The fishing industry is approaching a crisis. Once-rich fishing grounds such as the Grand Banks off Newfoundland are denuded; important species such as cod are becoming endangered; national fishing fleets argue ever more bitterly about fishing rights. And yet the obvious answer, fish farming, has problems of its own. For water is poor in food and oxygen, so fish do best in high dilution. Yet a commercial farm must pack its fish as densely as possible: depleting the water of oxygen, polluting it with waste and faecal matter, and maybe spreading disease. Daedalus now has a middle way.

Many fish farms ‘wall off’ a region of natural water with a net, and breed the fish behind it. Daedalus is taking this idea to extremes. His plan is to raise a shoal of fish to young adulthood in a farm, and then release them within a large net in the open ocean. He is designing a floating circular boom, suspended from which a huge closed net encloses a volume of sea like a vast tea-strainer. The mesh size is chosen so that the fish within the net cannot escape, and their predators (which must be bigger) cannot get at them; neither are they likely to be seriously invaded by unwanted species. At the same time, their food or prey (which must be smaller) can freely enter, and excreta can freely drift out. And, of course, clean bulk sea water will swirl through the net as if it were not there.

The final step is to set the whole thing adrift in the open sea. The fish will not even realize that they are trapped; they will behave like a free-living shoal. But radar reflectors and transponders on the circular boom will tell the owners where it is at any moment. When the fish have had time to grow big enough, a boat can go out to harvest them — either hauling in the net, or towing the whole thing back to port.

An unpowered ‘fish corral’ will drift freely with the current, and will not sustain a healthy flow of water through it — unless the fish themselves propel it, as they may. If not, its radar reflectors may have to be formed as sails, to drive it through the water. Remote control of those sails could even steer it about, though this erodes the simplicity of the scheme. Many details remain to be worked out; the optimum size of the fish corrals, the best locations for them, and ways of avoiding collisions with ships or hijacking by pirates. But when perfected, Daedalus's fish corrals should avert oceanic ecological disaster while providing a sustainable, predictable supply of healthy and nutritious fish.