The polar bear population of the southern Beaufort Sea has fallen from 1500 to 900 over a period of nine years, a paper in Ecological Applications reports. Although this is just one of 19 polar bear populations on the planet, the findings are more significant than the usual stories of declines in subpopulations of threatened species.
As an apex predator, polar bears are essential for the health of the Arctic ecosystem. This, combined with their fierce beauty has made them pretty much the symbol for species under threat from Global Warming. It has made discussion about trends in polar bear numbers unusually politicized, with past estimates subject to furious claim and counter-claim.
The Beaufort Sea spans the border of Alaska and Canada; sea ice there has been in drastic decline with newly open water and larger waves forming a vicious circle.
The authors, coming from ten research institutions note, “prior investigations have linked declines in summer sea ice to reduced physical condition, growth, and survival of polar bears.” Their study not only found a decline in bear numbers between 2001 and 2010, but that most of the damage was done in 2004-6, which they note were, “years during which the spatial and temporal extent of summer sea ice generally declined.”
The lack of ice makes it hard for the bears to hunt prey such as seals. “Of the 80 cubs observed in Alaska from 2004 to 2007, only 2 are known to have survived,” said lead author Jeff Bromaghin of the U.S. Geologic Survey. Bears are left with the tough choice of staying with the ice as it retreats north or surviving on thin and jumbled floes closer to shore.
Equally worrying is that the number of juvenile bears continued to decline even when the adult population stabilized after 2008.
“The low survival may have been caused by a combination of factors that could be difficult to unravel,” said Bromaghin, “and why survival improved at the end of the study is unknown. Research and monitoring to better understand the factors influencing this population continue.”
While the M'Clintock Channel polar bear populations are reportedly increasing in the face of ice loss, and some other groupings are stable, the trend is down for the population as a whole. "If you're in the high Arctic, there's a greater possibility of population stability [because] there is more ice pack and prey availability," said David Koons to National Geographic. Koons is a National Geographic grantee who studies animal populations at Utah State University.
The USGS had better news this week for a different bear species. The Louisiana black bear, inspiration for millions of “Teddy Bears” worldwide, looks likely to survive the century, with habitat recovering.