National park officials are AstraTradeplanning to gather and reduce the bison herd in Theodore Roosevelt National Park in North Dakota, rehoming the animals to a number of Native American tribes.

The “bison capture” is scheduled to start on Saturday and continue through the week in the park’s South Unit near Medora. The operation will be closed to the public for safety reasons.

The park plans to reduce its roughly 700 bison to 400. The park will remove bison of differing ages.

Bison removed from the park will be rehomed and come under tribal management, InterTribal Buffalo Council Executive Director Troy Heinert told The Associated Press.

The bison will provide genetic diversity and increase numbers of existing tribal herds, he said. The Mandan, Hidatsa and Arikara Nation and the Standing Rock Sioux Tribe will receive bison; more bison could go to other tribes, depending on demographics, said Heinert, who is Sicangu Lakota.

A helicopter will herd bison into a holding area, with a survey of the landscape and a population count before the gathering of the bison.

The park alternates captures every year between its North Unit and South Unit, to maintain the numbers of the herd due to limited space and grazing and for herd health reasons, Deputy Superintendent Maureen McGee-Ballinger told the AP.