CASPER, Wyo. -- In the early 1990s, the Wyoming Range mule deer herd numbered more than 60,000 deer. By 1993, numbers crashed to around 25,000. This year there are 28,900, according to data from the Wyoming Game and Fish Department.
Wildlife officials would like the Wyoming Range herd to reach 50,000 deer. Goals for the Sublette herd are 32,000, even though it numbers about 20,600. The two herds run in tandem; the Sublette herd's range starting near Jackson and running south and the Wyoming Range starting near Big Piney and Marbleton before heading south.
Causes for the decline vary, and most experts point to a combination of many things, including energy development, harsh winters, poaching and highway deaths.
Here is a breakdown of several of the most talked about causes of mule deer decline.
Natural gas development has negatively impacted the mule deer herds, according to both officials with the Bureau of Land Management and QEP Resources Inc., one of the main drilling companies on the Pinedale Anticline.
"There's no way we can say we have not had an impact at all," said Kevin Williams, the QEP Pinedale district manager.
What people debate is how large of an impact and what can be done to lessen it.
Williams believes that his company is improving its practices and doing its best to prevent additional decline.
Several companies, including QEP, Shell and Ultra Petroleum, have drilled a total of 2,400 wells on the Pinedale Anticline since 2000. After a new record of decision was signed in 2008 allowing drilling during winter, 1,100 wells have gone in, according to Shane DeForest, Bureau of Reclamation field manager for the Pinedale office.
As part of that record of decision, gas companies agreed to a mule deer mitigation plan if number of deer in the Mesa population, a part of the Sublette herd, decreased more than 15 percent of the overall Sublette herd's decrease using the 2005-06 population estimates, DeForest said.
That happened in 2010, when numbers went from 2,856 to 2,318 on the Mesa and 27,254 to 26,162 in the Sublette herd, said Greg Noble, assistant BLM field manager for minerals and lands.
The first step in addressing the decline is to protect the flank areas from disturbance and work on habitat enhancements on the project area. The second step is to purchase conservation easements around the developed area to protect migration. The third and final step is to change drilling operations. DeForest said BLM, using mitigation office funds given by the gas companies and working with other organizations, began buying easements when the record of decision was signed. He is now in the process of working on habitat projects such as fertilizing key areas.
No percentage trigger signals when habitat improvements have not worked and drilling needs to be changed, DeForest said.
"Modifications of operations are the final step. It is implemented after we do the final things and we find it doesn't produce an adequate result," he said.
Steff Kessler, Wyoming program manager for the Wilderness Society, wonders how low numbers will have to be before winter drilling stops.
"I think people are almost resigning themselves to the fact that the BLM isn't going to react soon enough, and the herd will decline to nothing," she said.
"I haven't seen any inspiration for hope."
* Highway mortalities
Some years, cars and trucks kill more deer on the highway in the area between Big Piney and LaBarge than hunters, said Gary Fralick, a Wyoming Game and Fish regional wildlife biologist.
In 1997, more than 400 deer were killed by vehicles and trains in Nugget Canyon between Cokeville and Kemmerer. Many of the deer that spend the winter in the canyon migrate to summer ranges in Greys River and Salt River, where the legal harvest that year was between 200 and 300 deer, Fralick said.
In 2008, the Wyoming Department of Transportation paid for and completed six underpasses in Nugget Canyon and plans to build two overpasses and six underpasses by next fall near Daniel Junction.
Last winter hit mule deer in southwest Wyoming hard. The Sublette herd lost between 45 percent and 60 percent of its fawns. The Wyoming Range herd lost as much as 75 percent of its fawns. It was the worst loss recorded in the Wyoming Range herd since 1990, according to the Wyoming Game and Fish Department.