Giant Robotic Cages to Roam Seas as Future Fish Farms?
Brian Handwerk
for National Geographic News
August 18, 2009 
Someday such automated cages could herald an entirely new form of fish farming, with robotic cages roaming the seas, mimicking the movements of wild schools.
Photograph courtesy Ocean Farm Technologies
(See pictures of futuristic fish farms.)
Such motorized cages could help produce greener, healthier, and more numerous fish, just when we need them most.
The world's growing population is devouring seafood as quickly as it can be caught and has seriously depleted the world's wild fish stocks, experts warn. (See National Geographic magazine's "Saving the Sea's Bounty.")
The UN's Food and Agriculture Organization says 70 percent of all the worlds' fisheries are exploited—that is, barely able to replenish themselves at current catch rates—overexploited, or depleted. (Learn more about sustainable agriculture.)
Aquaculture, or fish farming, currently produces about half of the fish eaten worldwide and seems destined to play an even bigger future role. The UN organization estimates world seafood demand will spike 40 percent by 2030.
"We've got doctors and nutritionists asking us to eat more seafood because of the healthy benefits," said Michael Rubino, manager of the Aquaculture Program at the U.S. National Oceanic and Atmospheric Administration (NOAA).
"We're doing a better job of ending overfishing of our wild stocks," Rubino said. "But most people agree that even if we can do that, most of the increase in consumption is going to have to come from aquaculture."
Free-Floating Farms on Horizon?
Traditional fish farms typically consist of cages submerged in shallow, calm waters near shore, where they are protected from the weather and easily accessible for feeding and maintenance.
But raising fish in such close quarters can contribute to the spread of disease among the animals, and wastes may foul the waters. Cages must be moved to keep the waters clean and the fish healthy.
Deepwater cages offer cleaner, more freely circulating ocean water and natural food, which can yield tastier fish. But the deep-sea cages must be built to withstand the rigors of the deep ocean. And because they are harder for humans to access, "smarter," self-sufficient cages could be key.
That's one reason that Cliff Goudey, director of the Massachusetts Institute of Technology's Offshore Aquaculture Engineering Center, is building cages that can move under their own power.
Goudey has equipped an Aquapod cage, produced by Maine-based Ocean Farm Technologies, with a pair of 2.4-meter [8-foot] diameter propellers, which can be steered easily by controllers on a boat to which the cage is tethered.
Aquapods are composed of triangular panels covered with vinyl-coated, galvanized steel netting and come in sizes from 8 to 28 meters in diameter (26 to 92 feet in diameter).
Goudey's technology gives fish farmers a way to rotate cage locations without towing cages behind boats.
Fish Farming 2.0
Someday such automated cages could herald an entirely new form of fish farming.
They might be turned loose to mimic natural systems by following carefully chosen ocean currents. The robotic fish farms could help lead to larger, healthier crops of farmed fish far from crowded coastal areas, where farmed fish both suffer from poor water quality and, by producing waste, add to water woes.
Cages might even generate their own electricity by harnessing solar energy, wave energy, or other forms of renewable power.
"Why don't we just go with the flow and behave more like the way a large school of fish behaves?" Goudey asked. "I think most people would agree that would have a far less negative impact on the environment."
"I think the idea of mobile operations will be a natural evolution."
Goudey currently uses a small boat to carry a generator that powers the cage's propulsion, but the power source could easily be made smaller and placed in a buoy for more automated operation.
"The idea of a cage towing a buoy, with the buoy in radio contact with the shore, is quite feasible," he said. "It's a little futuristic for today's industry, but we could have a sensor on the cage which gives its heading and a GPS system to report its effective speed over the ground.
"From those two pieces of information, we could control it without actually being there."
Closer to Market
Brian O'Hanlon, founder of Snapperfarm, Inc., and Open Blue Sea Farms, saw Goudey's cage in use last year at his offshore aquaculture operation in Culebra, Puerto Rico.
"My long-term vision is to be farming off the coast of major markets," he said. "The idea is to bring the farms closer to market, and offshore technology with automated systems is one of the ways we can do that."
O'Hanlon explains that—given crowded coastal waters, environmental concerns, and high operating costs—it's not practical to create large-scale farms near many major markets—but the answer could lie with locations just over the horizon.
Not incidentally, the concept could produce a far better quality of fish for consumption.
"The further we go with cage technology, the deeper and further offshore we can go," he explained, "and that opens up areas with untapped resources.
"Every part of the ocean has variables, and every species has their ideal conditions. With mobile pens it's feasible to keep the fish in the most optimal conditions throughout their growth cycle," O'Hanlon said.
"I don't think anyone is putting out a mobile farm tomorrow, but I think we need to keep working on this."
Fishing With 'Dinner Bells'
Scott Lindell of the Massachusetts-based Woods Hole Marine Biological Laboratory is exploring a different technology, creating a cage that could actually coax fish to "catch themselves."
Last summer Lindell's team installed half of an Aquapod sphere, an "Aquadome," on the floor of Buzzards Bay, Massachusetts. Some 4,200 quarter-pound (hundred-gram) black sea bass were placed in the cage and trained over five weeks to gather whenever a "dinner bell" sound was played through a speaker.
Previously, aquarium-based tests had proven that the fish not only associated the sound with food, they also remembered that association for up to four weeks.
Later, with the seafloor dome left open, the fish became "free range" animals. They could hide and forage in nearby natural habitat, but they still returned to the cage after the dinner bell had rung.
"The first week we had a successful demonstration that fish were able to swim in and out of the cage and still responded to the acoustic feeding stimuli," Lindell explained.
Trouble soon arrived, however, in the form of schooling 8- to 10-pound (3.6- to 5.4-kilogram) bluefish. The voracious predators quickly discovered the dome and circled it day and night to feast on Lindell's subjects.
The bass took the hint and went into hiding.
"We quickly reached a point where no enticement with the sound or the release of food would induce them to risk their lives to come back to the cage," he said. "They would stay out of harm's way."
Despite the setback, however, Lindell believes the dinner-bell concept holds promise. He notes that other, less vulnerable species like flounder or cobia might fare better. If so, the technology could provide fish farmers with a valuable tool to help satisfy the world's growing seafood appetite.
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