Featured Image Credit: © National Geographic Stock / Nick Caloyianis / WWF-Canada
By Laura O’Brien
In cold northern waters the world’s slowest shark, the Greenland shark, stalks its prey. But experts want to know, how does it catch its prey?! The sharks are known to eat fish and scavenge, which can explain some of their eating; but experts have found evidence inside of some Greenland shark’s bellies which suggest that these sharks may have some tricks up their sleeves.
Remains of seals have been found inside the bellies of some Greenland sharks, but it is not likely that the seals were scavenged because carnivorous invertebrates would usually appear with remains that had been dead for consumption. The suspicious absence of such invertebrates has left marine experts guessing how the slow Greenland sharks could be catching seals. Data collected from tracking some of the sharks indicates that their highest speed is still only HALF as fast as a seal. This is especially remarkable because these sharks are 10 foot long or even up to 21 feet moving at such a slow speed.
A marine biologist at Tokyo’s National Institute of Polar Research named Watanabe theorized that the sharks may sneak up on the seals as they sleep. This may be possible because Arctic seals are believed to sleep in the water instead of on sea ice as a precaution against the threat of polar bears. Watanabe even said that he once saw what he believed to be a dead seal floating in the water, but when he poked it the seal began to move. So he believes that it would not be far-fetched for a shark to sneak up on a sleeping seal.
Meanwhile, a different marine biologist believes that other another hypothesis may explain the sharks’ ability to hunt seals. Gregory Skomal, who works at the Massachusetts division of Marine Fisheries, proposed the idea that the sharks utilize camouflage and their slow movements to sneak up on conscious seals. He also acknowledged that the sharks might have actually scavenged the seals that were found in their bellies. Although there were no brittle stars or other carnivorous invertebrates in the shark’s bellies to suggest that the seals had been dead, he believes that those creatures could have adequate time to evacuate the corpse as the slow moving shark began eating it.
Clearly, there is still work to be done before scientists will discover how on earth the Greenland sharks could have seal remains in its belly. We look forward to the results of Watanabe’s new project, where his team will attach cameras to Greenland sharks in order to learn more about their habits.
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