Sharp decline in polar bear population

An international team of scientists led by researchers from the U.S. Geological Survey has found that the polar bear population in the southern Beaufort Sea declined by about 40 percent between 2001 and 2010, the USGS has reported. The scientists attribute much of the decline to a low survival rate of polar bear cubs between 2004 and 2006.

“Of the 80 cubs observed in Alaska from 2004 to 2007, only two are known to have survived,” said Jeff Bromaghin, USGS research statistician and lead author of the study.

Despite some improvement in the survival rates of both young bears and adults, starting in 2007, the survival rate of juvenile bears declined during the entire study period. By 2010 the bear population had stabilized at about 900 animals, the USGS says.

Bromaghin says that the reason for the low survival rates remains unknown, with a combination of different factors possibly contributing to the population decline. One possible culprit is a lack of adequate access to seals, the bears’ predominant prey. During the fall open water season, many bears stay on the sea ice as it retreats to an ever diminishing sea ice extent, leaving the bears at considerable distances from shore areas that seals are thought to predominantly inhabit, USGS says. In the winter, the increasingly thin and mobile sea ice is more susceptible to breaking up and rafting than in past years, leading to jumbled ice conditions that may make the capture of seals more difficult, the agency says.

Of 19 Arctic polar bear populations, four, including the southern Beaufort Sea population, are thought to be in decline, five are stable and one is increasing - there is insufficient data to determine population trends in the remaining populations, USGS says.

- Alan Bailey