cutthroat and rainbow trout with a much more substantial rainbow trout genetic 

 contribution. < , . , ..; .- -. ■ 



Sample 2923 suggests of the above two explanations the latter is more likely. This 

 sample (N=68) consisted mainly of migratory- adults collected from above and below 

 Ward Ditch in 2003 and 2004. PINE fragments characteristic of rainbow trout were 

 detected at three of the six diagnostic loci analyzed that usually distinguish rainbow trout 

 from westslope cutthroat trout. The rainbow trout markers appeared to be randomly 

 distributed (P>0.05) among the fish in the sample suggesting these fish came from a 

 hybrid swarm between westslope cutthroat trout and rainbow trout with about a 99.5% 

 westslope cutthroat trout genetic contribution. The previous Ward Ditch sample, , ; 

 therefore, may have been a mixture of Skalkaho Creek migratory fish and possibly a 

 migrant individual from a more heavily hybridized population, possibly the Bitterrroot 

 River. 



The question remaining in Skalkaho Creek, therefore, is whether or not the very upper 

 reaches of the stream actually still contain a non-hybridized westslope cutthroat trout 

 population or not. This possibility exists as samples 23 12 and 2923 all came from lower 

 reaches of the drainage and these upper reach fish are suspected to mainly express a 

 resident life history characteristic (Chris Clancy, Montana Department of Fish, Wildlife, 

 and Parks, personal communication). 



West Fork Bitterroot River (#710, #948, #1031?, #1032, and #2259) 



Samples 710 (collected September 6, 1992, N=3, T3S R22W SI 6) and 948 (July 18, 

 1994, 16, T3S R22W S4) were collected above Painted Rocks Reservoir. Allozyme 

 analysis indicated no evidence of hybridization. There was no evidence of genetic 

 differences between the samples (P>0.05) so they were combined into one. With the 

 combined sample size of 19, there is about a 90% chance of detecting as little as a one 

 percent rainbow trout and a 98% chance of detecting as little as a one percent 

 Yellowstone cutthroat trout genetic contribution to a hybrid swarm. At the time these 

 samples were collected, therefore, the upper West Fork Bitterroot River very likely 

 contained a non-hybridized westslope cutthroat trout populafion. 



Samples 1302 (September 21, 1998, 6, T2N R21 W S24) and 2259 (September 17, 1998, 

 25, TIS R22W S23) were collected below Painted Rocks Reservoir. Allozyme analysis 

 of the most downstream sample (1302) provided no evidence of hybridization. There 

 appeared to be a problem with DNA quality or extraction from sample 2259 as PINE data 

 were obtainable from only 14 fish. Of these, 12 possessed PINE fragments characterisfic 

 of only westslope cutthroat trout, one possessed a PINE fragment at one of the six 

 diagnostic loci that usually distinguish rainbow from westslope cutthroat trout, and the 

 final fish appeared to be a first generafion hybrid between westslope cutthroat and 

 rainbow trout as it possessed PINE fragments characteristic of both fishes at all marker 

 loci analyzed. Interpretation of these results is confounded, because the samples do not 

 represent a random collection offish. Rather individuals that morphologically appeared 

 to be westslope cutthroat trout were specifically collected (Chris Clancy, personal 



