YCT Multi-state Assessment February 10, 2003 



Genetic Status 



Genetic testing of YCT (both spotting forms combined) across all of the currently occupied area 

 has not been completed. Most genetic testing was not completed in random fashion. 

 Consequently, the available genetics information does not constitute a random sample taken 

 from the entire YCT population. Instead, there was a tendency to sample fish from populations 

 that appeared to be phenotypical YCT. Genetic sampling has been conducted in over 1 ,880 

 miles of occupied habitats (25% of occupied habitats). No evidence of introgression was found 

 from samples covering about 1,300 miles (69% of tested area, 17% of occupied habitats, and 7% 

 of historical habitats; Table 7; Figures 2 and 3; Appendix F). YCT that made up part of a mixed 

 stock population and were not introgressed occupied another 105 miles for a total of genetically 

 tested non-introgressed YCT occupying over 19% of currently occupied habitats. YCT that 

 inhabited over 3,018 miles (40% of occupied habitats and 17% of historical habitats) are 

 suspected of being genetically unaltered, based on the absence of introduced hybridizing species 

 and the lack of records that identify stocking of hybridizing species. YCT in about 2,629 miles 

 (35% of occupied habitats and 15% of historical habitats) were identified as having the potential 

 of being hybridized due to the presence, or past stocking, of hybridizing normative species or 

 subspecies (Table 7). 



To better evaluate the quality of genetic sampling, we looked at the sample sizes of genetic 

 sampling events related to whether more or less than a 1% level of introgression was found 

 (Figure 4). The number offish sampled represents each sampling event and, in some cases, 

 more than one sampling event were probably pooled, but we had no way of assessing pooled 

 samples. Of those samples that indicated a level of introgression of !%> or less, 21% had 25 fish 

 or more and over 48% had 20 fish or more in the sample. Most genetic testing techniques allow 

 for a 95% confidence at detecting a 1% level of introgression with a 25 fish sample. 



To provide insight into the likely genetic status of YCT within habitats classified as "Potentially 

 Unaltered" and "Suspected Altered" we refer the reader to the recent westslope cutthroat (WCT) 

 status review that was completed in February, 2003 (Shepard et al. 2003). For central Idaho 

 where limited genetic testing has been conducted, the assessment team took a closer look at 

 classificafion results for 10 separate 4th code HUC's where some genefic tesfing had been 

 conducted, they compared the level of introgression within tested stream seginents to the 

 classifications for stream seginents where no genetic tesfing had been done. Seven of these ten 

 HUC's had the majority of the stream segments classified as "Potentially Altered". Of these 

 seven, genefic testing in five HUC's found no evidence of introgression, while genetic testing in 

 one HUC found 65% of tested stream length had no evidence of introgression and testing in 

 another HUC found evidence of introgression in all tested samples. Conversely, some stream 

 segments in one HUC that supported WCT classified as being primarily "Suspected Unaltered" 

 tested as introgressed, while genetic testing in the other two HUC's that were predominated by 

 streams classified as "Suspected Unaltered" found no evidence of introgression. We feel the 

 situation for YCT maybe somewhat similar to that of WCT in that the potenfial for introgression 

 is highest in stream seginents that are connected to waters that support nonnative species or 

 subspecies that could interbreed with YCT. We caution against drawing specific conclusions 

 about genefic status of YCT populations identified as potenfially unaltered or suspected altered 

 from a genefic perspective. The definitive way of determining genetic status is through formal 

 genefic testing. 



Page - 1 7 



