watervulnerability

Helena National Forest Watershed Vulnerability Assessment, Northern Region (R1)
Water Resource Value: Westslope Cutthroat Trout Habitat
Sensitivity
Cutthroat trout habitat was assessed using the “Matrix of Pathways and Indicators” for bull trout fisheries
described above (Table 3) in combination with the cutthroat distribution information and professional
knowledge of the specific subwatersheds. The ratings of FA, FAR and FUR were given to those
watersheds with known populations of cutthroat trout. Of the 155 watersheds with some portion of their
area under forest management, 76 have known populations of cutthroat trout. Five of these have a rating
of FA, 19 are FAR, and 52 are FUR (Figure 4).
Exposure
Westslope cutthroat trout are closely associated with headwater habitats which are often more stable than
downstream reaches. Therefore, they may be less influenced by changes in large scale environmental
conditions (Copeland, 2011, Wenger 2011a). Cutthroat trouts have a strong negative response to brook
trout presence at the subwatershed scale (Wenger, 2011b). Brook trout are highly sensitive to increasing
temperature, so the cutthroat trout could have an indirect positive response to climate change (Wenger,
2011b). Most of the subwatersheds on the Helena National Forest have a population of invasive brook
trout, brown trout or both. Only 17 of the subwatersheds do not have known populations of these invasive
species (Figure 5). We analyzed the effects of average summer maximum temperature increase as a net
positive interaction with cutthroat trout due to the parameter’s negative interaction with the invasive
populations of brook trout (Wenger, 2011b).
Figure 4. Composite watershed sensitivity rating for Westslope cutthroat trout
55 Assessing the Vulnerability of Watersheds to Climate Change