Polar bears are good swimmers and have always been able to cross a large amount of freezing water in search of food and a place to sleep on the ice, but melting polar ice is forcing them to make much longer swims, according to an article in the Washington Post.
Biologist Andrew Derocher, from the University of Alberta, has been tracking polar bears in the waters off the coasts of Alaska and Canada for the last six years, and has monitored over 100 of the animals. His data is showing that the bears are making more and more long-distance swims across the open ocean, and that effort is taking a toll on their health and well-being.
Polar ice is melting so quickly in some spots, according to Derocher, the animals are being caught in areas with little or no ice on which to stand, much less feed and raise a family. His research shows that in 2004, only 25 percent of the bears being monitored took a long-distance swim, defined as more than 50 kilometers, or about 31 miles. By the year 2012, that number had increased to 69 percent of the monitored population.
Derocher adds while the bears are definitely good swimmers, they did not evolve to make long-distance treks, and are fairly slow in the water, usually moving at a rate of about two kilometers per hour. Taking an entire day to cross 30 miles of open water does not allow a bear to rest or eat, resulting in loss of body weight for adult bears and often death for the cubs that may be traveling with the mother.
Derocher called the journey for a cub a “death sentence.” He adds most bears with cubs will walk for extremely long distances to avoid swimming if they have cubs in tow. When he first began to study the bears in the 1980s, such long-distance swims were rare, because there was no need to make them. Today, melting ice is causing the ice platforms from which bears dive to catch seals and other prey to become smaller and more spaced out.
This information, along with an earlier study that found the population of bears in the souther Beaufort Sea had fallen somewhere between 25 and 50 percent during a period from 2001-2010, is leading to major concerns for the entire polar bear population.
Derocher added we are seeing bears with lower body fat, needed to survive the cold, and fewer cubs, and also noted the bears were being forced to change their hunting habits.