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

Thompson, Fryingpan, and Dolores rivers) which have tested positive yet have shown no
significant population impacts. DOW 's Aquatic Resources/Hatchery personnel estimate that the
range of the parasite may be expanding by about 5% per year (in Deloitte & Touche 1995).
Over the years, Colorado's hatchery system has had to deal with potentially devastating
problems such as diseases, water quality and quantity issues, and parasitic infestations. Until
recently, most fish pathologists believed WD would not negatively impact wild trout populations
(Anonymous 1988). This belief was based mainly on hatchery experience and the fact that there
were no published studies indicating otherwise. Results of the first study documenting the
impacts of a controlled quantitative exposure of very young rainbow trout to a very low dose of
the MC pathogen were published by Markiw in 1991. In hatcheries, WD is a malady that rarely
causes mortalities or leaves trout permanently impaired (Markiw 1992). Many fish pathologists
and fishery managers assumed if trout survived infections of the WD parasite in a hatchery, the
disease would not affect trout in the wild. This assumption was based on the belief that hatchery
conditions were undoubtedly more stressful than what exists in the wild environment. However,
the results in a recently completed study on the Colorado River (Walker and Nehring 1995;
Nehring and Walker 1996), as well as results of other investigations in Montana (Vincent 1996)
and Utah, clearly demonstrate that WD in the wild is a reality in the intermountain west.
Table 1. Approximate warmwater stream miles and surface acres, and coldwater stream miles
and surface acres in Colorado, and their "whirling disease" status.
WARMWATER COLDWATER
STREAMS LAKES STREAMS LAKES
N MILES N ACRES N MILES N ACRES
WD+' na na 44 6703 21 10,400
Other2 16 529 437 116,300 8,857 53,230 3,046 103,900
Total 16 529' T71 116,340 8,901 53,900" 3,067 114,300
'Waters where the presence of WD has been confirmed by statistically-valid testing.
'These numbers were obtained by subtracting WD+ data from the total. This group includes untested waters
and a small number of stream miles (<100) testing negative.
'A total of 2,550 miles have been exposed to WD by stocking; 670 miles have tested positive.
'Represents perennial and ephemeral streams.