Fighting whirling disease

Defying gravity is a passion of humans. We're in awe of the act. Astronauts are our heroes, and airplane pilots are our idols. Maybe that's part of the reason why fishermen hold rainbow trout in such high regard. Rainbows are leapers.

Hurling themselves out of the water for anglers is one of the things rainbow trout do best. This leaping ability has brought them fame and fortune. But so has their availability to ordinary anglers such as you and me.

Today, rainbow trout are found almost everywhere in the West, including Wyoming, the Great Lakes and the East, Canada, cold streams throughout the South and cold stretches of rivers below dams in Texas, Oklahoma, Tennessee and Arkansas. More than other trout species, rainbows have proven they do well in a wide variety of habitats and climates. They are found in shallow and deep lakes, in small and large streams, in several of the Great Lakes and in some saltwater areas. All rainbows really need is cold, clean water, but they even survive in marginal conditions in some places.

Rainbows have a weakness, though. Rainbow trout are more susceptible to whirling disease than any other species of trout. In the 1990s, fisheries managers in Montana and Colorado discovered the disease's effects on their rainbow trout. What they've found has generated hysteria, paranoia and the largest effort to control a fisheries disease in modern history. Montana's and Colorado's situations are being watched by other states, including Wyoming, who more and more, are detecting the presence of the whirling disease parasite in their waters. Some states are merely watching and monitoring their waters. Other states, including Wyoming, are aggressively and attempting to keep the parasite from invading hatcheries and from spreading further into valuable wild-trout waters.

Montana's Madison River was the model of a wild trout fishery before 1991. But in the fall of 1991, fisheries workers documented declines in wild trout numbers in the Pine Butte section of the river. The decline was unusual, because it only affected wild rainbow trout. Two years later, workers noticed another decline in wild rainbow trout almost thirty miles downstream in the Varney study section. By the fall of 1994, rainbow trout numbers had declined almost ninety percent in both study sections from historic averages in the 1970s and 1980s. Brown trout numbers were stable in this same period.

In December 1994, Montana fisheries workers collected young-of-the-year and yearling rainbow and brown trout from the Madison River from Quake Lake to Ennis Lake. The fish were tested for diseases, including whirling disease. A few weeks passed, and the confirmation came - some of the young trout were positive for whirling disease (Myxobolus cerebralis) spores. Samples taken in the fifty-five-mile reach of the river showed spores in up to seventy-five percent of the young fish that were examined. This was the first time whirling disease had been documented in Montana.

In 1995, an electrofishing survey of the Pine Butte and Snoball study sections of the Madison River documented clinical signs of whirling disease in Montana's wild rainbow trout. Clinical signs of the disease, such as head and body deformities, black tails and whirling behavior, were noted in up to fifty percent of the young-of-the-year rainbow trout. Young brown trout showed only light infections while rainbow trout infections were more severe.

Since 1994, the Montana Department of Fish, Wildlife and Parks has surveyed for the parasite in state waters through electrofishing, gill nets, fish traps and angling. Nearly 30,000 fish from more than 350 waters, including twenty-two hatcheries and some private ponds, have been tested for the presence of the whirling disease parasite.

To date, the parasite has been found in 73 Montana waters in 10 of 22 major river drainages. Montana's nine state, three federal, and 10 private hatcheries are not infected with whirling disease, nor have they ever been.

And although whirling disease poses no threat to humans who eat infected fish, the disease has affected Montana's income from trout fishing, which brings in about $250 million a year to the state.

Colorado first discovered whirling disease in 1988. At that time, Colorado Division of Wildlife scientists didn't believe the parasite was devastating, and they believed it could be controlled.

In 1993, Colorado fisheries workers found that young-of-the-year age classes of rainbow trout were missing from sections of the upper Colorado River. The cause: whirling disease. Since then, whirling disease has been found in parts of 14 of 15 major river drainages in the state. Losses of young fish have been documented in sections of the Colorado, South Platte, Poudre, Gunnison and Rio Grande rivers. Up to 300 of Colorado's 7,000 miles of streams may show population effects from the parasite.

Testing also revealed that whirling disease had infected eight of ColoradoÕs 11 fish hatcheries. Prior to the findings, these hatcheries were producing more than 4.5 million catchable rainbow trout each year, and two million of these were being stocked on Colorado's West Slope.

Upon finding the disease, Colorado shut down rainbow production at some of these facilities and cut back production at others.

In 1994, before whirling disease was recognized as a threat to wild trout by Colorado, 125 rivers and streams were stocked with trout exposed to the parasite. By 1997, that number was reduced to portions of the Arkansas, Cache la Poudre, Colorado, East, Gunnison and South Platte rivers.

In 1996, Colorado adopted a new stocking policy that only allows trout testing negative for whirling disease to be stocked in waters that test negative for the disease. As a result, out of three million catchable rainbows produced in hatcheries last year, only 200,000 whirling disease-negative trout were stocked in West Slope waters. Whirling disease-exposed fish were stocked in eastern Colorado, however, where the parasite is already found.

Cuts in stocking has forced Colorado to reduce angler limits. The lower limits apply to waters west of the Continental Divide where the daily limit is two trout from streams and four trout in reservoirs and lakes. Colorado also added special catch-and-release regulations for new cutthroat waters on the West Slope and Rio Grande drainage.

Colorado is spending millions on its war on whirling disease, too. Colorado's legislature approved $10 million for the Division of Wildlife to spend on the first phase of its hatchery cleanup project, and the wildlife agency may seek up to another $10 million to fight the disease. Colorado is spending its money on six hatcheries that have the potential to be rid of the parasite— Mount Shavano, Finger Rock, Roaring Judy, Rifle Falls, Bellvue and Durango. The agency is focusing on cleanup of hatcheries that have secure ground water sources; hatcheries that rely totally on surface water may not be rehabilitated.

The effort is paying off, too. One Colorado hatchery, Mt. Ouray, has been certified negative for whirling disease through DNA testing, and two more (Bellvue and Durango) have initially tested negative for the disease. The success at Mt. Ouray is encouraging in that the parasite was first found there in 1986.

Colorado scientists are unsure if the hatchery improvements will totally purge the parasite, but they believe the improvements will eliminate the chances of other diseases entering the hatcheries. If the hatchery improvements proceed on schedule and testing remains negative for whirling disease, these hatcheries could be producing 1.9 million whirling disease-negative, catchable trout every year by 2002.

There is also evidence that suggests whirling disease may be involved in population declines in Idaho's Big Lost River and Utah's Beaver River. Other rivers in Idaho, Utah, Wyoming and other states, including New York, have the parasite, but they have not experienced declines in fish populations.

Idaho has had some problems with the parasite in at least three of its hatcheries.