For a quick estimate, convert the forage assigned to livestock (AUMs) to wild horses and add the result to the AML.
The HMA boundary coincides roughly with the boundary of the Rim Pasture Allotment, as shown in the Western Watersheds map. (Click on image to open in new tab.)
The 86 horses allowed by plan consume 1,032 AUMs per year. The HMA covers 24,584 total acres, including 19,085 BLM (public) acres.
The five permittees receive 3,976 AUMs per year according to Table 2.
The Allotment Master Report is not working today but the Allotment Information Report, also at RAS, indicates a forage allocation of 3,982 AUMs per year at Rim Pasture. The allotment is in the Improve category according to the AIR and contains 19,100 public acres.
The forage assigned to livestock, based on data in the EA, would support an additional 3,976 ÷ 12 = 331 wild horses, for a True AML of 86 + 331 = 417. This is the number of animals the HMA could support if it was managed principally for wild horses, as specified in the original statute.
The current population of 179 is well within this range, so there are no excess horses in the HMA and there is no need for a roundup or fertility control program.
The 331 horses displaced from the HMA by permitted grazing represent about 0.7% of the 50,000 animals in off-range holding.
The current AML corresponds to about 21% of the total authorized forage, neglecting wildlife, meaning the HMA is managed primarily for livestock.
Forage availability in this area is very high, 262 AUMs per year per thousand acres, which would support a stocking rate of almost 22 wild horses per thousand acres!
The target rate across all HMAs is one wild horse per thousand acres.
AMLs and stocking rates are low relative to the available resources because the bureaucrats put ranching interests far above those of the horses.
Would an HMAP fix that? Nope.
UPDATE: AMR has been fixed, report for Rim Pasture posted.