YCT Multi-state Assessment February 10, 2003 



We separated the rated risks to the conservation populations based on spotting pattern by miles 

 of habitat occupied and by number of populations (Table 1 7). The distinct spotting patterns were 

 separated in the analyses. In general, spotting pattern did not appear to be related to genetic risks 

 to the populations. The difference associated with the low genetic risk for the fine spotted 

 populations was likely a function of the limited genetic sampling completed to date. Few clear 

 risk differences emerged during the analysis. We believe the risks assessed for YCT in general 

 also apply equally to the differing spotting patterns. Further comments or discussion of the two 

 spotting patterns of YCT will not be carried forward in the discussion and conclusions section. 



Discussion and Conclusions 



Historical Range 



The exact evolutionary (phylogenetic) origins and zoogeographical processes taken during the 

 speciation process for the various cutthroat trout subspecies may not be known for quite some 

 time, if ever. Numerous theories and much speculation have been tendered (Behnke 1992, Smith 

 et al. 2002). More recent advances in genetic testing methodologies have offered new insight 

 into the pre-historical cutthroat trout story. This status update did not attempt to address the pre- 

 historical picture. Rather we intended to focus on a more recent historical point of reference as a 

 way of tracking changes that could be validated through written accounts and personal 

 observations. 



Historical habitats of YCT delineated by this assessment differ from previous assessments 

 (Henzel 1959; Behnke 1979; Hadley 1984; Behnke 1988; Varley and Gresswell 1988; Thurow et 

 al. 1988; Behnke 1992; Gresswell 1995) for a number of reasons. A notable difference is the 

 reference period of historical occupancy. Behnke (1979; 1992) indicated that the western extent 

 of YCT range likely extended to portions of the Snake River, near the Idaho-Washington border. 

 The type locality for the name bouvieri was Waha Lake in western Idaho. Behnke (1979 and 

 1992) states that S.c. bouvieri were the original native trout of the entire Snake River some time 

 prior to the last glacial period (8,000 to 12,000 year ago) and replaced by redband and westslope 

 cutthroat trout below Shoshone Falls after that time period. Behnke (1979; 1992) notes that all 

 tributaries between Palisades Reservior and Shoshone Falls have S.c. bouvieri as the native trout. 

 Expansion into the Yellowstone River basin is felt to be via a connection between Pacific Creek 

 in the Snake River basin and Atlantic Creek which is a Yellowstone River tributary (Behnke 

 1992). Behnke (1979 and 1992) discussed eastern expansion within the Yellowstone River basin 

 and concluded that YCT occupied the mainstem Yellowstone River and tributaries as far as the 

 Tongue River. This eastern expansion would have occurred during the last 8,000 years. Many 

 status reports (Hadley 1984; Varley and Gresswell 1988; Gresswell 1995) cite Behnke (1979 and 

 1992) as the reference source for historical distribution of YCT there by anchoring to a time 

 period with a pre-historical perspective. A recent status review (May 1996) discussed the 

 historical range from a more immediate perspective using European exploration of the inland 

 portion of west (circa 1 800) as a historical benchmark. While it is reasonable to assume that the 

 pre-historical distribution of YCT likely expanded and contracted over time as environmental 

 and climatic conditions changed, written documentation that provides a more comparative 

 reference to current conditions began around 1 800. Kruse et al. (2000) completed a recent status 



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