There are many factors that are currently leading to a decline in the number of wild B. grunniens, which is currently estimated at around 15,000. Perhaps one of the largest has been hunting by humans. According to Schaller and Wulin (1995), while the Tibet Forest Bureau is making substantial efforts to protect yak (including fines of up to $600), "Hunting is difficult to suppress without a mobile patrol force, as the recent decimation of wildlife in the Arjin Shan Reserve has shown."
Also, as pastoralists are starting to change their habits from a nomadic to sedentary lifestyle their habit is beginning to become fenced off. The introduction of domesticated yaks (via the pastoralists) also presents problems in regards to the transmission of disease (e.g. brucellosis), and possible increased competition for the same grazing land (Schaller & Wulin, 1995).
Domesticated yak are not listed as endangered due to their large numbers.
US Federal List: endangered
CITES: appendix i; no special status