NEPA--Environmental Assessment

Silverton Grazing Risk Assessment
popular summer recreation trail and is the main access route for hikers and horseback
riders into the central Weminuche Wilderness and the Pine River basin. Re-opening the
Pine-Piedra Stock Driveway for use by sheep would require a significant amount of
mechanical work, including moving large amounts of downed logs that were placed across
the trail as fireline mitigation after the 2002 Missionary Ridge wildfire.
To prevent having to trail domestic sheep up the Pine River trail and through the heart of
the S28 Vallecito Creek bighorn sheep herd’s summer range and summer concentration
area, or up the lengthy Pine Piedra Stock Driveway, it was proposed to access the Pine
River Allotment from the north via Rio Grande Reservoir. The proposal was to truck
domestic sheep to Rio Grande Reservoir, then trail sheep up the Weminuche Trail, south
over Weminuche Pass, and into Rincon La Vaca and Rincon La Osa. Sheep would then be
trailed back out via the Pine River Trail, over Weminuche Pass and back down to Rio
Grande Reservoir. We were unable to obtain permission from the Rio Grande National
Forest to use this access route. This route would take sheep through and very close to
mapped summer range for the S16 Cimmarona/Hossick herd.
If the Pine River Allotment were to be restocked with domestic sheep, potential for contact
with bighorn sheep from the S16 Cimmarona/Hossick herd and the S28 Vallecito Creek
herd appears to be high. Moving domestic sheep from a “High Risk” allotment in the
Silverton Landscape to the upper Pine River Allotment would be moving sheep to an area
of equal or greater risk for contact with bighorn sheep, thereby maintaining the same
problem, just moving it to a different location. We recommend not stocking any portion of
the Pine River Allotment due to its lengthy wilderness access route, lack of permission for
access from Rio Grande Reservoir, substantial overlap with mapped summer range for the
S16 Cimmarona/Hossick bighorn sheep herd, and need to trail through mapped summer
range of the S28 Vallecito Creek bighorn sheep herd.
RISK ASSESSMENT PROCESS
This “Risk Assessment” process involved the participation by FS/BLM wildlife biologists,
FS/BLM rangeland management specialists, FS/BLM decision makers, Colorado Division
of Wildlife terrestrial biologists and District Wildlife Managers, and domestic livestock
permittees. A series of meetings were held to review maps of the affected bighorn sheep
herds and grazing allotments.
The focus of the risk assessment process was on active and vacant domestic sheep
allotments (see Figures 2 and 3, below). Because vacant allotments could be restocked
administratively at any time, it is important to provide a risk rating in the event the
allotment was to be restocked. Allotments that have already been closed were not
specifically reviewed but would have received a rating of low risk.
The risk of physical contact between domestic sheep and bighorn sheep, with the
potential for subsequent disease transmission, was given a rating of “High’, “Moderate”, or
“Low”. Disease transmission however, is considered a correlate of contact, not an effect.
And, although disease transmission is discussed in this assessment, these ratings are not
intended to be an estimate of disease transmission probability, only an estimate of
relative level of risk for physical contact between domestic and bighorn sheep.
A risk rating of “High” indicates that contact between domestic sheep and bighorn sheep
is thought to be likely in the immediate future, although disease transmission resulting in
a bighorn sheep mortality event is by no means certain. If allotments have been operated
for many years without apparent disease transmission, we do not use this observation to
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