Wolf numbers have plummeted at Yukon-Charley Rivers National Preserve in Alaska, where National Park Service officials attribute the steep decline to the state's desire to reduce predators to improve hunting.

The 2.5-million-acre preserve's annual winter census of wolves estimates that the predator's population has fallen by more than 50 percent from just last fall. The drop is substantially more than normal and coincides with predator control efforts by Alaska Department of Fish and Game conducted near the preserve, the Park Service said in a release.

"This fall-to-spring drop in the number of wolves which den or spend a portion of their lives in the national preserve appears to be the highest on record," the release added. "Based on 20 years of data for wolves that use Yukon-Charley Rivers, a typical drop over the winter is in the 11 percent to 37 percent range."

In November 2012, NPS biologists counted 80 wolves in nine packs; going into the spring pupping season, biologists could account for between 28 and 39 wolves in six packs, the Park Service reported.

This year's report is vastly different from the one issued a year ago, when biologists said the preserve's wolf populations were thriving, with at least 71 animals divided among nine packs.

According to the Park Service, hunting and trapping typically results in about a half-dozen or fewer wolf kills each fall and winter. The majority of wolves that were killed this past winter are believed to have been part of the Alaska Department of Fish and Game’s aerial predator control program outside and adjacent to the preserve.

“We’ve had no formal communication from the State of Alaska on results of their helicopter and fixed-wing predator control work in the Fortymile country,” said Yukon-Charley Rivers Superintendent Greg Dudgeon. “But through informal conversations we understand they were focusing efforts in the areas outside the preserve. The NPS role is to keep the preserve ecosystem, of which wolves are a part, functioning as naturally as possible.”

Yukon-Charley Rivers National Preserve was established by Congress in the 1980 Alaska National Interest Lands Conservation Act, in part to “maintain the environmental integrity of the entire Charley River Basin… in its undeveloped natural condition for public benefit and scientific study; to protect habitat for, and populations of, fish and wildlife, including… wolves.”

Park Service policies aim to maintain natural processes, wildlife abundance and diversity, natural wildlife behavior, and not reduce a native species for the benefit of a harvested species.

“We manage Yukon-Charley Rivers and other National Park Service areas in a manner that maintains the natural dynamics of a relatively undisturbed ecosystem,” said Deb Cooper, NPS associate regional director. “The State of Alaska has a very different mandate with goals to reduce wolf and bear populations in hopes of growing more caribou and moose for hunters. In places like Yukon-Charley Rivers, our two very different mandates bump into each other, and meeting the purposes of these differing frameworks is a challenge for both agencies.”

National Park Service managers will be closely watching this summer’s production of wolf pups and considering whether it will be necessary to impose a delay in the opening of the fall sport season for wolf hunting and trapping.

“Looking ahead, we’ll attempt to determine if this year’s decline in wolves has put us in a position of needing to take a necessary conservation action,” Superintendent Dudgeon said. “Our intent is to preserve the environmental integrity envisioned by Congress when it established the preserve. “

National Park Service researchers will also look at the preserve’s prey populations. The State of Alaska has reached its population objectives for two of three moose populations in the upper Yukon-Tanana Rivers area, as well as for the Fortymile Caribou Herd. A 2012 state research report, supported in part by the National Park Service, cautioned that signs of nutritional stress were being seen in the caribou herd, and signs of potential overgrazing have been observed in the herd’s core upland tundra range, which includes portions of Yukon-Charley Rivers National Preserve.

The Park Service did note that traditional hunting and trapping within the preserve are not in conflict with the NPS mandate of conserving natural processes and managing for natural abundance.

“Hunting and trapping are significant activities in Yukon-Charley Rivers, and an important part of our heritage,” Superintendent Dudgeon said. “Offering sport and subsistence hunting opportunities in a place that retains its essential natural character and the ecosystem benefits of natural predator-prey dynamics is part of our mission.

“Preserving those qualities - alongside traditional recreation and subsistence practices - was a mandate from Congress more than 30 years ago. We hope to continue working with the State of Alaska to find ways to meet our respective missions. The National Park Service will continue to manage this public land unit consistent with our Congressional mandates.”