Deer herd stable, corridor intact

by Cat Urbigkit

Following nearly six years of gas field development in the Pinedale Anticline Project Area, the mule deer winter range on the Mesa has incurred 1,300 acres of direct habitat losses from the construction of well pads and access roads.

Research indicates that mule deer abundance declined by 46 percent in the first four years of gas development and then appeared to stabilize during the fifth year, according to the 2006 Annual Report for the Sublette Mule Deer Study.

The Western EcoSystems Technology, Inc. study is in its fifth year, with funding provided by Questar Exploration and Production Company, Wyoming Game and Fish Department and the Pinedale Bureau of Land Management.

Although 68 miles of roads were built on the Mesa between 2000 and 2005, researchers now suggest that the efforts to minimize direct habitat losses should focus on technology or development plans that reduce the size and/or number of well pads.

Researchers found that deer avoided well pads four of the five years of development and only 48 percent of areas considered ‘high use’ prior to development were considered ‘high use’ after five years of development. Direct and indirect habitat losses reduce the size of the winter range available to mule deer and may reduce the carrying capacity of that range.

The report noted: “Despite significant changes in winter habitat selection and distribution patterns during years of gas field development, the migration routes of mule deer to and from the Mesa have remained intact and functional.”

The researchers identified a distinct 40-mile migration route that parallels the base of the Wind River Range and has an average width of only 1.2 miles.

The researchers noted, “Because our marked deer occupied different mountain ranges during the summer, we know that their migration routes eventually diverged from this well-defined corridor.”

“Given that the Pinedale Front and Mesa winter ranges are part of the larger Sublette population (herd unit), this migration route may provide a well-defined and biologically important area for off-site mitigation efforts aimed at the entire Sublette deer herd,” the report stated.

The WEST report noted that the winter of 2005-06 marked the first year of approved multiple pad year-around drilling on the Mesa while it was also the first winter for implementation of two major mitigation measures to reduce human disturbance: installation of a fluids collection system, and closure of the west access road to the Mesa and the use of locked gates on other Mesa-area roads.

Liquids from producing wells operated by Questar Exploration and Production Company were gathered in pipelines rather than being removed from tanks on individual pads by tanker trucks, eliminating 25,000 truck trips per year.

According to the WEST researchers, “our preliminary results suggest that deer responded positively to both the fluids collection system and roads with reduced traffic levels.”

The report spent some time on the issue of migration bottlenecks, noting that bottlenecks create management concerns because the potential to disrupt or sever migratory routes is believed to be greater in these areas compared to areas where animal movements are less restricted.

Across the roughly 40-mile migration corridor subject to the study, researchers identified two bottlenecks adjacent to large water bodies where the corridor narrowed to less than half-mile in width.

However, depending on what definition of narrow or limited is used, the migration corridor in the local study area could be considered one contiguous bottleneck.

The report noted, “It appears that a relatively small human-related development or other movement barrier could potentially disrupt the effectiveness of this corridor. Based on previous studies and population estimates, a minimum of 3,500 mule deer are believed to migrate through this corridor and are known to occupy portions of five different mountain ranges during the summer (i.e., Wind River Range, Gros Ventre Range, Snake River Range, Wyoming Range, Salt River Range) in western Wyoming.”

“Given that this corridor provides the mechanism for thousands of deer to congregate on a common winter range and distribute themselves across multiple summer ranges, the importance of protecting this migration corridor is evident and will be a key to the long-term maintenance of this population,” the report concluded.