Mule deer & energy development impacts
by Cat Urbigkit, Pinedale Online!
June 25, 2017
Hall Sawyer of Western Ecosystem Technology, Inc. and colleagues have published a paper, "Mule deer and energy development – Long-term trends of habituation and abundance" in the journal Global Change Biology that may have an impact on plans for future energy development in the West.
The study concentrated on the Pinedale Anticline's mule deer population as the natural gas field was developed. Using telemetry data from 187 deer during a 17-year period (including two years predevelopment), the researchers assessed whether mule deer habituated to development and if their response varied with winter severity, and measured the abundance of deer to indirectly link behavior with demography. The study took place from 2001-2015.
The researchers found: "Mule deer consistently avoided energy infrastructure through the 15-year period of development and used habitats that were an average of 913 m further from well pads compared with predevelopment patterns of habitat use. Even during the last 3 years of study, when most wells were in production and reclamation efforts underway, mule deer remained >1 km away from well pads. The magnitude of avoidance behavior, however, was mediated by winter severity, where aversion to well pads decreased as winter severity increased.
"Mule deer abundance declined by 36% during the development period, despite aggressive onsite mitigation efforts (e.g. directional drilling and liquid gathering systems) and a 45% reduction in deer harvest. Our results indicate behavioral effects of energy development on mule deer are long term and may affect population abundance by displacing animals and thereby functionally reducing the amount of available habitat."
The steep decline in mule deer abundance may have numerous causes. As the researchers noted, "Although our results are consistent with a population decline caused by indirect habitat loss and ensuing density dependence, the observed population decline could alternatively be explained by:
(1) wide spread mule deer declines across a larger region; or
(2) emigration of mule deer from the study area to avoid disturbance.
Nevertheless, abundance estimates from the Sublette herd unit declined by only 16% during the same period—a decline that largely may have been caused by trends on the Pinedale Anticline, which was included within the Sublette herd unit."
This paper indicates that its findings contradict many federal land planning assessments (NEPA documents) that consider natural gas development a short-term impact to which animals readily habituate once drilling activities are completed. "However, our long-term dataset comprising multiple generations of animals indicates that avoidance of energy infrastructure is a long-term effect that can be associated with significant population declines."
The authors also noted the extensive onsite mitigation measures that were included in Pinedale Anticline's development that were designed to mitigate the impact of energy development on wintering mule deer, while reducing the amount of habitat loss and human disturbance, may have averted an even larger population decline.
The study's implications is future mitigation strategies is significant: "Our study indicates that impacts of energy development in sagebrush steppe can be long term, if not permanent, and mitigation measures should be accordingly long term. Second, minimizing impacts through onsite mitigation, although desirable for species that exhibit high site fidelity, may not be possible. Onsite mitigation was insufficient to abate behavioral and demographic consequences to mule deer during our study.
"Third, given the limitations of onsite mitigation, avoidance of impacts by strategically foregoing leasing or reducing intensity of development of critical habitats is likely the most effective approach to averting population-level impacts.
"And finally, where avoidance and minimization are not possible or effective, offsite mitigation approaches such as biodiversity offsets or conservation banks that aim to compensate for biological impacts in one area with protected or improved habitat elsewhere are untested but warrant consideration."
The authors conclude: "Our long-term study refutes the prevailing notion that mule deer habituate to human disturbance, and instead, demonstrates that energy development can have long-term consequences for deer populations simply through avoidance behavior and the indirect habitat loss that ensues. Furthermore, as the NEPA process is based on full disclosure of the potential impacts from a proposed action, our work indicates that future impact assessments should disclose that the impacts to ungulate habitat in the shrub-steppe environment of the West may well be long-term and perhaps an irretrievable commitment of resources."
To read the entire paper, see the link below.
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