Natural gas development appears to have negatively affected the population size and distribution of wintering mule deer in southwestern Wyoming, but mitigation by producers may be succeeding, a seven-year study has concluded.
The study assessed the potential impacts of energy development in the Pinedale Anticline area between 2001 and 2007. The 118-page study was conducted by Cheyenne, WY-based Western EcoSystems Technology Inc. (WET) and funded by the Bureau of Land Management's Pinedale office, the Wyoming Game and Fish Department and Questar Exploration and Production. Besides major funding by Pinedale operator Questar, Shell Exploration & Production Co. and Ultra Resources Inc., which also both operate in the region, provided funds for the project.
Data collected from the Mesa area of the Pinedale Anticline indicated that mule deer numbers declined in the first four years (2001-2004) of the study. However, the deer's numbers increased from 2005-2007, for an overall decline rate of 30% over the entire period. When survival and recruitment rates estimated from the Mesa were incorporated into a population growth model, the model predicted a 27% decline, the study noted. Over the same time period, the Wyoming Game and Fish Department had estimated a 10% decline for the larger Sublette Herd Unit, which included the Mesa and several other winter ranges.
"There is no evidence that suggests other segments of the Sublette mule deer population declined a comparable rate" to the Mesa area, noted the study.
Producers, however, said they were encouraged that the mule deer population increased in the last three years of the study, which reflects industry efforts to mitigate drilling impacts in the region.
The study found that through 2007, gas field development in the Mesa portion of the Pinedale Anticline Project Area (PAPA) resulted in 1,520 acres of direct habitat loss from the construction of well pads and access roads. Most (83%) habitat loss was associated with well pads, particularly as gas field development progressed. Direct habitat loss represented less than 3% of the Mesa surface area, but it did not include the relatively short-term losses from pipeline construction.
"Given the number of wells approved in the PAPA, directional drilling strategies have reduced direct habitat loss by drilling multiple wells (up to 28) from single pads," the study said.
According to WET, the results "suggest that efforts to minimize direct and indirect habitat loss should focus on technology and planning that reduce the number of well pads and the human activity associated with them. Specifically, our results indicate that indirect habitat loss associated with producing well pads may be reduced by 38-63% with the installation of LGS [liquids gathering systems]."
WET also reported that even though there were changes in winter habitat selection and distribution patterns in the study period, "the migration routes of mule deer to and from the Mesa remained intact and functional." Most mule deer on the Mesa did not move more than 1.6 kilometers/day, and movements were generally restricted to a relatively small home range, according to the study.
The study is available at www.west-inc.com in the "Articles, Reports and Proceedings" section under "Large Mammal Studies."
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