A group of biologists that have been studying polar bears off the coast of Alaska have determined that polar bear cubs are drowning, due to loss of sea ice. They are being forced to make longer swims than normal just to find land or stable ice sheets.
The study confirms the dangers of ice loss to Alaska’s polar bear population. It’s been widely theorized that adult polar bears have been forced to cross ever-longer stretches of open ocean as the polar regions heat up. The new work, by U.S. Geological Survey Alaska Science Center researchers, confirms that theory. It also reveals that these open-water swims have a dramatic effect on young cubs, which are forced to follow their mothers in search of food and solid ground.
“This research is the first analysis to identify a significant multi-year trend of increased long-distance swimming by polar bears,” co-author Geoff York said Monday. “Climate change is pulling the sea ice out from under polar bears’ feet, forcing some to swim longer distances to find food and habitat.”
The researchers have been tracking the bears with GPS tracking collars in order to determine the extent of their journeys. Of the bears that were tracked, eleven bears that swam long distances had young cubs at the time of the collar deployment. Five of those bears lost their cubs while swimming, a 45 percent mortality rate. Among cubs not compelled to swim long distances, the mortality rate was 18 percent.
“Adult polar bears are strong swimmers,” York said. “But they can’t hold their noses while swimming, so they’re at risk for drowning if a storm hits. Cubs are at even greater risk. Their smaller body size leaves them more prone to hypothermia, and they don’t have the energy reserves of the adult bear. They can’t feed while swimming, and it takes a lot of energy to keep up with mom.”
According to a report from the National Snow and Ice Center in Boulder, Colorado, this June, less sea ice covered the Arctic than in any year, save one, since records began in 1979. They also stated that 2011 is now on track to drop below the record-low ice minimum set in 2007. Arctic sea ice usually reaches its lowest point during the first week of September, which means those cubs may be doing a lot more swimming this summer.
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