A recent public opinion survey sponsored by the Colorado Division of Wildlife indicated that over 70% of licensed Colorado anglers are aware of whirling disease (WD). With this level of awareness it is time to move on to the next step of understanding what is being done about it and how these actions impact our fishing resources.

WD comes from a parasite known as myxobolus cerebralis. The parasite invades salmonid species and attacks the cartilage of very young fish. The result of the invasion leaves young fish with crooked tails and backs that cause the fish to spin when swimming, thus the name WD.

It was first documented in Colorado in 1987, although it has been in the United States since the 1950's and believed to have come from Europe in a shipment of frozen fish. The parasites made their way into at least seven of Colorado's hatcheries and five of our seven river drainage's. Colorado began stocking fish in 1881 and over 10 million rainbows are now stocked annually.

German browns became resistant to the effects of WD long ago, but most rainbow's are very susceptible. It has been discovered that entire age classes of rainbow's have disappeared in Colorado as a result of the disease.

WD has been indentified in at least 20 states. Many western states are trying a variety of techniques to deal with the problem while some do not regard it as threat.

Arizona has certified their hatcheries as WD free but expect the disease to spread and are on the lookout.

Wyoming has found WD in the North Platte river drainage but they do not believe it is a problem at this time.

California, Idaho, and Oregon have all confirmed the existence of WD in their fisheries, but have yet to see any adverse effects from the disease.

Montana, Utah, and Colorado all consider WD to pose a severe threat and are currently formulating policies to deal with the problem until it is solved.

Montana has reported the loss of 91% of the rainbow population between 1991 and 1994 in the Madison River. The loss has been attributed to WD. Montana maintains a no-stocking policy and therefore, may be at greater risk from the disease than other states.

Utah is experimenting with a radical plan where they kill all fish in a stream annually with rotenone and then restock with WD negative fish. The theory is by interrupting the life cycle of the parasite it will eventually die off. Early reports indicate they are having some success.

In Colorado, the infected hatcheries are being purged of the parasites. At least one hatchery will be retrofitted with the installation of ultraviolet lights designed to continually rid the water of the parasites.

Colorado also inacted a fish stocking moratorium last year and WD negative waters have been banned from the stocking program. This created a fish surplus and when the moratorium ended in July many WD positive waters received additional numbers of WD exposed or infected fish.

The C.D.O.W. has allocated additonal funds ($600,000) for WD research and the acquisition of another aquatics biologist to assist the Division's Barry Nehring and Pete Walker in the search for answers to the WD problem.

There will be an international Whirling Disease workshop held in Denver in February. This workshop is expected to provide many answers and management direction alternatives. It will include leading fish health experts from state and federal agencies, New Zealand, and Europe. The 2 1/2 day workshop is designed to allow the expected 400 participants to collectively tackle WD.

In May of 1995, Colorado's Wildlife Commission directed the C.D.O.W. to assign a "citizens" work group the task of determining alternatives to the stocking of fish exposed to whirling disease. The proposed stocking alternatives of this group will be reviewed after the WD workshop and finalized.

The Whirling Disease Work Group (WDWG), as it is called, has worked during the past several months to formulate a draft of the possible alternatives. The following is an overview of the WDWG "draft" alternatives:

"The goal of any stocking program should be to maintain the maximum protection of aquatic resources containing salmonids that do not have whirling disease."

WDWG recommendations on stocking:

• There should be no stocking of fish exposed to WD in flowing or standing waters that are considered to be WD negative.
• There should be no stocking of fish exposed to WD in standing waters located upstream of flowing waters with salmonid populations considered to be WD negative.
• There should be no stocking of fish exposed to WD in protected habitats as currently defined (see definition) by the Director of the C.D.O.W.
• The definition of "protected habitat" should be clarified to include the waters necessary for the protection of a) designated wilderness areas; b) native cutthroat trout recovery and management waters; c) unique coldwater resources designated by the Division.
• Fish exposed to, or infected with high (greater than 100,000) or medium (10,000 -100,000) levels of whirling disease may be stocked into zero-impact waters ( dead - end waters) where there is minimal possibility of waterborne transmission of spores.
• Fish exposed to, or infected with light levels ( less than 10,000 ) of spores may be stocked into WD positive waters, in accordance with guidelines expressed in recommendation number 4.

The "draft" alternatives are expected to change somewhat after the Whirling Disease conference in Denver. It is hoped the conference will shed new light on the WD problem and provide many answers. The WDWG will meet shortly after the conference and finalize the recommendations. The final plan will be submitted to the Wildlife Commission for them to possibly adopt as a policy.

The adoption of these alternatives will obviously have a significant impact on our fisheries. And yes, Colorado is hard at work trying to find the answers to WD, as are many states. It is clear that Colorado must clean up the hatcheries and our infected waters or face severe consequences.

The disease is spreading and without some answers all of our fisheries are endangered. Colorado's population will reach 4 million by the year 2000 and projected to grow to 5 million by 2020. With this increase in population comes increased pressure on our already heavily burdened resources. Continued disappearances of age class fish and the possible cut back on stocked fish to supplement this loss, will undoubtedly result in drastic changes in trout fishing in Colorado.

Mike Miller - The Colorado Fishing Federation 

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