considered a better indicator of the overall trout population trends (P. Byorth, pers. comm.. 

 2001). 



Figure 16 illustrates that the decline of the rainbow trout abundance coincided with the declining 

 catch rates in 1995 and 1996 creel surveys. Mean rainbow trout abundance declined 77% in 

 1991, suggesting that whirling disease was beginning to affect the fishery (Figure 16). Rainbow 

 trout populations fell fi-om a mean of 3,944 fish per mile (1975 to 1990) to a mean of 903 fish 

 per mile (1991 to 1996)(Figure 16). This decline is echoed in the greater than 60% decrease in 

 catch rates in post- whirling disease creel surveys as compared to earlier surveys from the 1970's 

 and 1981 (Figure 10 and 11). 



7,000 J- 



6,000 



5,000 



1 4,000 

 I 

 -§ 3,000 



2,000 



1,000 



Year 



Figure 16. Fall population estimates for the Pine Butte section of the Madison River, Montana from 1977 

 to 1996. Estimates are derived from mark-recapture data for electrofishing runs, and include age 1 and 

 older trout (FWP 1995d, 1996c). 



Relative abundance of brown trout increased fi-om 1977 to 1996 in the Pine Butte section (Figure 

 16). BrowTi trout numbers have not varied substantially throughout most of the years surveyed, 

 but appear to be increasing recently in the Pine Butte section (Figure 16). 



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

 In the Madison River, Montana 



28 



Montana Fish, Wildlife and Parks 

 March 12, 2002 



