Historical and potential future importance of large whales as food for polar bears

Polar bears (Ursus maritimus) are expected to be adversely impacted by a warming Arctic due to melting of the sea-ice platform from which they hunt ice-breeding seals. We evaluated the hypothesis that scavenging on stranded large whale carcasses may have facilitated polar bear survival through past interglacial periods during which sea-ice was limited by analyzing: (1) present-day scavenging by polar bears on large whale carcasses; (2) energy values of large whale species; and (3) the ability of polar bears, like the brown bears (Ursus arctos) from which they evolved, to quickly store large amounts of lipids and to fast for extended periods. We concluded that scavenging on large whale carcasses likely facilitated survival of polar bears in past interglacial periods when access to seals was reduced. In a future, ice-impoverished Arctic, whale carcasses are less likely to provide nutritional refuge for polar bears because overharvesting by humans has greatly reduced large whale populations, carcass availability is geographically limited, and climate-induced sea-ice loss is projected to occur at a more rapid pace than polar bears have experienced at any previous time in their evolutionary history.