Slowest Greenland sharks hunts sleeping prey

Data-logging tags revealed that Greenland sharks "cruise" at 0.34m per second - less than 1mph.

The study showed that, even when the languid fish embarks on a burst of speed in order to hunt, it is far too slow to catch a swimming seal.

Since the species is known to eat seals, the scientists think it probably "sneaks up on them" as they sleep under the water.

The Greenland shark was already known to be the world's slowest swimming shark, but its sluggishness surprised the scientists.

Yuuki Watanabe from the National Institute of Polar Research in Tokyo, who took part in the study, said that, when you account for the size of its body, it is the slowest fish in the ocean.

Previous research had revealed seal remains in the stomachs of the sharks.

"It was hard to understand," he told BBC Nature, "because [it would seem] impossible for them to catch fast-swimming seals."

The researcher joined Dr Kit Kovacs and Dr Christian Lydersen from the Norwegian Polar Institute , to tag Greenland sharks in the waters off Svarlbard.

The study, published in the Journal of Experimental Marine Biology and Ecology , was the latest part of an ongoing mission by the Norwegian researchers to find out what has been killing the harbour seals off Svarlbard's coast.

It was thought that Greenland sharks simply fed on the carcasses of dead seals on the seafloor, but the team recently discovered evidence that they were taking live seals.

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