Mesa deer population has stabilized
Contrary to BLM, report notes last year’s decrease due to reduced survival
by Julia Stuble

The mule deer population on the Pinedale Anticline has appeared to stabilize after sustaining a significant drop in population last year, according to the 2006 Annual Report for the Sublette Mule Deer Study.

This is the fifth year of the report compiled by Western EcoSystems Technology, Inc. (WEST), for Questar and the Bureau of Land Management. Last year’s study reported a substantial 46 percent population decrease in the Anticline mule deer herd over a winter which had significantly lessened winter drilling restrictions. This year’s report, detailing WEST Research Biologist Hall Sawyer’s results, found this year the population has stabilized.

The report also discussed the indirect impacts to habitat. It praised the liquid gathering system implemented by Questar and highlighted a new migration route. The study results also indicated that last year’s population drop is due mostly to reduced survival and not emigration, as the BLM has claimed.

The report found that over the life of energy development on the Mesa, the deer population has suffered over 1,300 acres of direct habitat losses due to the construction of well pads and access roads. This represents only about 2 percent of the Mesa, but the report adds that indirect habitat losses, which are difficult to measure, “appear to be substantially larger than the direct habitat losses.”

Of the direct habitat losses, the report indicated that the overwhelming majority of the loss (81 percent) was associated with well pads, not roads, even though over 68 miles of roads have been developed on the Mesa between 2000 and 2005. The report suggested that direct habitat loss can be decreased by emphasizing technologies which reduce well pad size and numbers.

Indirect habitat losses are sustained when deer habitat selection patterns are altered because of displacement or avoidance.

“The avoidance of areas near well pads created a functional loss of winter range that was substantially larger than the direct habitat loss incurred when native vegetation was removed during construction of a typical 3-4 well pad,” the report added.

The report also found that about half of areas considered “high use” prior to development could no longer be considered as such after the last five years of drilling.

Using radiocollared deer, WEST’s study illuminated a migration route paralleling the Wind River Front, and stretching for 40 miles. This route is only about a mile wide for its entire length. WEST found that deer had a “strong fidelity across seasons and years” for this route which was used by at least 3,500 deer.

“Given that the Pinedale Front and Mesa winter ranges are part of the larger Sublette population, this migration route may provide a well-defined and biologically important area for off-site mitigation efforts,” the WEST authors noted.

The report did suggest that deer had responded favorably to Questar’s liquid gathering system, which reduced over 1,000 truck trips a month to their lease holdings over the past year.

As part of a bargain for obtaining unrestricted winter drilling on select parts of the Anticline, Shell and Ultra have said they will commit to developing liquid gathering systems of their own.

Commenting on last year’s 46 percent population decrease, the report suggested that emigration had little to do with it, and blamed most of the loss on reduced survival.

The BLM has held that a significant amount of this population decrease was due to deer utilizing other winter ranges, while the Game and Fish have contended that they have not seen a significant shift.

This Annual Report noted, “The average emigration rate of 2 percent per year for the Mesa contributed to the observed population decline, but combinations of reduced adult and fawn survival were likely the driving factors.”

Although the BLM has touted its efforts to reduce winter disturbance to the deer by restricting winter drilling, this report found that disturbance from production activities need to be reduced as well.

“Mitigation measures designed to minimize disturbance to wintering mule deer in natural gas fields should consider all human activity across the entire project area and not be restricted to developing new wells,” the report noted.

The report concluded that the best mitigation measure is to reduce habitat loss to deer, which is best accomplished by setting a threshold for producing wells for an area and sticking to it.