Whirling Disease Update September 1, 2003

In the mid 90's, whirling disease was discovered in several western trout streams and was linked to the dramatic decline in trout population. Since that time, the disease has been detected in 23 states and continues to worsen and spread to new waters.

For the first few years, scientists focused on filling in the basic knowledge gaps about the life cycle of the parasite, the alternate host tubifex worm, and the susceptibility of the trout and salmonid host. In the past 2-3 years, the research focus has shifted to applying the new found knowledge to managing the disease. While there does not appear to be a "silver bullet" capable of eradicating the parasite, there does appear to be several viable management options which could help to control the level of the infection. It is likely that managing the disease will be accomplished by applying methods from a palette or matrix of different management choices to a particular river.

In 2000, the Whirling Disease Foundation was approached by two leading whirling disease researchers with information that a strain of rainbow trout from North America that had been introduced into a family owned trout hatchery (Hofer) in Germany, 150 years ago, may possess a high degree of resistance to whirling disease. The Foundation provided the initial funding for this project which began with a laboratory test of the Hofer rainbow. The initial testing proved that this rainbow possessed a high degree of resistance to the disease, and phase 2 of the research found the Hofer rainbow to be no more or less susceptible to other North American trout and salmon diseases. The third phase of the resistant trout research is now underway, and includes work utilizing traditional animal husbandry techniques of crossing the resistant Hofer rainbow strain with other strains of susceptible North American rainbow trout. This is not "genetic engineering" but is simply utilizing traditional breeding methods. The desired outcome of this phase would be to identify offspring that possesses the desired qualities of the North American rainbows i.e. appearance, sporting qualities, ability to spawn and survive in the wild, etc., with an increased resistance to whirling disease. These fish could then be used to restore and replenish wild rainbow stocks that have been decimated by the disease. Quite recently, research in Montana revealed that another strain of rainbow trout, the Desmet rainbow, may also possess a high degree of resistance. The states of Montana and Utah have begun research into the resistance of the Desmet rainbow, and the Whirling Disease Foundation is working closely with the states of Montana, Utah, and Colorado to integrate the Desmet research into the overall resistant trout research plan.

In addition to the resistant trout research, there are several other promising management options that are receiving funding through the WDF. In Colorado, a wetlands filtration system is being tested that could remove the fish infective form of the whirling disease parasite from a heavily infected tributary of the Frying Pan River. The initial phase of this filtration project research proved effective, but the initial design required a great deal of maintenance. The new, natural wetlands filtration system that is currently being tested could provide a natural method for managing the disease in infected tributaries with a low flow rate.

Research on Montana's Madison River indicates that raising river flows at the time of the emergence of rainbow trout fry from spawning gravel beds could dilute the concentration of the parasite and thereby lower the level of whirling disease infection in the trout. Such flow manipulation could occur on dam controlled rivers and could be a part of the management matrix.

Alternate Host Tubifex Worm Research

It has been discovered that populations of the alternate host Tubifex worm thrive under certain environmental conditions. Several habitat restoration projects, including a project about to begin on Upper Willow Creek, a heavily infected tributary of Rock Creek near Missoula, could prove that restoring and repairing stream habitat will help lower the level of whirling disease infection.

Although there has not been a great deal of recent publicity regarding the negative impacts of the disease, whirling disease continues to cause severe problems in many western states. Low water levels are known to exacerbate the disease by concentrating the parasite and high water temperatures increase the rate of disease in the fish. As you know, we have been in a severe drought situation in the West, and this has caused whirling disease infections to escalate in many waters. In Montana, the disease continues to cause problems in the Madison River. Following two good year classes of surviving rainbows in the Madison in 1998 and 1999, the years following have been very, very poor with survival rates similar to the poorest previous years. In the Missouri river near your home, the infection in Prickly Pear has escalated to extremely high levels and is so severe that virtually no juvenile rainbows reared in Prickly Pear survived. As a result, the infection in the Missouri main stem has increased to the point that it is causing population declines. The worst news on the Missouri is that the Dearborn River, which had not shown evidence of the infection, is now WD positive and the infection level is increasing. This is very bad news for the Missouri as the spawning and reproduction in the Dearborn had been holding up the Missouri River rainbow population. In addition, whirling disease infections are increasing in the Smith River, the Blackfoot, the lower Clark Fork, Rock Creek near Missoula, and in the East Gallatin near Bozeman, to name just a few.

Colorado continues to suffer heavy infections in many of its rivers and streams. In Wyoming, a whirling disease infection has caused the closure of an important hatchery. Utah continues to have severe problems with whirling disease in many waters, and whirling disease recently arrived in New Mexico and threatens reintroduction programs for the native Gila and Apache trout. For the past few years, the Yellowstone cutthroat populations in the Park have been declining. This decline had been largely attributed to the predation by lake trout on cutthroat fry returning to Yellowstone Lake from spawning tributaries. It has been discovered that several key Yellowstone Lake tributaries suffer from whirling disease infections. Pelican Creek, one of Yellowstone's most famous cutthroat streams is so severely infected that scientists have been unable to find even a single juvenile cutthroat from recent year classes. In short, even though we have not heard as much about the disease in the media, things are not getting better. The trout need your help! The Whirling Disease Foundation requests your continued support for the work of the Foundation, for the research being conducted by state fish and wildlife agencies and colleges and universities, and for the necessary funding provided by state and federal agencies and conservation organizations. Thanks!

Whirling Disease Foundation

POB ~327

Bozeman MT 59771-0327

406-585-08602

website www.whirling-disease.org email whirling@mcn.net