This stands in contrast to their Beaufort near-neighbors: on average females greater than 1 year old weighed a little over 30 kg more, and similarly-aged males weighed on average 48.5 kg more, than those in the Beaufort. Additionally, the number of yearling cubs per female each spring-an indicator of reproductive success-was higher in the Chukchi.
So why should one sub-population of polar bears show signs of being so much healthier than another one close by? Rode, Regehr and colleagues noted that, although the number of ice-reduced days each year in the Chukchi increased from zero in 1986-94 to 44 in 2007-10, that was still half as many ice-reduced days as in the Beaufort. However, given that body condition remained the same in the Chukchi even as sea ice conditions deteriorated, they also looked to other explanations.
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The answer, they hypothesized, is the result of a suite of environmental differences between the two regions. For example, some southern Beaufort polar bears (and all the bears in western Hudson Bay) stay on land during the summer when ice retreats, while even during the seasonal minimum ice extent, sea ice persists over the continental shelf of the Chukchi. And while the majority of southern Beaufort bears inhabit the ice year-round, in the summer months that ice now retreats far north of the continental shelf, into the deeper, less productive waters of the polar basin.