Great white sharks，the world's largest predatory（食肉的）fish，eat three to four times more food than previously thought，an Australian study shows．

The U．S．research from the 1980s estimated a meal of 30kilograms could make a one-ton shark continue living for more than six weeks．

That made assumptions that large sharks could survive long periods without eating．

However，a University of Tasmania-led study published this week in Scientific Reports found that 30kg was only enough for 12-15days．

Researchers tagged （给…附上标签）a dozen great white sharks at Neptune Islands offSouth Australia and calculated their metabolic（新陈代谢的）rate based on swimming speeds．They worked out how much energy the sharks burned and how much food they required．

"Their metabolic rate is faster than we assumed．"

Jayson Semmens was the lead author on the study．He said，"They（U．S．researchers） picked a shark that probably wasn't working very hard at the time when they did it．At the time it was a new study．They did some metabolic work similar to us but on one shark．"

"The white sharks，which we tagged，are working pretty hard…they're coming up to some pretty high speed to catch the seals．"he said，"Their metabolic rate is much faster than what we had assumed．These animals are probably going to be feeding every day，rather than several weeks．"

The research also sought to improve understanding of how sharks fit into the ocean ecosystem．

"We don't have a good handle on the population sizes of white sharks．We know that sharks in general are under pressure around the world from overfishing，"Semmens said，"Furthermore，they're long-lived，they reproduce late in their life and they produce a small number of babies．"

Semmens said the effects of removing white sharks from the ocean were thus far more important than realized．"They're keeping under control a lot more anima