appeared hybrid in this sample was a post-Fl hybrid, indicating that an extremely low 

 level of hybridization has been occurring for generations. 



Since this sample was collected from the main stem of the Bitterroot River, it is 

 not valid to report genetic contributions of the component species at the population level, 

 as it is likely that the individuals come from several different populations. 



It is important to note that with the small sample size of this population, the 

 accuracy of this estimate is limited until further data is available. Also, collection of 

 samples from spawning tributaries can provide a better picture of the extent of 

 hybridization within those streams, rather than individuals from a main stem stream. 



Butte Cabin Creek: Only nine individuals in this sample displayed PINE fragments 

 diagnostic of vvestslope cuttliroat trout. These individuals also displayed characteristic 

 Yellowstone cutthroat trout markers and rainbow markers. The remaining 16 displayed 

 Brown trout PINE fragments. 



Game Creek: All individuals in this sample exhibited fragments diagnostic of westslope 

 cutthroat trout. However, individuals 1-2 and 1-8 displayed a single Rainbow trout 

 diagnostic marker at one locus. The presence of this marker in the sample could indicate 

 hybridization with rainbow trout or alternatively it could be a rare westslope cutthroat 

 trout variation. In this situation, we favor the latter since if the presence of this fragment 

 was due to hybridization, then we usually expect to observe fragments at other diagnostic 

 loci characteristic of rainbow trout in frequencies similar to the former. This, however, 

 was not the case. With 24 individuals, we have an 85% chance of detecting 1% 

 hybridization with rainbow trout. It is possible that this population may be hybridized 

 with Rainbow trout. However, unless further data indicate otherwise, the conservative 

 approach would be to treat the population as westslope cutthroat trout. 



First Creek: All successfully analyzed individuals in this sample exhibited fragments 

 diagnostic of westslope cutthroat trout only. With a sample size of 18, we have a 76% 

 chance of detecting 1% hybridization with rainbow trout using 4 markers. This sample 

 appears to have come from a pure westslope population, but with the small sample size, 

 we cannot reasonably conclude the possibility that it might be slightly hybridized with 

 rainbow trout. Unless further data indicate otherwise, it should be managed as a 

 westslope cutthroat trout population. 



Douglas Creek: All individuals in this sample exhibited fragments diagnostic of 

 westslope cutthroat trout only. With a sample size of 24, we have a 94% chance of 

 detecting 1 % hybridization with rainbow trout using 6 markers. Unless further data 

 indicate otherwise, it should be managed as a westslope cutthroat trout population. 



Hogback Creek: All successfully analyzed individuals in this sample exhibited fragments 

 diagnostic of westslope cutthroat trout. However, nine of the 19 samples also displayed 

 diagnostic rainbow markers. The individuals that appeared hybrid were all post-F] 

 hybrids, indicating that hybridization has been occurring for generations. Assuming 

 random mating proportions, the genetic contribution of westslope cuttliroat trout and 

 rainbow trout is 75% and 25%, respectively. 



