The Disappearance of the Great Hunt

Polar bears occupy a unique niche in the Arctic. They are extraordinary terrestrial hunters who prey on some of the largest aquatic animals found in the Arctic, including beluga whales and ringed seals, the main source of their diet. Blue Planet  portrays the increasing struggle that polar bears face: feeding their offspring and themselves in a disappearing environment.

Polar bears require a high caloric diet, and on average a polar bear needs 2.2kg of fat each day to maintain their required energy, and much of this fat is obtained from eating their prey, the ringed seal [1]. A ringed seal, weighing in at almost 60 kg on average, can sustain a polar bear’s energy to last over a week [1]. Due to recent climate changes, the sea-ice platforms where polar bears hunt their prey are melting earlier in the spring season, providing less time for polar bears to hunt for seals and seal pups lairs hidden underneath the ice [2]. This is a grave concern, as it can alter the energy budget of polar bears going into the warmer seasons.

In fact, there is already evidence of polar bear prey switching.  In the Western Hudson Bay, prey switching is seen with a decreased frequency of seal and increased frequency of geese and eggs in polar bear diet [2].  Cubs learn to hunt by watching the mother bear hunt. Watching their mothers change hunting patterns from seals to geese causes later generations of polar bears to learn to hunt terrestrial prey instead of traditional aquatic animals. As climate change continues, polar bears will need to spend “more time ashore,” leading to an increase in terrestrial predation, and while polar bears have relatively inefficient terrestrial locomotive ability, chasing geese still results in a net caloric gain [3].  Prey switching to bowhead whales in coastal regions has also been observed, with whales making up to 70% of the fall diet of some polar bears [4]. As climate change continues in the Arctic, polar bears lose the icy terrain they are able to hunt their traditional prey. Instead, they must adapt to hunt more accessible species, ending the era of the great hunt.

by Saba Hossain, Elizabeth Miller and Zach Zlatin

Blue Planet, Frozen Seas, Season 1, Episode 4, 15:50

References

  1. Galicia MP, Thiemann GW, Dyck MG, Ferguson SH and JW Higdon JW. 2016. Dietary habits of polar bears in Foxe Basin, Canada: possible evidence of a trophic regime shift mediated by a new top predator. Ecology and Evolution16:6005–6018.
  2. Gormezano LJ, Ellis-Felege SN, Iles DT and A Barnas. 2017. Polar bear foraging behavior during the ice-free period in western Hudson Bay: observations, origins, and potential significance. American Museum Novitates 3885:1-28
  3. Gormezano, Linda J, et al.  2016. Costs of locomotion in polar bears: when do the costs outweigh the benefits of chasing down terrestrial prey?  Conservation physiology 4.1: cow045.
  4. Rogers, MC, et al. 2015. Diet of female polar bears in the southern Beaufort Sea of Alaska: evidence for an emerging alternative foraging strategy in response to environmental change.  Polar Biology 38.7: 1035-1047.

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