YCT Multi-state Assessment February 10, 2003 



Ranked Risks to Conservation Populations 



We rated risks to 195 designated YCT conservation populations by miles of habitat occupied 

 (Table 13 and Figure 8; Appendix F) and by number of populations (Table 13 and Figure 9; 

 Appendix F). The two distinct types of conservation populations, "isolets" and "meta- 

 populations", were separated in the analyses. In general, isolet populations were at higher risk 

 than due to temporal variability (amount of occupied habitat), population size, and isolation 

 meta-populations, especially when rated by number of populations (Table 13), but isolet 

 populations were at less risk than meta-populations due to genetic introgression. Risks 

 associated with demographic factors were about the same for "isolates" and "meta-populations. 

 These findings validate the fact that while smaller, isolated populations are usually much more 

 susceptible to population level risks due to isolation, small population size, and temporal 

 variability; their isolation makes them less susceptible to genetic introgression. Conversely, 

 while more meta-populations (larger, connected populations) were less vulnerable to population 

 risks such as temporal variability, isolation, and small population size, their connectedness made 

 them more susceptible to genetic introgression risks (Table 13). Composite population risk 

 scores ranged fi-om a low of 4 to a high of 16 with most scores being over 10 for isolet 

 populations and under 8 for meta-populations (Figure 10). "Isolets" were at moderately high risk 

 based on the composite of risk characters. Meta-populations were viewed as being at moderately 

 low risk when all, non-genetic, risk factors were considered. It is important to note that 101 

 YCT conservation populations (5 1 .8%) were sympatric with compefitive species of trout. By 

 convention, the demographic risk factor associated with populations that were sympatric with 

 competitive species had to be rated down by one to two points. 



It is important to understand that population risks are presented in relative terms. Higher genetic 

 risk ratings for meta-populations do not mean that each of these population is doomed to a fate of 

 being genetically contaminated. Nor do high isolation risk ratings mean that all isolated 

 populations will be eventually eliminated. The risks evaluated in tliis review stiould be 

 viewed in relative terms and not as absolutes. 



Restoration Activities Implemented for Conservation Populations 



Restoration, conservation, and management activities that have been implemented to conserve 

 designated conservation populations were evaluated for the 195 conservation populations (Table 

 14). Angling restrictions have been implemented on waters that affect nearly half of the 

 designated conservation populations. Angling restrictions often consisted of "catch and release" 

 fishing for YCT, but other restrictions such as bag and size limits and gear restricdons were also 

 included. Restoration and enhancement activities, such as physical removal of competing and'or 

 hybridizing species, populafion restoration and expansion, riparian fencing, pool development, 

 diversion modification, riparian restoration and stream bank stabilization, have occurred for 5 to 

 10% of the conser\'ation populations, respectively. In addition, a substantial number of 

 conservation populations reside within the boundaries of lands with special management (e.g. 

 road less, wilderness, and national parks, etc.). 



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