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South­ern Beau­fort Sea polar bear pop­u­la­tion declined in the 2000s

pub­lished 22 Novem­ber 2014 | mod­i­fied 22 Novem­ber 2014

In a recently pub­lished new polar bear study, sci­en­tists from the United States and Canada found that dur­ing the first decade of the 21st cen­tury, the num­ber of polar bears in the south­ern Beau­fort Sea expe­ri­enced a sharp decline of approx­i­mately 40 percent.

Polar bear arctic seaThe sci­en­tists, led by researchers at the U.S. Geo­log­i­cal Sur­vey, found that sur­vival of adult bears and cubs was espe­cially low from 2004 to 2006, when most of the decline occurred. The paper “Polar bear pop­u­la­tion dynam­ics in the south­ern Beau­fort Sea dur­ing a period of sea ice decline” was pub­lished online ahead of print on 17 Novem­ber in the jour­nal Eco­log­i­cal Appli­ca­tions.

Of the 80 cubs observed in Alaska from 2004 to 2007, only 2 are known to have survived
Jeff Bro­maghin, lead author, USGS research statistician »

Sur­vival of adults and cubs began to improve in 2007 and the pop­u­la­tion sta­bi­lized at approx­i­mately 900 bears in 2010, the last year of the study. How­ever, the sur­vival of juve­nile bears declined through­out the 10-​year study period (20012010), sug­gest­ing that con­di­tions remained unfavourable for young bears newly sep­a­rated from their mothers.

Sci­en­tists sus­pect that lim­ited access to seals dur­ing both sum­mer and win­ter con­tributed to low sur­vival dur­ing this period. Although some bears in this pop­u­la­tion now come onshore dur­ing the autumn open water period, most stay with the sea ice as it retreats north into the Arc­tic Basin and far from shore where few seals are thought to occur. Sim­i­larly, the thin­ning and increas­ingly mobile win­ter ice is sus­cep­ti­ble to break­ing up and raft­ing, which can cre­ate rough and jum­bled ice con­di­tions that may make it harder for polar bears to cap­ture seals. How­ever, other poten­tial causes, such as low seal abun­dance, could not be ruled out.

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.”

The Polar Bear Spe­cial­ists’ Group of the Inter­na­tional Union for the Con­ser­va­tion of Nature will use the new esti­mate for the south­ern Beau­fort Sea pop­u­la­tion to track his­toric (within the last 25 years) and cur­rent (within the last 12 years) trends in the 19 polar bear pop­u­la­tions world­wide. Cur­rently, four pop­u­la­tions, includ­ing the south­ern Beau­fort Sea pop­u­la­tion, are con­sid­ered to be declin­ing, five are sta­ble, one is increas­ing, with the remain­der con­sid­ered to be data deficient.

A Point of View (POV)video – first ever – from a free-​ranging polar bear on Arc­tic sea ice in spring 2014:

(Source: U.S. Geo­log­i­cal Sur­vey (USGS) YouTube channel)

Col­lab­o­ra­tors with USGS in the study included Envi­ron­ment Canada, Uni­ver­sity of Alberta, U.S. Fish and Wildlife Ser­vice, Polar Bears Inter­na­tional, and West­ern Ecosys­tems Technology.

The polar bear was listed as glob­ally threat­ened under the U.S. Endan­gered Species Act in 2008 due to con­cerns about the effects of sea ice loss on their pop­u­la­tions. The Inter­na­tional Union for Con­ser­va­tion of Nature (IUCN) has listed the polar bear as Vul­ner­a­ble in their Red List of Threat­ened Species™, based on a sus­pected pop­u­la­tion reduc­tion of more than 30% within three gen­er­a­tions (45 years) due to decline in area of occu­pancy, extent of occur­rence and habi­tat quality.

(Source: USGS news release, 17.11.2014)

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