The management plan assigns 363 × 12 = 4,356 AUMs per year to the horses at the upper end of the AML.
The Draft EA for resource enforcement actions in the HMA provides data for livestock grazing in Table 2.1. Additional information was obtained from the Allotment Master report in RAS.
Livestock receive 19,758 AUMs per year per Table 2.1. The total authorized forage inside the HMA is 4,356 + 19,758 = 24,114 AUMs per year, neglecting wildlife.
That means the horses can consume up to 18% of the authorized forage, sometimes referred to as ‘their food.’
The proposed action will gather the HMA to the lower end of the AML, leaving around 163 horses. Growth of the herd will be minimized with contraceptives.
The remaining horses will require 163 × 12 = 1,956 AUMs per year, just eight percent of the authorized forage, on land set aside for them.
AUM curtailments, if any, can be relaxed after the roundup, as forage consumed by ‘excess’ horses shifts back to the ranchers. This ‘thriving ecological balance’ should prevail for many years, thanks to the fertility control program and its adherents.
The forage assigned to livestock would support an additional 1,645 wild horses, for a True AML of 363 + 1,645 = 2,008.
The current population of 828 is well within this range.
If the HMA was managed principally for wild horses, per the original statute, there would be no need for a roundup and fertility control program.
RELATED: Comments Invited on Draft EA for Sand Wash Gather Plan.
Western Horse Watchers Association 
As a visitor to SWB and knowing many of the volunteers. Sheep about 5000 go through the basin twice a year. I can’t tell you exact time maybe a week to two weeks. Otherwise no other ranchers use the basin. It is horses and wildlife only.
I’m writing a letter at this very moment!!
It is time to look at allowed numbers of wild horses in HMAs/HAs in terms of science and not in terms of politics as suggested by the NAS. It is time to evaluate critical habitat resources needed and to secure, develop, and maintain them. Follow the 1971 Wild-Free Roaming Horse and Burro Act which says the DOI Secr. is to manage these animals to achieve a “THRIVING,natural, ecological BALANCE. The horses are to be “where found”, their areas
where found are to be used “principally” but not “exclusively” for their welfare needs, and scientists, such as biologists, geneticists, ecologists are to be used to accomplish this task. Public land ranchers and herbivore hunters and trappers should not be calling the shots.