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Wyoming Game and Fish Department reports steep drop in Sublette mule deer numbers

by Wyoming Livestock Roundup

Two zigzag lines on a simple chart display a grim story of the Sublette mule deer herd on the Pinedale Anticline. 

The chart is on the cover of December 2018’s mule deer monitoring report for the Pinedale Anticline Project Office shows precipitous drops last year.

One steep line is the 48-percent drop in Mesa mule deer and the other, a 28-percent decline in the overall Sublette herd numbers, including the Mesa, for 2017-18 within the Pinedale Anticline Project Area. The net decline – 20 percent overall.

These are the worst numbers reported by Wyoming Game and Fish Department (WGFD) since the Anticline’s monitoring program set its baseline winter counts in 2006-07.

Inside the numbers

WGFD Biologist Phil Damm, who works with the Bureau of Land Management (BLM) in the Pinedale Anticline Project Office (PAPO), presented “Mule Deer Monitoring in the Pinedale Anticline Project Area” to the board of directors at its Dec. 12 meeting in Cheyenne.

It was prepared for the PAPO and WGFD by Western Ecosystems Technology, Inc., which has monitored the Sublette herd on Bureau of Land Management’s extensive Anticline oil and gas development since 2001.

The 20-percent drop is well over the 15 percent trigger defined in the Anticline’s 2008 Record of Decision. The Record of Decision for the project is the foundation for how Sublette mule deer and other wildlife are managed in its development zones and sets out set guidelines for management, monitoring and mitigation.

The baseline numbers against which declines – and growth, which last happened in 2008 – were 2,846 mule deer on the Mesa and 24,165 deer in the entire Sublette herd unit. 

Last February, 1,495 mule deer were on the Mesa and 17,299 in the Sublette herd.

Mitigation matters

When an annual net decline crosses the 15-percent threshold, mitigation measures are required. 

WGFD plans long-term habitat projects, and these are undertaken by the PAPO team, employees, the public and interested groups. Many projects have multiple partners, according to Damm. On the Anticline, operators – mainly Ultra Resources – pay $7,500 “spud” fees to the PAPO for mitigation.

Mule deer declines were not unexpected, according to Caleb Hiner, BLM Pinedale Field Office manager.

“We did an Environmental Impact Statement back in 2008 and said in the Record of Decision (ROD) that there would be significant impacts for wildlife,” Hiner pointed out. “We were very clear that there would be impacts.”

In 2009-10, the net decline was 25 percent with 26,732 deer and the next year, 2010-11, it was 16 percent with 23,426 deer. 

“This is the third time they have hit the trigger,” Hiner said. “It’s important to point out it hasn’t been hit three years in a row.”

Active projects

Mitigation began in earnest back then, and new projects are approved annually by the PAPO board, which meets in May in Pinedale and “continues for the life of the Pinedale Anticline,” Hiner added. “BLM is committed to working with its partners on the Pinedale Anticline to find appropriate mitigations.”

Past habitat projects have not slowed the decline, though. 

“I don’t know how to gauge the effectiveness of mitigation,” Hiner said. “The mitigation we are doing is within the reference area. We don’t have a ‘control’ to measure effectiveness.”

WGFD has technology on its side, said Damm.

“One key method we use to ensure these projects have benefits to PAPO mule deer is analyzing mule deer GPS collar data to inform the most suitable locations for project work, places where we will get the most ‘bang for our buck,’ so to speak.”

WGFD and partners have many projects that improve off-site and onsite habitat, according to Damm.

“Thousands of acres of habitat projects and dozens of miles of fence modifications have been completed over the last 10 years,” he said. “New habitat projects for Sublette mule deer are developed on an annual basis and much work is yet to be initiated.”

Pace of drilling

A 2017 report showed mule deer avoid active oil and gasfield facilities.

Hiner said mule deer already avoid the most developed places and he doesn’t want “punitive” action against operators.

“Whatever we do we want to make sure it is going to be effective,” he said. “We don’t want to have mitigation be just a punitive measure. The ROD of 2008 says we may limit the pace of development and 10 years ago that might have been a good idea. But I don’t know if it is a good idea now. We may look at some other locations and intensity when new applications are submitted.”

Ultra’s Kelly Bott said of the trigger, “Mule deer mitigation has been an ongoing priority in the Pinedale Anticline for many years and Ultra supports continuing this approach. The recent mule deer impacts stem from the particularly harsh winter of 2016-17.” 

He added, “Ultra appreciates the importance of mule deer and will continue to support efforts advancing the vitality of the mule deer population. We also look forward to supporting future projects that will help offset the winter losses of the Mesa mule deer and the Sublette Herd Unit.”

WGFD with BLM and others review new natural resource extraction projects, “coordinating with them and industry on new mineral leasing, individual site development, exception requests and wildlife monitoring,” Damm said.


The largest factor for the plummeting population was the extremely harsh winter of 2016-17, which killed at least 90 percent of fawns and perhaps 35 percent of adults.

The Sublette herd seems to be rebounding, according to Damm. The annual herd count takes place later this month but WGFD just completed its post-hunting season survey with a focus on fawns and does.

“Given that the drivers of our populations are the does’ survival and annual fawn recruitment, we can get a good picture of the status of the population by focusing on those aspects,” Damm explained. “Doe survival continues to be very high. WGFD assesses fawn recruitment by the ratio of the number of fawns per 100 does, which was 68 during the latest post-season counts and slightly above the 10-year average of about 64.”

He added, “If the winter continues to be average or below in terms of winter range snow and temperatures, then recruitment into the population should be above average.”

Joy Ufford is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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