YCT Multi-state Assessment February 10, 2003 



Results 



Historical Range 



Based on the LLID hydrography layer, a total of about 17,407 miles of lotic habitat were 

 identified as having been historically (circa 1800) occupied by YCT (Figure 1; Appendix E). 

 The estimated amount of historical range in each state was about 4,049 miles in Montana (23%), 

 6,269 miles in Idaho (36%), 6,889 miles in Wyoming (40%), and nearly 100 miles (0.5%) in 

 both Nevada and Utah. Historically occupied habitat included stream segments occupied by both 

 large and fine-spotted forms of YCT, and in some instances both forms were present. We 

 believe that fine spotted YCT occupied only those HUC's (i.e. Snake Headwaters, Gros Ventre, 

 Greys-Hoback, Salt and Palisades) in the upper most portion of the Snake River basin. In some 

 instances, it was probable that both forms were present together in the same stream segments 

 within the upper Snake River basin. 



Several 4'*' code river basins, including the Lower Rosebud, Lower Tongue, Dry Creek, 

 Badwater, and Muskrat in the Yellowstone River system, and the western-most watersheds in the 

 sinks drainages in the Snake River system were excluded as historical habitats, even though 

 previous assessments may have included some or parts of these basins within the historical 

 range. We excluded these watersheds as historically occupied because YCT were not found 

 during fishery surveys, either in historical or current records, in any waters within these basins; 

 and/or we found written historical accounts that specifically stated that streams within the basin 

 were devoid of trout. 



Current Distribution 



YCT currently occupy about 7,528 miles (43%) of the nearly 17,400 miles of historically 

 occupied habitats. YCT currently occupy over 2,100 miles in Idaho (35% of historical), over 

 1,400 miles in Montana (35% of historical), about 3,860 miles in Wyoming (55% of historical), 

 just over 40 miles in Nevada (45% of historical), and about 42 miles in Utah (41% of historical). 



As part of the current distribution assessment an attempt was made to identify, on a stream 

 segment basis, the presence or absence of the two forms of YCT (i.e. large spotted and fine 

 spotted YCT). For each stream segment, reviewers were asked to identify which YCT form was 

 dominant. In addition, many reviewers made comments suggesfing that both spotting forms 

 were present. The large spotted form of YCT were identified as being present in 6,091 miles 

 (81% of current) of the 7,528 miles of currently occupied habitat. Of these stream miles, large 

 spotted YCT were sympatric with fine spotted YCT in 1,084 miles, either as the dominant form 

 (544 miles; 7.2%) or as the sub-dominant form (540 miles, 7.2%). Fine-spotted YCT were 

 identified as being the only spotting form in 1 ,438 miles of stream. Due to the use of the fine- 

 spotted form in recreational fishery management, their distribution has been enlarged to include 

 portions of 15 HUC's with total occupied habitat estimated at 2,522 miles (34% of current). 

 There were no HUC's that contained only fine-spotted YCT. 



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