• Mass loss rates of fasting polar bears

      Pilfold, Nicholas W.; Hedman, Daryll; Stirling, Ian; Derocher, Andrew E.; Lunn, Nicholas J.; Richardson, Evan (2016)
      Polar bears (Ursus maritimus) have adapted to an annual cyclic regime of feeding and fasting, which is extreme in seasonal sea ice regions of the Arctic. As a consequence of climate change, sea ice breakup has become earlier and the duration of the open-water period through which polar bears must rely on fat reserves has increased....
    • Migratory response of polar bears to sea ice loss: to swim or not to swim

      Pilfold, Nicholas W.; McCall, Alysa; Derocher, Andrew E.; Lunn, Nicholas J.; Richardson, Evan (2017)
      Migratory responses to climate change may vary across and within populations, particularly for species with large geographic ranges. An increase in the frequency of long-distance swims (> 50 km) is one predicted consequence of climate change for polar bears Ursus maritimus....
    • Polar bear ( Ursus maritimus ) migration from maternal dens in western Hudson Bay

      Yee, Meredith; Reimer, Jody; Lunn, Nicholas J.; Togunov, Ron R.; Pilfold, Nicholas W.; McCall, Alysa G.; Derocher, Andrew E. (2017)
      Migration is a common life history strategy among Arctic vertebrates, yet some of its aspects remain poorly described for some species. In February-March, post-parturient polar bears (Ursus maritimus) in western Hudson Bay, Canada, migrate from maternity den sites on land to the sea ice with three- to four-month-old cubs....
    • Ringed seal (Pusa hispida) tooth annuli as an index of reproduction in the Beaufort Sea

      Nguyen, Linda; Pilfold, Nicholas W.; Derocher, Andrew E.; Stirling, Ian; Bohart, Alyssa M.; Richardson, Evan (2017)
      Multi-decadal time-series of biological indices that reflect the state of a population are rare in ecological studies, but invaluable for assessing environmental regulation of population dynamics. We utilized canine teeth extracted from ringed seals (Pusa hispida) killed by polar bears (Ursus maritimus) in the Beaufort Sea, Canada, in 1985–2011, to obtain widths of annual growth layers in the cementum....
    • Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity

      Rode, Karyn D.; Wilson, Ryan R.; Douglas, David C.; Muhlenbruch, Vanessa; Atwood, Todd C.; Regehr, Eric V.; Richardson, Evan S.; Pilfold, Nicholas W.; Derocher, Andrew E.; Durner, George M.; et al. (2018)
      The effects of declining Arctic sea ice on local ecosystem productivity are not well understood but have been shown to vary inter-specifically, spatially, and temporally. Because marine mammals occupy upper trophic levels in Arctic food webs, they may be useful indicators for understanding variation in ecosystem productivity. Polar bears (Ursus maritimus) are apex predators that primarily consume benthic and pelagic-feeding ice-associated seals. As such, their productivity integrates sea ice conditions and the ecosystem supporting them. Declining sea ice availability has been linked to negative population effects for polar bears but does not fully explain observed population changes. We examined relationships between spring foraging success of polar bears and sea ice conditions, prey productivity, and general patterns of ecosystem productivity in the Beaufort and Chukchi Seas (CSs). Fasting status (?7 days) was estimated using serum urea and creatinine levels of 1,448 samples collected from 1,177 adult and subadult bears across three subpopulations. Fasting increased in the Beaufort Sea between 1983–1999 and 2000–2016 and was related to an index of ringed seal body condition. This change was concurrent with declines in body condition of polar bears and observed changes in the diet, condition and/or reproduction of four other vertebrate consumers within the food chain. In contrast, fasting declined in CS polar bears between periods and was less common than in the two Beaufort Sea subpopulations consistent with studies demonstrating higher primary productivity and maintenance or improved body condition in polar bears, ringed seals, and bearded seals despite recent sea ice loss in this region. Consistency between regional and temporal variation in spring polar bear fasting and food web productivity suggests that polar bears may be a useful indicator species. Furthermore, our results suggest that spatial and temporal ecological variation is important in affecting upper trophic-level productivity in these marine ecosystems.