Fall population estimates for the Snoball section have not been collected as consistently as in 

 Pine Butte. There are no data for 1986, or 1988 to 1993 for the Snoball section. However, 

 population comparisons may still be made between the two study sections. Relative abundance 

 shifts in the mid-1990's from a predominance of rainbow to brown trout in the Snoball section 

 just as it did in the Pine Butte section (Figures 16 and 17). The dramatic decline in rainbow trout 

 numbers is also apparent in the Snoball section where populations fell 83% from a mean of 3,304 

 fish per mile (1975 to 1987) to a mean of 571 fish per mile (1994 to 1997)(Figure 17). 



^"^ / / ^c^'^ ^^"^ ^^ ^^ ^^ ^cf ^c,^^ ^^ / ^"^ ^^^ ^"^ ^c?^ 



Year 



Figure 17. Fall population estimates for the Snoball section of the Madison River, Montana from 1975 to 

 1985, 1987, and 1994 to 1997. Estimates are derived from mark-recapture data for electrofishing nms, 

 and include all age classes offish (FWP 1995d, 1996c). 



5.3 Impacts of Whirling Disease and Management Implications 



The declines in catch rates documented by the 1995 and 1996 creel surveys, when examined with 

 the coincident declines in rainbow trout populations as measured by FWP annual surveys 

 provide a strong argument that whirling disease has had a heavy biological impact on the 

 Madison River fishery. The declines in the rainbow trout population are the most extreme, but 



Evaluation of 1995 and 1996 Creel DaU and its Implications related to Whirling Disease 

 In the Madison River, Montana 



29 



Montana Fish. Wildlife and Paries 

 March 12. 2002 



