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Climate change may be impacting wolverines in North America, but federal officials have decided that's not enough to warrant protection under the Endangered Species Act.

Dan Ashe, director of the U.S. Fish and Wildlife Service (FWS), announced Tuesday that his agency was withdrawing its proposal to list the wolverine as a threatened species. But he added the agency is not ignoring the real threat of climate change to North American wildlife.

"We consider climate change among the most significant conservation challenges of our time," he said. "The data sets show it is happening and will increase disruptions to the living support systems of both people and wildlife."

The decision to withdraw the proposal for wolverines has been "complex and challenging," he said, "but we believe it is the right decision given the information available to us today. In this case, we simply do not know enough about the ecology of the wolverine and when or how it will be affected by a changing climate to conclude...that it is likely to be in danger of extinction within the foreseeable future."

The decision to list the polar bear in 2008 was based on climate change issues, which have been considered in discussions about other species as well, Ashe said, such as the pika. The agency decided a pika listing was not warranted in 2010.

The initial proposal for a wolverine listing came from FWS biologists in Montana under the theory that loss of spring snow due to climate change would hinder wolverine denning and reproduction. The far-ranging animals seek alpine environments where temperatures are cold year-round and snow cover persists through May.

While wolverines have been spotted in Utah — including one photographed by a trail camera in the Uinta Mountains in February — it's unclear whether any have settled in the state.

Critics of the decision against listing wolverines say even without threats from climate change, the low population — estimated between 250 and 300 by FWS — warrants federal protection.

"The Service is ignoring the numerous serious threats to wolverines, including the species' low genetic diversity and impacts such as trapping and winter recreation," said Jamie Rappaport Clark, president and CEO of the Defenders of Wildlife, in a statement.

Only a few dozen females are able to produce offspring in any year, Clark noted. "Are we really willing to deny any sort of federal protection for a species whose low numbers make it one of the rarest in the continental U.S.?"

The Western Association of Fish and Wildlife Agencies, while meeting in Salt Lake City last fall, crafted a request to delay a listing decision. State biologists cited what is believed to be an historic high population of wolverines since European settlement, and their belief that climate change models were not a reason to list species under the act.

Bill Bates, wildlife section chief for the Utah Division of Wildlife Resources (DWR) said he was glad to hear of the agency's decision against listing.

"We brought up issues during meetings here in Salt Lake and we appreciate them being able to take a look at those points and reevaluate their decision," Bates said. "We appreciate the fact they are willing to put trust in the states and allow us to manage wolverines."

The question for Utah is whether the state has sufficient habitat for a reproducing population, he said.

"This [decision] is actually really exciting for us," Bates said. "It allows us to look more in depth what might be out there and allows us to begin the process of a management plan."

Bates encourages people who believe they have seen a wolverine to share their sighting with DWR.

The federal agency's decision was foreshadowed last month when the Center for Biological Diversity released a memo it had acquired, written by Noreen Walsh, regional director for the agency's Mountain-Prairie Region, to the wolverine team. Walsh said the impacts of climate change on wolverines were unclear and that she was recommending a withdrawal of the listing proposal.

Ashe said it was not uncommon for the service to change course and that the biologists who made the initial proposal understood the final decision.

"The eyes of many biologists have touched this issue. It is not unusual to come to a different conclusion," Ashe said. "She wrote a message to her field biologists sharing her rationale for a different conclusion."

Ashe said he asked the biologists whether they believed Walsh's conclusion was a reasonable interpretation of the facts or felt it was driven by some other motivation.

"Both said it was a different interpretation of the available scientific observations," Ashe said.

Ashe said his agency will continue to monitor the species and will consider any new information that might warrant federal protection.

Twitter: @BrettPrettyman