It's well known that polar bears are the top predator in the Arctic, each one killing a seal every three to five days.
What hasn't been well understood is just how much carrion the estimated 26,000 polar bears leave behind once they finish dining on seal blubber. It turns out that with each polar bear abandoning about 300 kilograms of biomass every year, the total amounts to more than seven million kilograms, says the University of Alberta's polar bear expert Andrew Derocher - enough to feed a wide range of scavengers.
"It's a staggering amount," which has an enormous impact on the ecosystem, says the professor in the Department of Biological Sciences. At least a third of a seal carcass is normally left for scavengers such as Arctic foxes, gulls, ravens and even other polar bears. Snowy owls, wolves and grizzly bears have also been observed consuming the leftovers.
"There are so many different species, depending on where you are, that exploit polar bear kills," says Derocher.
Derocher and his international collaborators - most of whom are former U of A doctoral students - published their latest study on polar bear carrion in the journal Oikos in October. Much of the research was funded by the San Diego Zoo Wildlife Alliance, which has just provided an additional $100,000 per year for three years for further study.
"People think that if polar bears disappear from the ecosystem because of climate change, it will just mean there will be more seals. But this paper shows the linkages across the ecosystem," notes Derocher, adding that in regions where polar bear populations are declining, about 323,000 kg of carrion have been lost every year.
Because polar bears pull seals from the water and leave them on the ice, many scavengers have no other way of gaining access to the food. And as the ice melts due to climate change, it could become harder for some animals to reach the bears' leftovers. Carrion can act as a buffer for scavengers when food resources run low.
Derocher's team examined observational and anecdotal data of scavenging in the Arctic dating back to the 1930s, calculating how many seals polar bears consume each year, and how many calories seal blubber provides.
"We've had lots of birds, and Arctic foxes are the primary scavengers," says Derocher of his observations in the field. "They'll actually follow polar bears for long distances."
Derocher also says that if a polar bear kills a seal, it's common for other bears to smell it and come to see if there's a free meal.
"When we're near a seal kill out on the sea ice, we're on high alert. It's like the dinner bell has rung and everybody in the area is coming for a meal."
