Shrimp-like krill can thrive in icy waters 3,000 meters (9,800 ft) deep off Antarctica as well as near the surface, according to a study on Monday that shows krill stocks can survive far deeper than previously thought.The British researchers said, however, that the discovery of krill in the depths does not mean that stocks of the crustaceans sometimes called "pink gold" are far bigger than previously expected nor that trawlers can expect bigger quotas."Scientists have found Antarctic krill living and feeding down to depths of 3,000 meters in waters around the Antarctic peninsula," the British Antarctic Survey said of a study by a robot submarine to the sea floor."The discovery completely changes scientists' understanding of the major food source for fish, squid, penguins, seals and whales," it said in a report with the National Oceanography Centre in Southampton.Krill, which spawn near the surface, were previously thought to live only in waters down to about 150 meters. Traveling down to 3,000 meters deep means exposure to crushing pressure shifts."There aren't many organisms that will travel over that depth range. Krill is a lot more flexible physiologically and a lot more flexible behaviorally than we ever imagined," said Andrew Clarke of the British Antarctic Survey."Maybe that's why it's so successful," he told Reuters.Clarke, who co-authored the paper in the journal Current Biology, speculated that krill travel mainly to the sea floor to feed on algae falling from surface waters at the end of the Antarctic summer.If so, that would mean there was probably not a vast hidden stock of krill permanently in the depths. Krill, which grow up to about 6 cms (2.4 inches), would probably take about four hours to swim up to the surface again."Whether this has any practical significance in terms of fisheries, the honest answer is that we don't know but our suspicion is that it is no big deal," he said.Krill is used for everything from heart medicines to fish feed. Catches total about 120,000 tonnes a year -- led by Norway's Aker BioMarine.And krill in the depths would be too costly to catch."The effort involved for the return would not balance out," he said. "It's like looking for oil (in the Arctic) -- you don't look there first. But as the price goes up you do things in tougher environments."The British Antarctic Survey said that the total weight of Antarctic krill is calculated between 50-150 million tonnes but stocks seem to have dropped sharply since the 1970s, apparently because of a decline in winter sea ice.Krill grow under the ice, partly because algae also grow there and because it offers protection from predators. Other estimates put the total krill stock at up to 500 million tonnes.