease research continues without him, Vincent said he plans to enjoy his retirement. He and his wife began raising and showing miniature dachshunds several years ago and, so far, have raised 32 dogs that became American Kennel Club champions. Vincent is also thinking about fishing again. The idea held no appeal after his two summers as an undergraduate angler, but he is warming up to it.

"My wife loves to fish," he said. "She now believes we are going to do some more fishing. I believe she is correct."