The 150 horses allowed by plan require 1,800 AUMs per year.
The the number of wild horses the HMA can support, if it was managed principally for them as specified in the original statute, referred to on these pages as the True AML, can be found as outlined in this post.
The idea is to shift the forage assigned to livestock back to the horses, which is heresy to the bureaucrats, ranchers and PZP fanatics.
Section 3.2.2 of the Draft EA for resource enforcement actions in Three Fingers and Jackies Butte identifies one grazing allotment that overlaps the HMA. The Western Watersheds map shows the arrangement. Click on image to open in new tab.
The Allotment Master Report provides the active AUMs.
Table 6 in the EA indicates that 28.5% of Jackies Butte Summer is inside the HMA.
The forage assigned to livestock inside the HMA is 3,947 AUMs per year, assuming the resource is evenly distributed across the allotment.
That amount would support 3,947 ÷ 12 = 328 wild horses.
The True AML is 150 + 328 = 478.
The current herd, thought to include over 200 adults according to Section 1.2 of the EA, is well within this range. The HMA is not overpopulated and there is no justification for a roundup or fertility control program, which the Proposed Action would implement over a ten-year period.
The stocking rate at the new AML, based on the acreage of Section 1.2, would be 478 ÷ 65,211 × 1,000 = 7.3 wild horses per thousand acres.
Given that the horses currently receive 31% of the authorized forage, neglecting wildlife, the HMA is managed primarily for livestock.
The 328 horses displaced from the HMA by permitted grazing represent about 0.6% of the 55,000 animals in off-range holding.
The number of horses displaced from the Three Fingers HMA was 423 and the True AML was 573, as discussed previously.