Changes in polar bear habitat

Two of the great challenges facing polar bear conservation in the face of climate warming are the huge areas involved and the fact that their habitat is disappearing. The home range size of polar bears vary from fjord-living bears, which may use an area of only 5000 km2, to pelagic bears, which use areas of over 300,000 km2 (Garner et al, 1991; Mauritzen et al, 2001).

In terrestrial ecosystems, conservation biologists can look to habitat restoration or habitat protection measures to improve the conservation status for a species. In stark contrast, there are no such methods available for the conservation of polar bears. Supplemental feeding is one option open to sustaining food stressed polar bears, but sourcing the amounts of food that would be required would be a daunting task and harvesting seal populations that are also being affected by climate warming would seem unwise and unsustainable.

Relocating polar bears to higher latitudes may seem logical but there are few indications that these ecosystems have spare capacity to sustain more animals. Even as the sea ice begins to melt away at high latitudes, the solar radiation in these areas will not change and the short growing season will limit the primary productivity that drives the system. Some have suggested that climate change could improve habitat for polar bears in areas that are currently covered by thick multi-year ice. The problem is that these areas are small relative to the distribution of the bears, and while they may provide new habitat for a while, continued climate warming will eventually erode these areas as well.

The Arctic Ocean at the top of the planet is currently covered by permanent polar pack ice and is another area that could act as a refuge for the bears, but, unfortunately, those waters are deep, cold and biologically unproductive. Further, bearded seals would be unlikely to survive there because they are benthic feeders (feed on the ocean bottom) and cannot dive to the ocean floor in the deep waters of the Arctic Ocean. Predictions are now clear that the Arctic Ocean will become ice-free in summer and at a much more accelerated rate than earlier thought (Comiso, 2002; Stroeve et al, 2007). Populations from the Beaufort Sea westward to Svalbard, Norway all rely on the permanent polar pack ice as a summer refuge area. If the permanent polar pack ice melts away during summer, any animals in this area would be stranded far from land with possibly dire consequences.

More radical conservation measures, such as captive rearing, are useful for species that can be warehoused until their numbers are sufficient to be released in secure habitats. However, if the sea ice cannot support polar bears, it is unclear what conservation value these bears could provide.

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