8057

• UCREFRP Catalog Number: 8057
• Author: Bennett, J. R., D. A. Krieger, T. P. Nesler, L. E. Harris and R. B. Nehring.
• Title: An Assessment Of Fishery Management And Fish Production Alternatives To Reduce The Impact Of Whirling Disease In Colorado.
• USFW Year: 1996.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

Whirling Disease
Myxobolus cerebralis (MC), the myxosporean fish pathogen that causes WD, was first
detected in public and private fish culture facilities in Colorado in 1987. Between 1988 and 1991,
despite massive field testing for the presence of MC, there was no evidence that the parasite
impacted wild trout populations. Moreover, containment and control of the parasite at public and
private fish culture facilities seemed to be working. However, beginning in 1992, additional state
fish culture facilities began to test positive for the parasite.
In late 1993 and continuing into 1994, circumstantial evidence indicated that WD was
potentially linked to serious declines in wild trout populations in the upper Colorado River.
During 1994 and continuing through 1995, DOW researchers, fish health specialists, and
biologists amassed significant evidence that exposure to MC was implicated in severe declines in
wild rainbow trout populations in several Colorado trout streams, including the Colorado, Cache
la Poudre, Gunnison, Rio Grande, and South Platte rivers. Moreover, sentinel fish tests in 1995
and 1996 demonstrated that Colorado River cutthroat trout and brook trout were even more
severely affected by exposure to the pathogen in the Colorado River than rainbow trout and
brown trout.
In response to the problem, the DOW has implemented steps on a number of fronts. These
include (1) greatly expanding the WD testing program with a large research effort at both the field
and laboratory level to assess the threat to wild trout populations; (2) determining the status and
rate of expansion of the disease in the wild; (3) initiating major efforts to clean up fish culture
facilities testing positive for the parasite as well as protecting the remaining negative units; (4)
dramatically redirecting the use and stocking of cultured fish in natural environments to stem the
spread of the parasite into presently negative habitats; (5) implementing long-term monitoring to
determine if it is possible to reverse the serious effects of the pathogen among some wild trout
populations presently being impacted severely by the disease; and (6) redirecting and reallocating
human resources and equipment. More than $700,000 was spent during fiscal year 1995-96 to
accomplish the above steps.
Protection
Native cutthroat and wild trout populations are a part of Colorado's natural wildlife heritage
and provide a recreational fishing opportunity that is held in high esteem by the public. Protection
of native species and self-sustaining wild trout fisheries from the adverse effects of WD is
considered paramount and should not be compromised to sustain recreational use levels. The fact
that two of the three native cutthroat species are declining or federally-listed due to other factors
makes this protection from WD even more compelling. Since native trout appear at least as
vulnerable to the pathogen as rainbow trout, lack of adequate protection would likely increase the
risk of further decline and frustrate recovery and conservation efforts.
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