Polar bear and cubs scavenge bowhead whale carcass

A polar-bear mother in Alaska scavenges the bones of a bowhead whale as her cub and a companion play. Credit: Steven Kazlowski/NPL

Ecology

Polar bears turn to whale meat as their hunting grounds melt

But rarity of whales in some regions might deprive today’s bears of such emergency rations.

Warm periods in Earth’s history are hard on polar bears, which struggle to hunt for seals when sea ice declines. Now, research suggests that bears survived past warm spells by scavenging on whale carcasses.

Kristin Laidre at the University of Washington in Seattle and her team calculated that a single bowhead whale (Balaena mysticetus) provides as much food for a polar bear (Ursus maritimus) as do 1,300 ringed seals (Pusa hispida) — the bears’ main prey. The researchers analysed the population sizes of several Arctic whale species, and estimated the proportion of individuals that, rather than sinking to the seafloor when they die, float in the ocean and eventually wash onto land. In some areas, enough dead whales are available to temporarily buffer bears from starvation owing to sea-ice loss.

But the team says that this bounty might not be enough to sustain polar bears as the climate continues to warm. Whales are still scarce in many places because of whaling, and coastal and offshore development might block access to a stranded carcass.