FLAGSTAFF, Ariz. — The National Park Service plans to thin a herd of bison in the Grand Canyon through roundups and by seeking volunteers who are physically fit and proficient with a gun to kill the animals that increasingly are damaging park resources.

Some bison would be shipped out of the area and others legally hunted on the adjacent forest. Within the Grand Canyon, shooters would be selected through a lottery to help bring the number of bison roaming the far northern reaches of the park to no more than 200 within three to five years.

Some 600 of the animals now live in the region, and biologists say the bison numbers could hit 1,500 within 10 years if left uncontrolled.

The Grand Canyon is still working out details of the volunteer effort, but it’s taking cues from national parks in Colorado, the Dakotas and Wyoming that have used shooters to cut overabundant or diseased populations of elk. The Park Service gave final approval to the bison reduction plan this month.

Sandy Bahr of the Sierra Club says she’s hopeful Grand Canyon will focus mostly on non-lethal removal.