In Shark Vs. Polar Bear Smackdown, Shark Wins

Aug. 15, 2008 -- Adult polar bears, among the largest and most powerful carnivores, are thought to have no natural enemies, but that assessment might change in light of a polar bear jawbone recently found in the stomach of a Greenland shark.

While Greenland sharks, which can grow up to 24 feet long, are known to have eaten large seals, porpoises, an entire reindeer and parts of a horse, the discovery is rare evidence that they may also feast upon polar bears.

"These sharks eat anything they find dead, and do some active hunting as well," Kit Kovacs, who made the find, told Discovery News.

"We cannot determine whether the young bear was carrion or not -- nobody can," added Kovacs, who is the leader of the Biodiversity Research Program at the Norwegian Polar Institute in Tromso.

Kovacs made the unusual discovery while investigating the deaths of multiple harbor seals at Svalbard, an Arctic archipelago. She suspected that Greenland sharks, one of two species of sleeper sharks there, might be the culprits. Prevalent in the region, they are one of few species that might be capable of taking down polar bears, which grow to around 10 feet and weigh up to 1,500 pounds.

Kovacs and her team performed autopsies on collected Greenland shark specimens. They were shocked to find the polar bear bone, but in hindsight, she said, "this finding is not likely to be anything new."

"Greenland sharks have been in the Arctic for millions of years," she explained, suggesting that fatal encounters between marine and terrestrial predators would be inevitable over such an extended period.