YCT Multi-state Assessment February 10, 2003 



assessment of YCT in specific drainages of the Bighorn River and primarily anchored to the 

 more recent time period (May 1996) as a historical reference period. 



Another significant difference between this status assessment and many of the previous 

 assessments is associated with the base representation of occupied habitat across the potential 

 range. Behnke (1979, 1988 and 1992) used narratives and qualitative maps to describe the outer 

 most boundaries of YCT historical range. These publications made reference, from field notes 

 and observations, to specific streams but did not attempt to provide quantification of the amount 

 of historically occupied habitat. Hadley 1984 provided a very limited qualitafive reference to 

 historical occupancy by stating: "The Yellowstone cutthroat trout in Montana was at one time 

 abundant in most waters in the Yellowstone River basin from the Montana- Wyoming border to 

 the Tongue River system." Varley and Gresswell (1988) cited Behnke's publications relafive to 

 historic range and then provided further quantitative detail. They mention that original habitat 

 was comprised of 44,500 ha of lake habitat and 24,000 km (15,000 miles) of sfream 

 environment. Varley and Gresswell (1988) did not provide an explanafion on how they obtained 

 these historical estimates. Kruse (2000) in turn cited Varley and Gresswell (1988) when 

 commenting on the historical distribution. In the USDA Forest Service conservadon assessment 

 for the inland cutthroat frout subspecies (May 1996) an attempt was made to quanfify YCT 

 historical range based on mapped stream miles within the geographical area believed to have 

 been occupied in about 1800. 



The generalized boundaries depicted in most assessments (e.g. Behnke 1979 and 1992) 

 encompassed many 4"' code HUC's that we excluded (e.g. lower Tongue River, lower Rosebud 

 within the Tongue River basin; Badwater, Muskrat, and Lower Bighorn in the Bighorn River 

 basin; and, several watersheds on the north side of the mainstem lower Yellowstone River) based 

 on a focused review by individuals knowledgeable about the specific geographical areas 

 reviewed. In addition, the lack of historical quantification and site specificity in most status 

 discussions can imply to many readers that all or most streams within the generalized boundaries 

 depicted were occupied by YCT. 



Our estimates suggest approximately 17,400 miles , located within 39 4"^ code HUC's, were 

 occupied by YCT at the time of Lewis and Clark's "Corps of Discovery" expedition. This 

 amount of historically occupied habitat is in contrast to the nearly 32,200 miles of stream 

 contained in the 1 : 100,000 hydrography associated with these watersheds. Nearly 14,600 miles 

 of streams were excluded from being historically occupied due to passage barriers (e.g. physical, 

 temperature, etc.) and inadequate habitat (e.g. minimal flows, excessive gradients, intermittent or 

 ephemeral flows, etc.). Some stream reaches were excluded because of historical references and 

 other antidotal observafions indicating that the stream was barren offish (i.e. Jordan 1891). 

 Habitats were included on the basis of historical journal entries, scientific reports, anecdotal 

 information on presence, evidence of basin transfers and presence of frout when no barriers were 

 present. 



May (1996) reported that YCT historically occupied just over 16,600 miles of riverine habitat. 

 Of that total, Wyoming had 10,949 miles (66%), Idaho had 3,587 miles (22%), Montana 

 contained just over 1,920 miles (12%) and 210 miles (1%) were attributed to occupied habitats in 

 Utali and Nevada combined. We estimated that about 1 7.400 miles of habitat were historically 



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