Nov. 16, 2006 — Far fewer polar bears cubs are surviving off Alaska's northern coast than in years past, a federal government report released Wednesday has concluded.
The study of polar bears in the south Beaufort Sea, which spans the northern coasts of Alaska and western Canada, also found that adult males weigh less and have smaller skulls than those captured and measured two decades ago.
The study does not directly blame the changes on a decline in sea ice. However, fewer cubs and smaller males are consistent with other observations that suggest changes in sea ice may be adversely affecting polar bears, the study said.
The study warns that the decline in cub survival and the smaller adult males are the same conditions that preceded a decline in the polar bears of western Hudson Bay, Canada, where the population dropped 22 percent in 17 years.
Advocates seeking protections for U.S. polar bears say the report proves their point.
"It's just another example of seeing all of the impacts that scientists have previously predicted coming to pass," said Kassie Siegel of the Center for Biological Diversity in Joshua Tree, Calif. Siegal is the lead author of the petition seeking to list polar bears as threatened under the Endangered Species Act.
"The Grim Reaper of global warming is now clearly killing polar bear cubs," said Deborah Williams, president of Alaska Conservation Solutions, an Anchorage-based group aimed at halting climate change. "This study should be interpreted as a cry from the North to reduce greenhouse gases."
The report stopped short of saying the Beaufort Sea polar bear population, one of two in Alaska, had declined.
However, "Significant changes in cub survival and physical stature must ultimately have population level effects," the report concluded.
The report estimates the Beaufort Sea polar bear population at 1,526, down from a previous estimate of 1,800 bears. That would be a 15 percent decline, but researchers said the current study used different methods of counting.
The Beaufort Sea bears is one of two Alaska stocks. The other is the Bering-Chukchi stock off Alaska's northwest coast, a population shared with Russia.
Polar bears are classified as marine mammals because they spend much of their lives on sea ice. The listing petition claims that polar bears are threatened because of drastic declines in ocean ice due to global warming. A decision by the U.S. Fish and Wildlife Service on listing America's polar bears as threatened is due next month.
Polar bears depend entirely on sea ice for survival, according to the USGS report. Warming has caused major changes and scientists foresee more melting.
"Because more profound declines in sea ice area and extent are predicted for these northern regions, continued monitoring and conservative management of the SBS (Southern Beaufort Sea) polar bear population is warranted," the report concluded.
Siegel said the effects of shrinking sea ice are occurring exactly as summarized by the scientists quoted in her group's listing petition.
"Only it's happening sooner than they thought," she said.
The USGS report compared data on cubs collected from 1990 through last spring to studies from 1967-89.
Females give birth in January and emerge from dens with new cubs in March or early April. Cubs typically accompany their mother for 2 to 3 years.
For polar bears measured during autumn months, the number of surviving cubs born that spring declined from a mean of .61 cubs per female to a mean of .25 cubs per female.
"This decline can only be explained by lower survival of cubs after den emergence," the report said.
