New York, Oct 4 (IANS): Are whales indiscriminate grazers that consume copious amounts of tiny krill throughout the day? No, says a new study which finds that whales forage efficiently to optimise their energy levels.

The tagged blue whales in the study by researchers from NOAA Fisheries, Oregon State University and Stanford University revealed sophisticated foraging behaviour that targets the densest, highest-quality pretty, maximising their energy gain.

"Blue whales do not live in a world of excess and the decisions these animals make are critical to their survival," said principal investigator Ari Friedlaender from Oregon State University.

Adult blue whales can grow to the length of a basketball court and weigh as much as 25 large elephants combined, but they operate on an "energetic knife-edge", the researchers said.

They feed through the extreme mechanism of engulfing as much prey-laden water as they weigh and then filtering out the tiny krill (crustaceans found throughout the world's oceans) it contains.

But feeding expends tremendous amounts of energy and the dense krill patches they need to replenish that energy are often deep and difficult to find.

The study was published in the journal Science Advances.