Ranchers and wildlife officials will be allowed to kill wolves that are attacking livestock as the animals are reintroduced along the Western Slope, the U.S. Fish and Wildlife Service said Friday.

The decision came as the agency declared gray wolves an experimental population under 10(j) rule of the Endangered Species Act, allowing for flexible management strategies as Colorado begins its reintroduction by Dec. 31.

Lawmakers approved legislation this year that would have suspended wolf reintroduction in Colorado until the 10(j) designation was met, but Gov. Jared Polis vetoed the effort, saying it was “unnecessary and undermines the voters’ intent and the hard work” over the past three years by Colorado Parks and Wildlife officials and other stakeholders.

The state’s plan allows ranchers whose livestock are killed by wolves to be compensated up to $15,000 per animal. It outlines many nonlethal interventions to discourage wolves from killing livestock, but allows the killing of wolves caught in the act of attacking livestock or working dogs. Killing wolves that are killing livestock would violate the Endangered Species Act without the 10(j) rule.

The decision was announced three weeks ahead of schedule, Colorado Parks and Wildlife director Jeff Davis said.

“National Environmental Policy Act work typically takes two to three years and it was accomplished in a little over a year-and-a-half,” Davis said in a news release Friday. “CPW leadership is very thankful to the demonstrated commitment and partnership with the U.S. Fish and Wildlife Service.”

Colorado voters in 2020 narrowly approved the highly contentious statewide ballot initiative directing Colorado Parks and Wildlife to restore wolves in the state.

Not requiring livestock owners to use nonlethal, preventive methods before killing wolves “incentivizes poor husbandry and opens the door to chronic conflicts and associated killings of wolves,” conservation nonprofit Center for Biological Diversity said in a statement Friday. Preventive measures could include removing the carcasses of livestock that weren’t killed by wolves before wolves can start to scavenge.

“The state wolf plan and this new federal authorization will probably need to be revised before too long to truly protect both wolves and livestock by mandating nonlethal prevention,” senior conservation advocate Michael Robinson said.

The federal wildlife service said Colorado is on track in its plan to reintroduce wolves, confirming that gray wolves will begin to be released along the Western Slope this year.

The release in December will be the first phase, and if all goes according to plan, 30 to 50 gray wolves will be introduced west of the Continental Divide over the course of three to five years.

Wildlife officials hope to use gray wolves captured from different packs in the Northern Rockies or other sites in Oregon or Washington, according to Colorado Parks and Wildlife wolf restoration and management plan. The states are reluctant to help but CPW remains confident wolves will be available to be released in Colorado by the end of the year.

Idaho declined to give Colorado any of its wolves and wildlife officials in Washington are still considering whether they will help, Colorado Parks and Wildlife spokesman Joseph Livingston said Friday. Colorado has not reached a finalized agreement with Oregon or any other state.

CPW also reached out to the Nez Perce Tribe in north-central Idaho, Livingston said.

The state has proposed wintertime releases in two areas on the Western Slope: along Interstate 70 corridor between Glenwood Springs and Vail, and along the U.S. 50 corridor between Monarch Pass and Montrose. The first releases are planned for state or private land around the I-70 corridor.

Colorado finalized its plan to restore gray wolves in the state in May. A unanimous decision was reached by Colorado Parks and Wildlife commissioners after more than two years of planning and hundreds of hours of meetings across the state. The U.S. Fish and Wildlife Service said it reviewed more than 20,000 comments in developing its Environmental Impact Statement, which distinguishes Colorado’s wolves as a nonessential experimental population.