NEPA--Environmental Assessment

Silverton Grazing Risk Assessment
infer a lower risk rating. The fact that contact has not been observed, or a bighorn disease
event has not been detected, does not imply a lower risk for such events happening in the
future. For this reason, the allotment would still receive a rating of “High Risk”. A rating
of “Moderate Risk” indicates that physical contact between bighorn and domestic sheep
may occur at some point in the future, but effective separation may be achieved and/or
maintained for many years. The risk of physical contact between bighorn and domestic
sheep, with the subsequent potential for a bighorn disease outbreak, is thought to be
substantially less than for allotments in the “High Risk” category. Factors that reduce the
apparent risk of contact could include: application of herding techniques, bighorn sheep
distribution patterns, presence of towns, presence of habitat features that act as barriers
to bighorn sheep movement (Schommer and Woolever 2001). A rating of “Low Risk”
indicates that physical contact between domestic and bighorn sheep is believed to be
unlikely or irregular and unpredictable with the subsequent potential for a bighorn
disease outbreak thought to be unlikely or unpredictable in the future under the current
circumstances.
Where overlap exists between active domestic sheep allotments and mapped bighorn
sheep summer range or summer concentration areas (see Figures 1 and 2, below), the
risk of contact between domestic sheep and bighorn sheep, with the potential for
subsequent disease transmission, is “High” (see Figures 3 and 4, below). In vacant
allotments, the risk of contact is “Low” when the allotment is vacant, but becomes “High”
when the allotment is restocked.
Where overlap exists between active domestic sheep allotments and mapped bighorn
sheep summer range but domestic sheep are not actively grazed in that portion of the
allotment, the risk of contact between domestic sheep and bighorn sheep, with the
potential for subsequent disease transmission, may be either “High” or “Moderate”,
depending on the circumstances. The risk level assigned to the allotment depends on
whether or not there are mitigating factors such as distance to actively grazed portions of
the allotment, terrain features providing separation, presence of broad bands of dense
forest or presence of towns providing barriers to bighorn sheep movement, etc.
A risk rating of “High” could be mitigated down to a rating of “Moderate” with the
application of design criteria, changes in domestic sheep herding practices, not grazing
certain portions of the allotment, application of design criteria designed to reduce the
potential for contact, etc.
After assigning an initial risk rating, additional factors from the list provided below were
considered and a determination was made whether to change the initial risk rating.
Factors such as the application of project design criteria differ between Alternative 2 and
Alternative 3, leading to potentially different risk ratings for the same allotment among
the two alternatives.
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