12/8/2015 6:52:05 PM
More Polar Bears or Less Sea Ice?
A new paper sheds light on a question being asked by residents and researchers across the Arctic: Are people seeing more polar bears because there are more bears? Or are increased sightings due to sea ice losses that are shifting more bears onshore where people are more likely to see them?
To tease out the answer, lead author Karyn Rode from the USGS Alaska Science Center examined two data sets from collared adult females in the Chukchi Sea, a population shared by Alaska and Russia. Analyzing location data from both 1986-1995 and 2008-2013, researchers from the USGS, U.S. Fish and Wildlife Service, and Brigham Young University were able to compare land use during a period of relatively stable ice (earlier) versus a later period of rapid ice loss.
As with polar bears across their range, bears in the Chukchi Sea prefer sea ice. They spent the majority of their time offshore in both time periods. However, their land use nearly doubled during the low ice period, with the time spent on land for >7 days going from approximately 20% in the early period to nearly 40% in the later period. The number of days spent onshore also grew longer. In years with greatly reduced summer sea ice habitat, the bears stayed on land an average of 30 days longer.
The analysis also confirmed the continued importance of both Wrangel and Herald Islands in the Chukotka area of Russia as critical habitat for this population of polar bears. The majority of adult females coming ashore in the Chukchi Sea area chose one of these two islands, which are renowned as polar bear nurseries due to their importance as denning sites. While not reflected in this study, reports from community polar bear patrols across mainland Chukotka also suggest increasing use of the mainland by polar bears.
These results are consistent with studies showing increased use of land in other regions and raise concerns for polar bear management and long term conservation. Studies have shown that polar bears are not effective at foraging onshore and typically fast during the ice-free season. Coupled with that, recent analysis has confirmed that terrestrial foods do not meet the energetic requirements of a species that has evolved for a high fat diet, nor do these foods occur in sufficient abundance or distribution across the polar bear's range.
This study also validates concerns that frontline managers have expressed regarding increasing polar bear-human interactions. As more bears spend longer times ashore without adequate hunting opportunities, we are likely to see increased conflicts with people. At the same time, reduced sea ice cover in the summer is opening the Arctic to increased human activities from research to tourism to industrial explorations and exploitation. This highlights the need for increased vigilance, investment, and cooperation by all who live, work, or recreate in the Arctic to be fully prepared to mitigate negative polar bear-human encounters.