There has been a dramatic reduction in the extent of summer sea ice in the Arctic since 1870, Chart 1.
Australian television’s Four Corners showed a program on August 4, 2008, entitled ‘Tipping Point’ claiming that the disappearance of summer sea ice in the Arctic could have drastic consequence for polar bears.
Interestingly there is no summer sea ice in western Hudson Bay in the Canadian Arctic and there are polar bears.
According to polar bear experts, Douglas Clark and Ian Stirling (1998), “The polar bear population that inhabits western Hudson Bay spends the period from late July through early November on shore because the annual ice melts completely.”
Scientists previously thought that these polar bears sustained themselves on stored fat during this ice-free period, however, Derocher et al (1993), found that juvenile males and female polar bears would eat vegetation, such as alpine blueberries, crowberries, grasses and sedge, when marine mammals were unavailable because of the absence of summer sea-ice. This conclusion was based on examination of droppings and observations of signs of feeding on berries, such as berry stained teeth and fur, on polar bears captured in inland areas of western Hudson Bay between 1986 and 1992.
While there is evidence that females and offspring eat berries during the ice-free period, it is unclear whether eating berries significantly contributes to the total energy budget of polar bears. However, Derocher et al argue that eating vegetation “could significantly influence the condition of bears and in turn influence survival, particularly of cubs” and that “the patterns found in western Hudson Bay illustrate the physiological and behavioural plasticity of polar bears.”
Douglas C. Clark and Ian Stirling, ‘Habitat Preferences of Polar Bears in the Hudson Bay Lowlands during Late Summer and Fall’, (1998) Ursus 10, pp 243-250 at 243 and 248.
Andrew E. Derocher, Dennis Andriashek and Ian Stirling, ‘Terrestrial Foraging by Polar Bears during the Ice-Free Period in Western Hudson Bay’, Arctic (1993) 46(3), pp 251-254 at 251 and 253.
ABC 4 Corner’s ‘The Tipping Point, broadcast August 4, 2008. Reporter: Marian Wilkinson