FLAGSTAFF, Ariz. — A bison herd that lives almost exclusively in the northern part of Grand Canyon National Park will not be targeted for a deadly removal this fall.

The park used trained volunteers selected in a highly competitive and controversial lottery last year to kill bison, part of a toolkit to reduce the size of the herd that trampled the grasslands and archaeological sites on the north rim of the canyon.

Introducing the sound of gunshots and having people near the bison was intended to push the huge animals back into the adjacent forest where they could legally be hunted. But the efforts had little effect.

“They just moved a bit from where the activity was happening, and sometimes they would come back the next day,” said Grand Canyon wildfire program manager Greg Holm.

New surveys also showed the herd is closer to the target of around 200, up from around 500 to 800 animals when the park approved a plan to rapidly reduce herd size. The park is currently working with other agencies and groups on a long-term management plan for bison, an animal declared a US national mammal in 2016 and featured on the National Park Service logo.

Hunts for hundreds of years and a genetic bottleneck have nearly left the animals that once numbered tens of millions extinct in the United States. .

Yellowstone, which spans 3,500 square miles in Wyoming, Montana and Idaho, is also developing a new management plan for the approximately 5,500 bison there. He works with Native American tribes, state agencies and other groups to find ways to reduce the number of bison sent to slaughter.

Theodore Roosevelt National Park in North Dakota routinely rounds up bison using helicopters and corrals, then transfers some of the animals to tribes, other states, and national parks. Without natural predators, bison herds can grow rapidly and deplete resources, according to the park.

The Grand Canyon herd has not always lived within the park boundaries, where they can be seen along the highway leading to the North Rim entrance. The bison are the descendants of those brought to Arizona in the 1900s as part of an experiment in interbreeding with cattle.

The animals increasingly recognized that they could be hunted in the adjacent state forest and sought refuge in the national park. Hunting is not permitted in national parks, but the agency has the power to kill animals that harm resources, using park staff or volunteers.

Most of the bison in the Grand Canyon were removed by rounding them up and transferring them to Native American tribes who attempted to reestablish herds on their land. A controversial pilot project last fall sought out trained volunteers to cull up to 12 of the animals.

More than 45,000 people applied for this chance. In the end, 10 were chosen and they were able to kill four bison. Although the animals are massive, they are quick and agile and can hide among thick stands of trees.

Grand Canyon officials say they won’t repeat the program this fall, but it won’t be ruled out as a tool in the future. Another corraling effort is planned.

The latest bison population estimate based on aerial surveys and tracking devices shows 216 bison on the vast Kaibab Plateau, according to Grand Canyon National Park. Agencies that manage land and wildlife in far northern Arizona and study bison movements are meeting in July to begin discussing the long-term plan.

Part of that discussion will include creating more gaps in state-sanctioned bison seasons outside of Grand Canyon National Park to see if bison will go out of bounds, said regional supervisor Larry Phoenix. of the Arizona Department of Game and Fisheries.

Meanwhile, the Game and Fisheries Department is seeking permission to improve fencing, cattle guards and water catchments to expand the range of another bison herd in the extreme northern Arizona. The state imported 15 yearling bison from a private nature preserve in Montana in late 2017 and said the herd now needed more room to grow.

Phoenix is ​​confident that these bison won’t follow the others into the Grand Canyon, largely because the animals don’t know the other herd exists.

Environmental groups are skeptical the fences may prevent them from straying and increase the overall bison population in the area where they have been difficult and expensive to control.

They are asking the US Forest Service to do a thorough review of the proposal that takes into account climate change and impacts on plants and animals like the scissor-toothed kangaroo rat.