The world's ever-growing population is eating more and more fish and the oceans can't keep up. Fishing has depleted wild stocks of tuna, swordfish, cod and many other species.
Some scientists say the answer is a massive growth of fish farming -- a so-called "blue revolution" to help feed the planet. So far, fish farming has occurred on land or in protected harbors. But some see a future with large-scale off-shore fish farms in waters hundreds or thousands of feet deep.
One of the first companies venturing off-shore is Hawaii-based Kona Blue. It is raising fish in giant, netted cages off the coast of Hawaii, submerged in waters some 200 feet deep. Some scientists say that farming in such deep waters can avoid environmental concerns raised by fish farms close to shore. If you get too many caged fish in a harbor, the fecal matter will pollute it. But offshore at the Kona Blue site, powerful ocean currents constantly flush so much water through the farm that Kona Blue reports it can't detect any change in nutrient levels up-current versus down-current of the farm.
A big challenge, of course, for off-shore aquaculture is designing a fish farm that can survive the open ocean. Anyone who read the book or saw the movie The Perfect Storm got a sense of the forces that are unleashed on the ocean's surface.
The trick has been to sink the giant cages down well below the surface of the water and tie them to a series of anchors using high-strength polymer ropes. The only things exposed above water are several large metal feed buoys. One experimental fish farm off the coast of New England has survived several northeasters with 40-foot waves and high winds.