their ramifications to overall Madison River ecology should be noted as well. Rainbow trout are 

 a food source for osprey, otters, and other predators that live in the area. Although the proportion 

 of brown trout has increased within the fish assemblage, total numbers offish have not; 

 therefore, the available prey base has decreased. Although predators may choose to move to 

 better foraging areas, fewer fish in the Madison may translate into proportionally heavier 

 predation on remaining fish which may also be weakened by whirling disease. The fishery also 

 plays a role in the larger ecosystem, and changes within the river will have an effect on the 

 surrounding biological community. 



Although not as dramatic as the trout population declines, the decrease in angler use recorded in 

 the FWP mail-in survey suggest that anglers have avoided the Madison River because of lower 

 fishing success and/ or a perceived decline in the river's overall merit as a fishing destination. 

 This translates into a potentially large economic impact due to the disease. 



The Madison River is an important sport fishery and recreational resource for the state and 

 generates considerable income annually fi-om guided and independent fishing trips and 

 associated recreation. According to Duffield (1990) the Madison River produces the highest non- 

 market fishery value per mile (annual basis) in the state at $184,000 per mile. This estimate is 

 based on value per angler day (derived fi-om travel cost model estimates) times the total angler 

 use quantified for each Montana stream (Duffield 1990). As a point of reference, the total 

 economic value of each stream in 1985 ranged fi-om $17.5 million per year on the Madison to 

 $53 1,000 on the Swan (Duffield 1990). It should be noted that these estimates were for a period 

 prior to the noticeable impact of whirling disease. Dr. Duffield has examined post-1990's data to 

 estimate the economic effect of whirling disease and found that the existence of the brown trout 

 fishery may have diminished the overall economic impact (Duffield et al. 1999). In his 1999 

 report he states that, " the combined (rainbow and brown) trout population, while about one- 

 third below the 1983- 1990 population, still places the Madison among the very top rivers in the 

 state". 



In addition to the possible economic impact due to whirling disease, the Madison is a large 

 tributary to the Missouri River and provides a connection with the Jefferson and Gallatin rivers 



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

 In the Madison River, Montana 



30 



Montana Fish, Wildlife and Parks 

 March 12, 2002 



