Catch rates and harvest emphasize the predominance of rainbow trout in the fishery. 

 Cfttch rates of rainbow trout averaged nearly three times greater than brown trout catch 

 rates. An average of 0.3 1 rainbow trout were caught per hour overall while brown trout 

 catch rates averaged 0.09 per hour. Rainbow trout catch rates ranged as high as 0.5 fish 

 per hour which could be considered a very good catch rate for trout. Brown trout are 

 less catchable than rainbow trout in general. However, during ice melt in spring and ice 

 formation in fall, catch rates of brown trout peak. Mountain whitefish and Utah chub are 

 common in gill net catches (Byorth and Weiss 2002) but are rare in the anglers' creels. 



Size of trout in the creel was very similar between rainbow and brown trout. Brown trout 

 grew more slowly than rainbow trout but reached similar size by age 5. Hatchery 

 rainbow trout grew more quickly than wild rainbow trout, but older, larger wild trout 

 were more common in the creel than hatchery rainbow trout. Age 3 and 4 trout of both 

 species dominated the creel. The lack of Age 1 rainbow trout supports the contention that 

 wild rainbow trout rear in tributaries and are not available to anglers or gill nets. All age 

 1 rainbow trout captured by anglers were classified as hatchery fish. 



The contribution of hatchery vs. wild rainbow trout has been difficult to assess. In this 

 study, we attempted to compare dorsal fin erosion, scale checks, and tet-marks as 

 indicators of rainbow trout origin. Each method has inherent biases. If all methods are 

 considered, the proportion of hatchery rainbow trout in the creel averaged 19%, ranging 

 fi-om to 47% (Table 4). In general, dorsal fin erosion and tet-marks appear to be most 

 strongly correlated (Table 4). Using rainbow trout caught in gill nets either during or 

 immediately before the creel period, dorsal fin erosion indicated 16 to 28%) of rainbow 

 trout were of hatchery origin. However, tet-marks indicated to 6% were of hatchery 

 origin. It is clear that tet-marking efficiency is probably less than 10%. Assuming the 

 efficiency is 10%, then 30% of the fish in the creel could have been hatchery rainbow 

 trout. 



Scale check marks as an indicator of hatchery origin suggests the highest proportion of 

 hatchery rainbow in the creel (Table 4). However, it appears to be the most subjective 

 and least reliable. Unless more detailed analysis demonstrates specific measurable 

 criteria for classifying a scale "stocking" check, I would not recommend using this 

 method. 



Beginning in 2001, at least a third of all stocked rainbow trout have been marked with an 

 adipose clip. This should provide an absolute indicator of hatchery origin. When four 

 year-classes of adipose-clipped rainbow trout are in the population, a scaled back creel 

 survey should be conducted to reassess the contribution to creel and another analysis of 

 the methods of determining hatchery origin. Each rainbow trout with a clipped adipose 

 fin captured in gill nets or creeled by anglers should be classified according to dorsal fin 

 erosion, tet-mark, and scale check to determine the most robust method. 

 In any case, hatchery rainbow trout are probably contributing up to a third of the rainbow 

 trout to the creel. If this is the case, ceasing stocking may substantially impact catch rates 

 and angler satisfaction. Careftil assessment of opportunities to expand wild rainbow trout 

 recruitment should be completed prior to discontinuing stocking. A Montana State 



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