NEPA--Environmental Assessment
NEPA--Environmental Assessment
NEPA--Environmental Assessment
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Silverton Grazing Risk <strong>Assessment</strong><br />
The current San Juan National Forest Land and Resource Management Plan of 1983<br />
(Forest Plan), amended in 1992, and the BLM’s San Juan/San Miguel Resource<br />
Management Plan of 1984 (RMP), along with Allotment Management Plans (AMP) and<br />
Grazing Permits, regulate the current numbers and type of livestock, dates of use,<br />
salting, vegetation manipulation and other activities undertaken for the purpose of<br />
grazing domestic livestock on public lands.<br />
Domestic Sheep are the only livestock permitted to graze in this landscape, and their<br />
principle forage areas are in the alpine zone. Alpine rangelands have been used for<br />
grazing domestic sheep in this Landscape since the late 1800’s. Prior to government<br />
control, sheep were herded in tightly grouped bands and continuously bedded in the<br />
same location for several nights in a row, which resulted in large forage losses and soil<br />
damage from trampling and excessive trailing. Some sites in the Silverton Landscape still<br />
display these historic effects. There are no additional bands of domestic sheep being<br />
grazed on adjacent or intermingled non-federal lands, in addition to the bands permitted<br />
to graze on the Federal allotments under analysis in this document.<br />
Rocky Mountain bighorn sheep are native to the Silverton Landscape. Desert bighorn<br />
sheep are not known or thought likely to occur in the Landscape. For this reason, this<br />
analysis refers only to Rocky Mountain bighorn sheep.<br />
One of the primary management concerns associated with domestic sheep grazing in the<br />
Silverton Landscape is the potential for physical contact between domestic sheep and<br />
bighorn sheep. This contact increases risk of subsequent bighorn sheep mortality events<br />
and reduced recruitment, primarily due to respiratory diseases (Western Association of<br />
Fish and Wildlife Agencies 2007). The complete range of mechanisms and/or causal<br />
agents that lead to disease events in bighorn sheep is still under debate, and not all<br />
bighorn sheep disease events can be attributed to contact with domestic sheep (Colorado<br />
Division of Wildlife 2009, Aune et al. 1998, Onderka and Wishart 1984). However, when<br />
contact between wild sheep and domestic sheep and goats has been documented, the<br />
severity of the wild sheep die-off is typically more pronounced (Aune et al. 1998, Martin et<br />
al. 1996). For these reasons, it is prudent to implement management actions designed to<br />
reduce or eliminate the potential for contact between wild sheep and domestic sheep<br />
(Colorado Division of Wildlife 2009, Western Association of Fish and Wildlife Agencies<br />
2007).<br />
This “Risk <strong>Assessment</strong>” analysis is focused on the “risk of contact” between bighorn sheep<br />
and domestic sheep. No presumption is made that contact will lead to disease<br />
transmission or a subsequent bighorn sheep mortality event. However, the assumption is<br />
made that physical contact between bighorn sheep and domestic sheep results in an<br />
increased risk to bighorn sheep of disease transmission and therefore it is prudent to<br />
reduce the risk of contact and/or increase the distance and/or degree of effectiveness of<br />
separation between the two species (Colorado Division of Wildlife 2009, Western<br />
Association of Fish and Wildlife Agencies 2007, USDI Bureau of Land Management 1998).<br />
The goal of this “Risk <strong>Assessment</strong>” is to provide the decision maker with an objective<br />
evaluation of the risk of contact between bighorn sheep and domestic sheep in each active<br />
and each vacant domestic sheep grazing allotment in the Silverton Landscape. The<br />
decision maker will then use the results of this “Risk <strong>Assessment</strong>” as an important factor<br />
of consideration in their decision regarding domestic sheep grazing in the Silverton<br />
Landscape.<br />
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