YCT Multi-state Assessment February 1 0, 2003 



reproductively isolated from YCT, due to either temporal or spatial isolation during spawning, 

 the genetic risk rating for that conservation population was reduced. Normative salmonids that 

 could potentially hybridize with YCT. had been stocked, either legally or illegally and, were now 

 reproducing naturally in the wild were considered as posing a genetic risk to YCT. 



Table 3. Ranks and descriptions used for assessing genetic risks to designated conservation 



populations of Yellowstone cutthroat trout in 2001 . Hybridizing species includes any 

 introduced species or subspecies that could potentially hybridize with Yellowstone 

 cutthroat trout. 



Rank Acrivity 



1 Hybridizing species CANNOT INTERACT with existing YCT population. Barrier 

 provides complete blockage to upstream fish movement. No hybridizing species in close 

 proximity to YCT population. 



2 Hybridizing species are in same stream and/or drainage FURTHER THAN 1 KM from 

 YCT population, but not in same stream segment as YCT, or may be WITHIN 10 KM 

 WHERE BARRIER EXISTS, BUT THE BARRIER MAY BE AT RISK OF FAILURE. 



3 Hybridizing species are in same stream and/or drainage WITHIN 10 KM of YCT 

 population and NO BARRIER EXISTS; however, hybridizing species not yet found in 

 same stream segment as YCT population. 



4 Hybridizing species are SYMPATRIC with YCT population in same stream segment. 



Population Risks 



Demographic and stochastic population risks were assessed using criteria established by Rieman 

 et al. (1993). Four separate types of risk were considered including: temporal variability, 

 population size, population productivity, and isolation (Table 4). These four main factors were 

 assessed individually and then weighted and summed to derive a final composite risk factor. 

 Weightings were assigned to each risk factor based on advice from those who developed the 

 demographic and stochastic population risk matrix (Rieman et al. 1993; D. Lee, U.S.D.A. Forest 

 Service, Rocky Mountain Research Station, Boise, Idaho, personal communication) as: 

 Temporal Variability = 0.7; Population Size = 1.2; Population Productivity (Growth/Survival) = 

 1.6; and Isolation = 0.5. Weighted composite risk scores could potentially range from 4 to 16 

 and were then ranked into four low to high risk categories by placing them in four nearly equal- 

 sized bins (4 to < 7; 7 to < 10; 10 to <13; and 13 to 16). 



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