They only grow up to 6 cm (2.4 inches) yet are perhaps the most abundant creatures on the planet in terms of weight. Snow petrels nesting in Antarctica fly for up to eight hours to catch a meal of them.
Krill - small shrimp-like crustaceans which with modern technology can be used in fish feed, human dietary supplements, soya sauce flavouring, pharmaceuticals, or even to clean the paintings of Old Masters - are in increasing demand.
A "pink gold" which if fed to farmed salmon cut out the need for colorants to make the flesh pink, krill are extremely rich in Omega-3 fatty acids, linked to health benefits for people.
Occurring in all oceans but most abundant in the Southern Ocean, they are also the staple diet for seals, penguins and whales as well as for the snow petrels living on icy mountains inland, which fly more than 500 km (300 miles) for each meal.
But rising human demand for fish oils, likely to bring more competition from trawlers for krill, is causing concern that this keystone species near the bottom of the food chain should not be overfished.
"The krill catch is projected to go up with other countries getting involved," said Stephen Nicol, a krill expert at the Australian Antarctic Division, adding that current catches seem no threat to vast stocks.
"But there's a lot of concern because this is a keystone species - whales, penguins and seals depend on it," he told Reuters by telephone. "But part of that dependence is because there's a lot of krill." Led by Norway, annual krill catches total 120,000 tonnes, a tiny share of a Southern Ocean stock estimated at anywhere from 100 to 500 million tonnes. Japanese, South Korean and Polish vessels also have krill licences under an international deal.
Norway says it already thinks about the ecological impact of its krill fishing. "We are concerned to catch krill in an environmentally sustainable way," Norwegian Prime Minister Jens Stoltenberg told Reuters during a visit to the Troll research station, 250 km inland where snow petrels nest under rocks.
KRILL OIL: Norway's Aker BioMarine, which operates the most advanced krill trawler, aims to launch a krill oil diet supplement in 500 shops across the Nordic countries, and separately in the United States, by the end of March 2008.
"In 2007 we caught 40,000 to 45,000 tonnes of krill," said Helge Midttun, chief executive of Aker BioMarine. Assuming regulatory approval, the "Superba" oil capsule will be Aker's first krill product for humans.
Canada's Neptune Technologies & Bioresources will be its main competitor. On January 23, 2008, a US panel ruled that Neptune's oil, already sold as health oil in capsules, was also safe as an ingredient in food, paving the way for its wider commercialisation in the United States.
Neptune signed research deals in 2007 with Swiss food group Nestle and with the Yoplait dairy unit of US food maker General Mills Inc over use of krill in foods. "Krill is not over-fished ocean-wide ... we can still create a sustainable fishery," said Jerry Leape, director of the Antarctic Krill Conservation Project at the Pew Environment Group in the United States.
"But much of the fishery concentrates in areas where krill swarms are most convenient. And that is where many natural predators also depend on krill," he said, adding that trawlers should be forced to spread catches around the continent. Among predators, pigeon-sized snow petrels and Antarctic petrels are extreme examples of dependence on krill when nesting, since there is no food on land in Antarctica for them to eat.
"These birds fly 250 km before they find water, and further before they find krill," said Kim Holmen, research director at the Norwegian Polar Institute, at the base, which is surrounded by mountains that look like the homes of mythical trolls.
"When they leave their nest it's 6-8 hours before they collect any food," he said. When nesting, male and females share the trips, taking 3-5 days before arriving back with food. "It's a survival strategy. If you live closer to the shore you have more enemies and competition for nest sites," he said.
CATCH SAFEGUARDS: Krill fishing briefly peaked in the 1980s when the Soviet Union caught up to 500,000 tonnes a year and canned it for human consumption. But because krill release damaging enzymes and decay quickly, scientists say they probably tasted bad.
Net technology developed by Aker BioMarine delivers a stream of live krill onto the vessel, overcoming the enzyme problem and avoiding a damaging by-catch of other species.
Midttun of Aker BioMarine said the company was converting a second vessel for krill catches, alongside its existing Saga Sea. The company, which co-operates with the WWF conservation group in monitoring its krill fishing, says it might be able to catch 200,000 tonnes of krill a year in a few years' time.
Midttun said the Commission for the Conservation of Antarctic Marine Living Resources (CAMLR), which sets quotas, reckoned catches could sustainable rise to 1 percent of the total biomass of krill, or 5 million tonnes a year if the total was 500 million tonnes.
He said the Commission was a good way to manage the fishery - safeguards are being set up before big catches happen. Even so, CAMLR says it has been unable to stop illegal catches of the Patagonian toothfish, another Antarctic species it oversees.
But scientists say little is known about the history of fish stocks and global warming could be a problem - it is unclear how far krill depend on algae that bloom near the ice shelves around Antarctica, and climate change could melt some of the ice.