ANCHORAGE, Alaska. — The U.S. Geological Survey is conducting a study that analyzes movements of 62 satellite-collared female polar bears over a 6-year period (2004-2009), providing a first description of swimming events within a population of polar bears. The results of the study have not yet been published, but are already generating significant attention.
In addition to describing the types of swims undertaken by the bears, the study suggests a relationship between long-distance swimming and the survival of cubs. Of 11 adult females that had cubs when they were collared and that later undertook a long-distance swim, 6 still had their cubs when subsequently “resighted” and 5 had lost their cubs. In comparison, of 7 females with cubs when they were collared that did not undertake a long-distance swim, 5 still had their cubs when subsequently “resighted,” and 2 had lost their cubs.
“The collars used on these bears were equipped with GPS technology, providing more detailed data on movements that allowed us to detect 50 swimming events, each over 50 kilometers,” said USGS researcher Anthony Pagano, who presented the new findings about the frequency, duration, and potential impacts of long-distance swimming events by polar bears at the International Bear Association biennial conference in Ottawa, Canada yesterday.
Half of the swims undertaken by the bears were from areas of unconsolidated sea ice to the main pack ice, with an average distance of 160 kilometers. Bears also swam from ice to land, from land to ice, and between points of land. All swimming events occurred between July and October, a time of year when sea ice is at its minimum. The study period encompassed the recent years of extreme sea ice retreat, including the most extreme retreat of 2007.
The polar bears were collared by USGS as part of a long-term study of the southern Beaufort Sea population shared by the U.S. and Canada.
Pagano is first author of a manuscript to be submitted to a wildlife journal in the near future. Co-authors include current USGS scientists George Durner and Kristin Simac, and former USGS scientists, Steven Amstrup and Geoff York. More information will be released upon publication.