YCT Multi-state Assessment February 10, 2003 



additional populations. Management will emphasize conservation, including potential 

 expansion, of both core and conservation populations. 



For this assessment any stream segment that supported YCT could potentially be designated as 

 either an individual "conservation population", aggregated as part of a larger networked or 

 connected "conservation population", or be considered as having recreational fishery value, but 

 not considered within YCT conservation. Designated "conservation populations" that occupied 

 two or more connected stream segments were viewed as population networks ("meta- 

 populations") that had the potential to interact with each other (Hanski and Gilpin 1991). 

 Populations were designated as "conservation populations" based on whether they represented a 

 core conservation population having no genetic alteration or there were identified unique 

 attributes such as expression of unique or multiple life-history strategies, adaptation to specific 

 environmental or habitat conditions, and geographic location (Anon 2000; Allendorf et al. 2001). 



Almost all stream segments occupied by YCT where genetic testing found no evidence of 

 introgression were classified as "core conservation populations". A few isolated stream 

 segments where YCT were genetically tested and there was no evidence of introgression were 

 not classed as conservation populations. These populations occupied very little habitat and it 

 was not deemed effective to invest in expanding them because expanding these populations was 

 infeasible given current restoration techniques. Some of these populations might be replicated 

 by moving either fish or gametes in the fiature, but this restoration activity would be speculative 

 at this time. 



Ail conservation populations were classified as either "isolates" or "meta-populations" 

 depending upon their isolation or connecfivity and likely genetic exchange between stream 

 segments. We also identified conservation populations that were considered as a "source" to 

 other conservafion populations. This information was felt to be potentially important to future 

 conservation decisions. 



We summarized information for designated conservation populations based on length of stream 

 occupied, number of populations, and geographic distribution. Since there was a very wide 

 range of lengths of habitats occupied by the various conservation populations we chose to 

 present these data in terms of length occupied and number of populations. 



Risk Classification 



The risks identified in this assessment are potential risks that could occur in the "foreseeable 

 future" (considered to be two to tliree decades). Risks were stratified into two major categories: 

 genetic and general population-level health. 



Genetic Risks 



GeneUc risk was defined by the risk of future introgression of YCT in a conservation population. 

 Distance from potential sources of anthropogenic introgression and the presence of documented 

 barriers between those sources and the conservation population were the two primary 

 components that were assessed to determine genefic risk (Table 3). In addifion, where there was 

 documented evidence indicating that potentially introgressing species or subspecies were 



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