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April 16, 2014  |  Login
Open Ocean Aquaculture
By John Rubino
 

Fish farming's main drawback is that it's done in close quarters. Shore-based pens are fenced and stationary, and are generally located in a placid body of water like a bay without swift currents or big waves. Because the water doesn't move fast enough to carry away the waste and food particles that commercial quantities of fish generate, the area gets dirty, the fish get sick, and both neighbors and customers complain. Meanwhile, there's this big ocean right nearby, with thousands of miles of open water capable of absorbing anything a single school of salmon can throw at it. So why not put the farms out to sea?

For over a decade, a Seattle company called Net Systems has been selling huge SeaStation model enclosures that make it possible to site fish farms miles from shore, where currents guarantee a continuous flow of clean seawater. The enclosure is a rigid cage that's wide in the middle and tapered at the top and bottom, covered with "predator proof" netting made of Spectra, a superstrong polyethylene fiber used by NASA to tether spacewalking astronauts. Current models are in the range of 50 feet high by 80 feet wide, which is big enough to hold tens of thousands of fish. A steel cylinder runs from the bottom of the cage to the top and is capped by a pump that forces air in and out of the cylinder to raise or lower the enclosure. Depending on the mix of air and water, the cage floats on the surface or sinks to 40 feet to 60 feet, where even in surface storms the sea is placid. Another company, Maine-based Ocean Farm Technologies, is developing a line of spherical geodesic enclosures that operate basically the same way, though, it claims, with cost and scalability advantages.

The theoretical advantages of open ocean fish farming are many: The enclosures are virtually invisible from shore-all you see is a single buoy. Ocean currents keep the fish healthy without the need for antibiotics, and the size of the ocean minimizes the impact of fish waste. Attracted by the possibilities, universities and governments around the world are running feasibility tests. The U.S. government and the University of Hawaii are operating a prototype open ocean fish farm anchored in 100-foot waters 2 miles off Hawaii's Ewa Beach. The researchers fill the cage with 70,000 baby moi, a local delicacy, feed and monitor them, and harvest them when they're grown-at a cost that's estimated to be comparable to current market price. Other studies, most using Net Systems enclosures, are ongoing in at least 10 other countries.

Two private companies are already farming this way: Puerto Rico-based Snapperfarm raises cobia 2 miles off the local coast in Net Systems and Ocean Farm Technologies enclosures. According to Snapperfarm, strong currents refresh the enclosures' water over 1,000 times per day, which keeps the fish healthy, allowing it to market its cobia as "all natural, free of hormones, pigments, drugs, and antibiotics." Studies by the Universities of Miami and Puerto Rico have, again according to the company, found no significant environmental impact. Hawaii-based Kona Blue Water Farms, meanwhile, operates a hatchery and offshore farm system that raises Kona Kampachi, a "sushi-grade Hawaiian yellowtail" in pens half a mile off the Kona, Hawaii, coast. Here again, brisk currents keep the fish healthy without drugs.

The offshore farming concept appears to have potential for shellfish, too. The University of New Hampshire and some local fishermen have successfully convinced mussels to grow along lines suspended from buoys far from shore. The shellfish filter water for microorganisms and require no other food or drugs, and because the deep water is calmer, they develop thinner shells and more meat, making them more marketable than their close-to-shore cousins.

 
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