Tributary AssessmentExecutive Summary Trout population monitoring by the Idaho Department of Fish and Game (IDFG) indicated a 95% decline in the native Yellowstone cutthroat trout (YCT) population in the Teton River from 1999 to 2003 (Shrader et al. 2003). In response to this substantial decline in the native fishery, Friends of the Teton River combined resources with numerous state, federal, and private agencies in order to develop a watershed-wide assessment of the YCT population remaining in the mountain portions of all significant Teton River tributaries. The ‘Teton Headwaters Cutthroat Trout Population Assessment’ survey was implemented during the summer of 2005 to quantify trout populations and species composition in the mountain sections of 15 Teton River tributaries. The survey was conducted on United States Forest Service (USFS) land. One hundred meter long sample sites were placed every two kilometers, spanning from the USFS boundary upstream to the upper extent of flowing water on all significant tributaries in all selected drainages. Single-pass and multi-pass depletion electro-fishing methodologies were utilized in order to quantitatively assess trout populations, densities, and species compositions. Habitat characteristics, including stream geometry, substrate characteristics, bank conditions, large woody debris (LWD) abundance, and riparian vegetation types were also assessed. The results of this study provide an inventory of trout populations, trout densities, and species compositions, and species ranges in all Teton River tributaries, and a large-scale assessment of riparian habitat throughout the region’s USFS land. Four drainages, Bitch Creek, Badger Creek, South Leigh Creek, and Darby Creek, were found to contain only Yellowstone cutthroat trout (YCT). The lack of Eastern brook trout (EBT) invasion in these drainages can be explained by the characteristics of these tributaries’ connectivity to the Teton River, and the fact that the Teton River becomes too large to sustain EBT before it meets Bitch and Badger creeks. Additionally the unaltered hydrology of Bitch Creek favors YCT, and likely prevents rainbow trout (RBT) invasion of the system (Van Kirk, 2005). South Leigh and Darby Creeks have not been invaded by EBT, probably because they are seasonally dewatered for irrigation for a substantially long distance and time, respectively. Eight drainages, North Leigh, Teton, Moose, Trail, Little Pine, Mahogany, Horseshoe, and Packsaddle Creeks, were found to contain populations of both YCT and EBT. In all of these drainages, EBT dominate the system in terms of species composition, population size, and species range. A comparison of this survey’s results with a 1998 survey reveals that the YCT percentage of the total trout population in five of these tributaries has declined.
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