Yellowstone National Park has started capturing bison migrating outside the park and will hold them in pens for possible slaughter as part of a population reduction program, officials said Monday. The annual operation began Sunday and by mid-day Monday six bison had been captured as they entered the Gardiner Basin along the Yellowstone-Montana border, park spokeswoman Linda Veress said.

State and federal officials want to reduce Yellowstone's bison herds by up to 900 animals this winter under an agreement aimed at shielding Montana's cattle industry from the disease brucellosis, which many bison carry.

Bison in Yellowstone National Park. CBS

The park has about 4,900 bison. When that population expands more animals take part in the winter migration, in which bison journey to lower elevations in Montana in search of food.

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The population reduction would come through a combination of hunting, slaughter and placing up to 110 animals into quarantine for potential relocation at a later date.

As CBS "Sunday Morning" contributing videographer Judy Lehmberg reported in January, Yellowstone managers have tried to deal with the large bison population for years, while at the same time attempting to appease both those who don't want any bison killed, and the hunters, ranchers and some locals who want the population controlled.

For years Montana Indian tribes have been requesting "surplus" bison from Yellowstone to repopulate their reservations. Their request was finally partially granted last February, when 55 male bison were transported to Fort Peck Indian Reservation in central Montana, where a fenced area has been designated for them.