For the second time this year, vandals have freed dozens of Yellowstone National Park bison being held in quarantine, with some possibly heading to slaughter.

Most of the 73 bison freed when the pen's fencing was cut open sometime between 9 pm. Wednesday and 6 a.m. Thursday stayed in the vicinity of the park's Stephens Creek holding pens, according to a park release.

Ninety-six park bison had been captured in the past week and corralled at Stephens Creek to be tested for brucellosis, a disease that can cause bison, cattle, and elk to abort their fetuses. Some would have been held for possible quarantine, while others would have been transferred to Native American tribes and shipped to slaughter, according to park officials.

"This act of sabotage, along with the incident that occurred on January 16, is a setback for bison conservation," said Yellowstone Superintendent Dan Wenk. "Creating a successful quarantine program will allow the transfer of live animals to tribes to develop conservation herds on tribal lands. The saboteurs are only ensuring more bison will be shipped to slaughter." 

On January 16, park staff discovered that more than 50 bison that were being held for possible transfer to the Fort Peck Indian Reservation were illegally freed by someone. 

The animals were being held and tested for brucellosis at Stephens Creek as part of a plan being considered to establish a quarantine program at the Fort Peck Indian Reservation in central Montana.

The purpose of that program would be to augment or establish new conservation and cultural herds of disease-free plains bison, enhance cultural and nutritional opportunities for Native Americans, reduce the shipment of Yellowstone bison to meat processing facilities, and conserve a viable, wild population of Yellowstone bison. 

According to Yellowstone staff:

• Operations at the Stephens Creek facility are taken in support of the Interagency Bison Management Plan (IBMP) goal to reduce the population this winter. Partners are aiming to cull 600-900 animals through a combination of shipping and the public and tribal hunt. 
• On January 4, 2018, the IBMP partners agreed to a 2018 winter operations plan that calls for a reduction of Yellowstone’s current population of 4,800 bison because the state of Montana has limited tolerance for natural bison migrations from the park onto state lands. 
• Bison capture and shipping operations may continue through March.
• Information about the number of animals that are captured, processed, shipped, and hunted will be provided every other week in the Bison Operations Updates of the IBMP website. 
• Learn about the annual bison migration from senior bison biologist Rick Wallen in a Facebook Live interview.  
• For more information about bison management, visit https://www.nps.gov/yell/learn/management/bison-manage