The polar seas abound in krill, the tiny crustacea that live on plankton. The main predator of krill is the whale; now that the whaling industry has driven whales almost to extinction, the krill is richly abundant. So Daedalus plans to harvest it directly.

What is needed, he says, is some sort of automatic, self-propelled submerged vehicle that would wander at random around the polar seas, sucking in the krill like a giant vacuum-cleaner. When fully laden, it would return with its catch to a home port or a mother-ship. Modern robotics and satellite navigation techniques make this fairly simple in principle. But the devil, as ever, is in the details.

Daedalus's ‘oceanic filter-feeder’ is essentially an open framework whose bow is a huge filter. Its mesh is chosen to admit krill, but to exclude bigger fish, weed, flotsam and so on, which would complicate the processing downstream. As the craft travels round the ocean, it will strain the krill continuously from its densest stratum just under the surface. The main problem, of course, is that each voyage will continue for many days or weeks; the captured krill will die and rot long before it reaches port. Hence the need for processing: some form of on-board chemical engineering to preserve the catch. Daedalus's design cunningly splits the krill intake into two streams. The smaller stream will indeed be allowed to die and rot. It will ferment to methane gas, the fuel for the propulsion and electronics of the craft, and to carbon dioxide, which will be catalytically reacted with methane to give acetic acid (vinegar). The vinegar will pickle the larger stream of krill, preserving it in a huge flexible plastic ‘stomach’. When sensors on the stomach detect that it is full, they will switch the navigation system from ‘cruise’ to ‘homing’, and the filter-feeder will return to base with its catch.

Bulk pickled krill will be an intriguing new resource. Since filter-feeders could take over the whole ecological niche now being vacated by whales, there will be a lot of it. But despite the popularity of lobsters, prawns and other large crustacea, Daedalus doubts that krill as such will be welcomed by the chef and housewife. It may have to be ground up to a nutritious ‘fish-flour’, partially hydrolysed to a proteinaceous pabulum, or even fed to chickens. But one way or another, the ever-ingenious factory-food industry will put it to good use.