BOZEMAN - Nearly 50 more bison from Yellowstone National Park were sent to slaughter Friday, bringing to 347 the number shipped off since roundup efforts began, a park spokesman said.

In the past week and a half, authorities have captured 651 bison for venturing too near or beyond Yellowstone's northern border.

Of that number, 347 have been sent to slaughter, 38 calves have been sent to a quarantine facility and 264 remain at the Stephen's Creek capture site just inside the park's northern boundary.

Park spokesman Al Nash said most of the bison appear to be coming from the central herd, which has a home turf in the Hayden and Firehole River valleys.

A state-federal management plan allows for the hazing and capture of bison from Yellowstone in an effort to reduce the possible spread of brucellosis from bison to cattle in Montana. When the overall bison population exceeds 3,000 animals, park officials can send captured animals to slaughter without testing for brucellosis.

The bison population was estimated at 4,900 before capture operations began.

Nash stressed the operations were not a form of population control, but bison advocates said they don't buy that position.

"I don't see where they're doing much other than population control," said Mike Mease, one of the founders of the Buffalo Field Campaign.

Brucellosis is a problem, he said, "but this is not the solution. We're not gaining any knowledge."

Nash has acknowledged the efforts will have an effect on the Yellowstone bison population, but said officials are confident the population will still be well over 3,000 animals in a late winter-early spring count. A state-federal management plan lists 3,000 as a target population.