Written by Dr. Steven Amstrup, Chief Scientist, Polar Bears International
After years of studying the denning behaviors of polar bears and testing the ability to find dens hidden under snow, two things are clear:
- A stable and uninterrupted denning process is essential to the survival of polar bear cubs. Cub loss was a leading factor contributing to the 40 percent decline of the Southern Beaufort Sea polar bear population between 2000 and 2010.
- Oil and gas companies are conducting aerial FLIR (forward-looking infrared) surveys to locate and hence protect maternal dens from disturbance. Those surveys miss over half of the polar bear dens within the surveyed areas.
The latter finding has direct relevance to the current U.S. Department of Interior proposal to allow hydrocarbon exploration and development on the Coastal Plain of the Arctic National Wildlife Refuge — the highest density denning area for this polar bear population.
Meet the Scientists
These findings appear in a new research paper published today in the journal PLOS ONE. Led by Dr. Tom Smith of Brigham Young University, the study was a collaboration with three scientists from Polar Bears International: BJ Kirschhoffer, Geoff York, and myself.
The four of us have decades of experience in polar bear research, including my more than 30 years as Polar Bear Project Leader in Alaska for the U.S. Geological Survey, where my work included studies of the Southern Beaufort Sea polar bear population.
Climate Has a Significant Bearing on Polar Bears Survival
Rapid loss of sea ice in the Southern Beaufort Sea has resulted in decreased cub survival and fewer cubs being born, highlighting the need to enhance the protection of maternal dens.
Pregnant polar bears dig dens in snowdrifts that form in autumn. They give birth in mid-winter and remain in their dens until spring when their cubs are finally large enough to survive the rigors of outside Arctic conditions.
While denning, polar bears are unable to simply move away from a disturbance without substantial risk to newborn cubs.
The polar bears that den on the Arctic Refuge Coastal Plain are part of the Southern Beaufort Sea population. Due to global warming-induced sea ice loss, the estimated size of this population has already declined by about 40 percent of what it was in the 1980s. Nearly one-third of pregnant polar bears in the Southern Beaufort Sea population depend on the Coastal Plain to give birth to their cubs.
FLIR Success Rates Are Unacceptably Low
I led the original testing of whether FLIR imaging could detect otherwise invisible dens in mid-winter and meet the challenge of locating dens so that they can be protected from possible industrial disturbances.
Working under optimal conditions where den locations were known, we found that FLIR imagery can detect many dens under the snow but cannot detect all dens and has many shortcomings. Subsequent research emphasized those shortcomings.
Our new study shows that in real-world conditions in actual practice, FLIR success rates are unacceptably low. And our team evaluated results of FLIR surveys oil-field operators conducted between 2004 and 2016. Consequently, we found that FLIR surveys only detected 45 percent of known dens. In other words, surveys missed more than half.
Although our paper points out that FLIR survey efficacy could be increased by following previously published operational guidelines, we concluded that weather and other factors, including den roof thickness, have always limited the effectiveness of FLIR.
Further, the accuracy of FLIR surveys is likely only to decline as global warming continues — bringing with it more humid and unpredictable weather.
New Den-Detection Methods Needed
Failures of past FLIR surveys to detect even a majority of polar bear dens suggests that denned mothers and cubs increasingly may be in harm’s way, elevating concerns about the proposed oil and gas exploration and development in the Arctic Refuge.
Given the threats to the Southern Beaufort Sea polar bear population, and, given that adherence to optimal FLIR protocols will be increasingly difficult in real-world conditions, where terrain, worsening weather, snow depth, and other factors impact FLIR’s accuracy, our study emphasizes the importance of developing and testing other den-detection methods.
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Dr. Steven C. Amstrup is chief scientist for Polar Bears International. He also is an adjunct professor at the University of Wyoming in Laramie. Before joining PBI, Amstrup was a research wildlife biologist with the United States Geological Survey at the Alaska Science Center, Anchorage AK., where he led polar bear research in Alaska for 30 years.